Research Catalog

Demonstrates that a molybdenum-based near-infrared spin-flip emitter serves as a triplet-selective energy acceptor from tetracene-based singlet fission (SF) dimers. The large energy gap between spin-allowed transitions and the luminescent spin-flip transition of the Mo complex enables efficient exothermic triplet energy transfer (TET) to the spin-flip excited doublet state while circumventing the competing Forster resonance energy transfer (FRET) from the initially formed tetracene singlet. Quantum yields of Mo complex doublet state formation by tetracene SF dimers with phenylene, 2,5-methylphenylene, and p-terphenylene bridging units were 112 +/- 6%, 132 +/- 2%, and 128 +/- 4%, respectively, in solution. The drop of fluorescence lifetimes at high Mo complex concentrations implies energy transfer from exchange-coupled triplet pairs.

Published in JACS today (March 25, 2026) from the Kimizuka/Sasaki group at Kyushu University (a world-leading TTA-UC lab) with Heinze group at JGU Mainz. 132% quantum yield demonstrates photon multiplication via SF + selective triplet harvesting. The spin-flip emitter concept is directly relevant to TTA-UC: (1) Sasaki/Kimizuka are major TTA-UC researchers, (2) tetracene dimers are key TTA-UC annihilator scaffolds, (3) the selective TET mechanism (avoiding FRET loss) informs sensitizer-to-annihilator energy transfer design, (4) Mo spin-flip emitters could serve as novel triplet acceptors/mediators in TTA-UC systems. The reverse engineering principle applies: understanding selective triplet harvesting from SF dimers improves selective triplet injection into TTA annihilators.

Comprehensive review examining porous framework materials - including metal-organic frameworks (MOFs) and porous aromatic frameworks (PAFs) - as platforms for TTA-UC. Provides detailed analysis of the intrinsic structure-performance relationships in these materials, highlighting how their diverse functional and structural characteristics enable efficient, oxygen-resistant, solid-state TTA-UC systems. Summarizes recent advances and applications in bioimaging, sensing, and photocatalysis. Discusses prevailing challenges and proposes prospective solutions for the field.

Published in Small (online March 20, 2026, ahead of print). From Ming-Yu Zhang and Ling Huang, now at Nankai University (Research Center for Analytical Sciences). Zhang is a prolific contributor to TTA-UC framework research (co-author of the COF TTA-UC paper in Chem and the BODIPY ligand Chem Sci paper in the catalog). This review consolidates the rapidly growing subfield of framework-based TTA-UC, complementing the Isokuortti/Nienhaus solid-state annihilator perspective and the Li et al. oxygen-tolerance review already cataloged. MOFs and PAFs address both the oxygen quenching and solid-state translation challenges simultaneously.

Demonstrates plasmon-enhanced NIR-to-blue TTA upconversion using a monolayer WSe2 (2D transition-metal dichalcogenide) as the sensitizer in a WSe2/organic heterojunction. Under far-field excitation the device reaches a threshold of 19 mW/cm2 and an external quantum efficiency (EQE) of 0.17% with a 1.1 eV anti-Stokes shift. Surface plasmon polariton (SPP) excitation lowers the threshold to 0.9 mW/cm2 and boosts EQE to 3.6%. The plasmon enhancement is attributed to SPP near-field enhancement and dark-exciton absorption in WSe2. Optimization of the WSe2 transfer process is identified as a key performance factor.

From the Rand group (Princeton), authors of the Nature Photonics plasmon-enhanced TTA-UC paper already in the catalog. This companion study introduces 2D TMD monolayers as a fundamentally new class of sensitizer for solid-state TTA-UC. The 0.9 mW/cm2 threshold under plasmon excitation is among the lowest reported for solid-state upconversion. WSe2 dark excitons as a triplet source is a novel mechanism. Published in Nano Letters, March 2026.

Demonstrates solid-state NIR-to-visible TTA-UC at the 1 um edge using ruthenium sensitizers with spin-forbidden S0-to-T1 absorption. By exploiting the direct spin-forbidden excitation pathway, the Ru sensitizer series bypasses the large ISC energy loss inherent to conventional S1-mediated sensitization, enabling excitation at and beyond 1000 nm in solid-state films. Addresses the molecular tunability advantage of Ru complexes while tackling the threshold intensity challenge that spin-forbidden absorption faces compared to semiconductor sensitizers like PbS QDs.

Published in JPCL just 3 days ago. From the Segawa group (University of Tokyo), leaders in TTA-UC for photovoltaics. Pushing solid-state molecular TTA-UC to the 1 um edge is extremely significant for silicon photovoltaic applications - this is exactly the spectral region where sub-bandgap photon harvesting would boost efficiency beyond the Shockley-Queisser limit. Complements the computational Vitillo telecom band paper and the Ho pseudo-solid-state QD paper already in the catalog.

Comprehensive review examining recent progress in aqueous TTA-UC from a nanostructured materials design perspective. Rather than focusing solely on photophysics, discusses how different material architectures - nanocapsules, micelles, liposomes, microemulsions, hydrogels, nanoparticles, supramolecular assemblies, and metal-organic frameworks - have been engineered to enable efficient upconversion in water by controlling molecular confinement, interfacial environments, and oxygen accessibility. Critically compares structure-property relationships that determine triplet energy transfer, annihilation efficiency, and operational stability in aqueous media.

Published 3 days ago in Materials Today Chemistry. Aqueous TTA-UC is a critical frontier for biomedical applications. The materials-oriented framework comparing different nanostructured platforms (nanocapsules vs micelles vs liposomes vs hydrogels vs MOFs) provides practical design guidance that complements the oxygen-tolerance review from Li et al. already in the catalog. Open access.

Develops nanostructured polymer scintillators that exploit sensitized triplet-triplet annihilation for improved gamma-ray vs neutron discrimination via pulse shape discrimination (PSD). Extends the Monguzzi/Weder groups prior work (Adv. Mater. 2024) on TTA-based polymeric scintillators by engineering the nanostructured polymer matrix to enhance sensitized triplet exciton generation, enabling faster and more reliable PSD. The nanodomains within the polymer preserve liquid-like chromophore dynamics needed for efficient TTA while maintaining a solid macroscopic form factor. Demonstrates a completely new application domain for TTA photophysics beyond energy conversion and photocatalysis.

Published in Adv. Funct. Mater. (March 2026). From the Monguzzi group (Milano-Bicocca) and collaborators at the Adolphe Merkle Institute (Fribourg, Weder group). Nuclear radiation detection is a novel and high-impact application domain for TTA - the spin-dependent dynamics that govern TTA also encode information about the type of ionizing radiation. Builds on the groups 2024 Adv. Mater. proof of concept. The nanostructured polymer matrix design is directly relevant to solid-state TTA-UC more broadly.

Reveals that hydrocarbon ligands on nanoparticles can remotely govern secondary triplet energy transfer (TET2) from triplet mediators to annihilators, which occurs entirely outside the QD core. By shrinking the native oleate ligand shell on PbSe QD sensitizers before attaching triplet mediator ligands, NIR-to-visible upconversion performance improves dramatically. Transient absorption spectroscopy confirms the compact ligand shell boosts TET2 efficiency from 59.4% to 93.5%. Molecular dynamics simulations attribute the enhancement to shortened mediator-annihilator distances from reduced steric hindrance. The strategy is versatile across multiple systems: PbSe NIR-to-visible, CdSe green-to-blue, solid-state films, and even lanthanide-doped nanoparticle hybrids. The same principle applies to singlet fission downconversion, boosting photon-multiplication efficiency from 132% to 163%.

Published in ACS Nano, March 13, 2026. Features Victor Gray and Akshay Rao (Cambridge) as co-authors, both leading figures in QD-based triplet photophysics. The finding that native hydrocarbon ligands remotely control energy transfer occurring outside the QD core is a new mechanistic insight with broad implications. The 59.4% to 93.5% TET2 efficiency boost is dramatic. Versatility across PbSe, CdSe, solid-state, and lanthanide systems demonstrates generality. Directly complements the Nishimura/Gray JPCC paper on aliphatic ligand roles and the Luo et al. JPCL alloyed QD paper (same research group) already in the catalog.

Demonstrates triplet-triplet annihilation photopolymerization (TTAP) for vat-based 3D printing using PtOEP as sensitizer and DPA as annihilator. DPA serves a dual role as both annihilator and auxiliary oxygen scavenger, reducing inhibition time. The super-linear intensity dependence of TTA provides enhanced photochemical curing contrast compared to conventional single-photon polymerization, enabling higher resolution 3D printing at lower light intensities.

First demonstration of TTA-enhanced curing contrast specifically for DLP 3D printing. The dual-role DPA strategy (annihilator + O2 scavenger) addresses the oxygen quenching problem elegantly. Published in Adv. Funct. Mater. just 2 days ago. Extends TTA-UC applications beyond energy/sensing into additive manufacturing.

Demonstrates a new proton shuttle-assisted mechanism for spin-triplet migration from photoexcited colloidal quantum dots to surface-anchored molecular moieties. Establishes a previously unknown pathway for triplet energy transfer mediated by proton-coupled processes, directly relevant to nanocrystal-sensitized TTA-UC systems where QD-to-molecule triplet transfer is the efficiency-limiting step.

First demonstration of proton-coupled triplet energy transfer. Published in Nature Materials. Could open new design strategies for QD-sensitized TTA-UC by leveraging proton shuttling at the nanocrystal-molecule interface.

Reports a novel mono-styryl-BODIPY surface ligand on PbS quantum dots that achieves 65.4% triplet exciton transfer efficiency with only seven ligands per QD (low coverage). Using rubrene as annihilator, achieves 16.8% upconversion quantum yield (normalized to 100%). The BODIPY ligand is more stable than tetracene-based alternatives. Coupling with BPEA annihilator achieves 808 nm to 480 nm upconversion (record anti-Stokes shift for NIR QD-based TTA-UC into the cyan-blue region), with 6.5% efficiency.

Published as Chem. Sci. Edge Article (open access, March 5, 2026). From the Ling Huang group (same lab as the 830 nm selenium-cyanine JACS paper). BODIPY ligands are a new class for QD-based TTA-UC, offering stability advantages over tetracene. Record anti-Stokes shift into cyan-blue from 808 nm NIR excitation. Low ligand coverage (7 per QD vs 25 for InAs) addresses processability challenges.

Demonstrates visible imaging of incoherent 1200-nm NIR light using thin-film TTA-UC. A single-layer bulk heterojunction integrates PbS quantum dots as tunable NIR absorbers with a TES-ADT organic semiconductor matrix. Achieves anti-Stokes shifts up to 500 nm and high internal quantum efficiencies across the NIR-I and NIR-II windows (800-1200 nm). 5-tetracene carboxylic acid ligands on PbS QD surfaces boost sensitized triplet yield, yielding a 15-fold improvement in UC efficiency. Images formed at intensities as low as 20 mW/cm^2.

From the Congreve lab (Stanford) and collaborators at Wisconsin-Madison, UNSW, and SLAC. Pushes TTA-UC into practical NIR imaging territory with 1200 nm excitation. The bulk heterojunction architecture and ligand engineering (5-tetracene carboxylic acid) for enhanced triplet yield are broadly applicable design strategies. Preprint updated March 2026.

Introduces di(p-anisyl)tetrahydropentalene (TP-Ans) as a new symmetric, rigid annihilator for TTA-UC. The tetrahydropentalene core provides structural rigidity that suppresses nonradiative decay, while the p-anisyl substituents tune the electronic properties. Demonstrates efficient TTA-assisted photon upconversion with this previously unexplored chromophore class. Expands the annihilator design space beyond the established anthracene, perylene, and rubrene families.

New chromophore class for TTA-UC annihilators. Tetrahydropentalene derivatives are structurally distinct from established annihilators (DPA, perylene, rubrene, TIPS-naphthalene). The same group has prior publications on tetrahydropentalene luminescence properties (Asian J. Org. Chem. 2025). ChemRxiv preprint from Osaka Metropolitan University.

Constructs a high-performance NIR-II TTA-UC system operating beyond 1000 nm using quantum dot sensitizers, and demonstrates its application in driving sunlight-powered photocatalysis with low-energy photons that would otherwise be wasted. Extends the practical spectral range of QD-sensitized TTA-UC deep into the NIR-II window, enabling photocatalytic reactions powered by photons below silicon's bandgap energy. Represents the first demonstration of TTA-UC-driven photocatalysis using >1000 nm sunlight.

Published in National Science Review (IF ~17), one of the highest-impact general science journals. From the Ling Huang group (Central China Normal University), who have multiple papers in the catalog (Se-cyanine JACS, BODIPY ligand Chem. Sci., nanoconfinement Small Methods, color-tunable JPCC). Pushing TTA-UC photocatalysis beyond 1000 nm is a critical milestone for real-world solar energy utilization - this is the spectral region where the largest untapped photon flux exists.

Synthesizes polynorbornenes with both platinum-acetylide complex (triplet sensitizer) and 9,10-diphenylanthracene (DPA, annihilator) moieties covalently attached to the polymer side chains. Creates self-contained macromolecular TTA-UC systems where both components are fixed in the polymer backbone at controlled ratios. Evaluates photoluminescent properties and triplet energy transfer within the polymer. Continues the AIST/RPTU group's systematic work on polynorbornene-based TTA-UC platforms (Polym. Chem. 2021, 2024).

Polymer-based self-contained TTA-UC systems address the practical challenge of chromophore aggregation and phase separation in solid-state devices. Covalently attaching both sensitizer and annihilator to polymer side chains enables controlled intermolecular distances. From AIST Japan. Published in Polym. Chem. vol 17, issue 9, pp 954-962.

Proposes a simple and rapid method for determining the threshold excitation intensity of TTA-UC systems from a single snapshot of the emission image. The threshold intensity is a key parameter characterizing TTA-UC performance - it marks the transition from quadratic to linear intensity dependence and dictates practical applicability under solar illumination. The snapshot method reduces measurement time from minutes (conventional intensity-by-intensity scanning) to under one second, with accuracy comparable to the conventional approach.

Published in Optics Express vol 34, issue 5. Methodology advance rather than new materials, but the practical impact is significant - fast threshold measurements enable high-throughput screening of TTA-UC systems. Synergistic with the Baronas automated platform paper (ACS Central Science) already in the catalog. From AIST Japan.

Review examining how molecular chirality impacts both singlet fission (SF) and triplet fusion (TF, i.e., TTA). Covers dendrimers with pentacene coronas (for SF) and anthracene coronas (for TTA-UC). Reports 50-fold enhanced dissymmetry factor for UV circularly polarized luminescence (UVCPL) realized via triplet energy transfer followed by TTA-UC. Discusses how chiral packing and spin-orbit coupling modulation affect triplet pair dynamics.

Directly covers triplet fusion (= TTA) as one of its two main topics. Chirality as a design handle for modulating TTA yield is underexplored. The 50x enhanced CPL dissymmetry via TTA-UC is a striking result. Dendrimers with anthracene TTA coronas are novel annihilator architectures. Published in ACS Energy Letters.

Perspective article examining molecular design principles for solid-state TTA-UC annihilators. Proposes a unified excitonic framework linking upconversion with OLEDs and singlet fission. Discusses controlling triplet exciton diffusion, maximizing singlet formation, and suppressing loss channels (excimer/trap states). Advocates for data-driven machine learning + phonon engineering to surpass the solution-first approach.

Key perspective from Rice University (Nienhaus group). Bridges TTA-UC with OLED and singlet fission communities. Proposes ML-driven design as next frontier for solid-state upconversion.

Uses QD-sensitized TTA-UC as a testing platform to show that Te doping in alloyed quantum dots enhances exciton wave function delocalization, which boosts triplet energy transfer and upconversion efficiency. Demonstrates that tuning QD composition (alloying) is a viable strategy for improving nanocrystal-sensitized upconversion.

Direct TTA-UC application study. Demonstrates composition-tunable QD sensitizers for improved TTA-UC. Practical route to better nanocrystal sensitizers.

Addresses a key loss mechanism in solid-state TTA-UC: singlet energy back transfer from the annihilator back to the sensitizer. Demonstrates strategies to suppress this parasitic channel, improving overall upconversion efficiency in solid-state materials.

Tackles a well-known but underexplored loss channel. Practical implications for solid-state TTA-UC device optimization.

Demonstrates ultrafast singlet fission at interchromophore distances up to 16 A (previous limit was ~5.6 A) by using nitrogen-doped carbon nanohoops to co-optimize through-bond and through-space charge-transfer interactions. SF occurs in under 4 picoseconds. Shows that strong electronic coupling can be achieved without dense molecular packing, overturning assumptions about van der Waals proximity requirements for SF.

Published in Nature Chemistry. Singlet fission is the reverse of TTA - materials that undergo efficient SF are prime candidates as TTA annihilators. The ability to achieve SF at 16 A via through-bond coupling in nanohoops could inspire new organized TTA-UC annihilator arrays with controlled spacing. Paradigm shift for chromophore assembly design.

Develops TTA-UC based photoluminescence temperature sensing. Exploits the temperature dependence of triplet diffusion and annihilation dynamics to create optical thermometers. Demonstrates the utility of TTA-UC beyond energy conversion in sensing applications.

Sensing is an important application niche for TTA-UC. Temperature sensing via TTA-UC dynamics is a creative use of the intrinsic temperature sensitivity of triplet processes.

Develops organic-inorganic hybrid layered porous materials for TTA-UC by integrating anthracene-based emitters into zeolite frameworks using click chemistry. Demonstrates a new approach to confining TTA-UC chromophores in ordered porous hosts, potentially improving oxygen tolerance and structural control.

Novel host material approach for TTA-UC. Click chemistry enables precise molecular placement in zeolite interlayers. Addresses the challenge of bringing solution-phase TTA-UC into solid-state ordered frameworks.

Demonstrates the first TTA-UC system capable of upconverting NIR excitation beyond 800 nm to the deep-blue spectral region. Uses PbS quantum dots as sensitizers, perylene-3-carboxylic acid (3-PYCA) as a novel mediator, and perylene as an annihilator with triplet energy levels precisely engineered within 0.06 eV. Achieves an exceptional anti-Stokes shift of 1.3 eV (record for QD-based TTA-UC), with a high quantum yield of 2.1% (out of 50% max), an order of magnitude improvement over previously reported QD-based systems with anti-Stokes shifts above 0.8 eV. The upconverted deep-blue light efficiently drives cis-to-trans photoisomerization of azobenzene, demonstrating NIR-triggered photochemical applications.

Record anti-Stokes shift of 1.3 eV for QD-based TTA-UC. Order-of-magnitude QY improvement for large-shift systems. The three-component approach (QD sensitizer + molecular mediator + annihilator) with sub-0.1 eV energy tuning is a masterclass in triplet energy alignment. Open access in Chem. Sci. From Tianjin University and Chalmers.

Systematic study of how chemical substitutions at the 4-positions of diphenylanthracene (DPA) affect TTA-UC efficiency. Synthesized DPA derivatives with electron-donating and electron-accepting substituents at both 4-positions. DCl-DPA showed the highest fluorescence quantum yield, followed by DCN-DPA. However, unsubstituted DPA still achieved the highest UC quantum efficiency, followed by DCl-DPA and DCN-DPA. Analysis of saturated UC quantum efficiency, triplet-triplet energy transfer quantum yield, and TTA quantum yield revealed that the TTA quantum yield (phi_TTA) primarily governs the overall UC performance, providing design rules for annihilator optimization.

From the AIST Japan group (same group as the Horino polynorbornene paper in the catalog). Systematic substituent study on the most widely used TTA-UC annihilator (DPA). The finding that phi_TTA is the dominant factor governing UC efficiency is a useful design insight, though the conclusion that unsubstituted DPA remains optimal is a somewhat sobering result for the annihilator engineering community. Published in J. Phys. Org. Chem.

Low-toxicity (Cd-free, Pb-free) blue ZnSe-based quantum dots efficiently sensitize the triplet states of surface-anchored thioxanthone (ketone) molecules. This hybrid QD-ketone sensitizer enables three challenging photochemical applications: (i) visible-to-ultraviolet B photon upconversion via TTA with a large anti-Stokes shift of 0.8 eV, (ii) energy transfer photocatalysis (disulfide-ene reaction), and (iii) reductive aryl dechlorination and C-N coupling driven by thioxanthone triplet hydrogen abstraction.

From the Kaifeng Wu group (same team behind the Nature Materials proton shuttle paper). Opens a new class of low-toxicity QD sensitizers for TTA-UC - ZnSe QDs are non-toxic unlike PbS/CdSe. Vis-to-UVB upconversion is an underexplored spectral direction. The ketone triplet sensitization mechanism is novel and could expand the sensitizer toolkit for TTA-UC. Published in Small.

Computational study pushing the frontier of TTA-UC into the silica telecom band (beyond 1250 nm). Identifies molecular candidates that could enable upconversion of deeply NIR photons relevant to both solar energy harvesting and optical communications.

Extends TTA-UC into previously unexplored spectral territory. Computational predictions for telecom-band upconversion could bridge photovoltaics and telecommunications applications.

Demonstrates TTA-UC in covalent organic frameworks (COFs) with tunability of both interface and bulk exciton dynamics. COFs provide highly ordered, porous scaffolds that can organize sensitizer-annihilator pairs at the molecular level, offering a materials platform with applications across photovoltaics, photocatalysis, bioimaging, and anti-counterfeiting.

Published in Cell Press's Chem. COFs are a hot materials class, and achieving tunable TTA-UC within them is significant. The interface vs bulk exciton tunability is a new design handle for solid-state TTA-UC.

Feature article reviewing computational approaches for modeling triplet energy transfer (TEnT) processes. Covers diabatic state methods, the two-state and four-state models for TEnT, and the challenge of properly including charge-transfer states. Discusses applications to biological systems, photocatalysis, and materials design. Highlights future directions including reliable and computationally efficient prediction of TEnT kinetics.

Triplet energy transfer from sensitizer to annihilator is the first key step in TTA-UC. Better computational tools for predicting TEnT rates and mechanisms directly enable rational design of TTA-UC sensitizer-annihilator pairs. Feature article in Chem. Commun. from University of Louisville.

Uses sensitized TTA-UC nanoparticles to convert red light into blue light, which then drives aqueous radical polymerization. Demonstrates that TTA-UC can be coupled to photoredox catalysis using low-energy NIR/red excitation, enabling polymerization reactions under biologically benign light conditions.

Important application demonstration. Aqueous radical polymerization driven by red-to-blue TTA-UC bridges the gap between upconversion photophysics and synthetic polymer chemistry.

Demonstrates TTA-UC sensitized by an earth-abundant iron complex, overcoming the diffusion limit through preassociation of the sensitizer-annihilator pair. Couples the upconverted photons to drive photocatalytic reactions. Addresses the sustainability challenge of replacing precious metal sensitizers (Pd, Pt, Ru, Ir) with iron.

Iron-based sensitizers for TTA-UC are extremely rare and highly sought after. Overcoming the diffusion limit via preassociation is a clever strategy. Already cited by 1 paper within a month. Major sustainability advance for TTA-UC photocatalysis.

Reports aminal-linked covalent organic frameworks as robust solid-state platforms for TTA-UC. Addresses the challenge of translating solution-phase TTA-UC into practical solid-state materials using COFs with aminal linkages that provide structural stability and appropriate chromophore spacing.

Published in Angewandte. Aminal linkages are a new COF chemistry for TTA-UC (complementary to the Zhang et al. Chem paper on COFs). Solution-to-solid translation is a key challenge in the field.

Generates a powerful p-terphenyl radical anion super-reductant through sensitized blue-to-UV TTA upconversion. The super-reductant is long-lived and drives challenging reductive photocatalytic transformations. Full mechanistic resolution of the TTA-UC-to-photocatalysis coupling provided.

From the Wenger group (Basel), leaders in TTA-UC photocatalysis. Generating super-reductants via TTA-UC extends the accessible redox window for photocatalysis far beyond what direct visible-light excitation can achieve. Already cited.

A needle-shaped gold nanocluster Au42(PET)32 serves as a powerful triplet sensitizer, enabling rubrene to fully express its intrinsic annihilator capability (spin statistical factor f = 0.58). Achieves record-high upconversion internal quantum yields of 21.4% (808 nm excitation) and 15.0% (936 nm excitation), showcasing gold nanoclusters as a new class of TTA-UC sensitizers.

Record quantum yields for NIR-to-visible TTA-UC. Gold nanoclusters as sensitizers is a nascent paradigm. The 936 nm excitation at 15% QY is remarkable for approaching the tissue transparency window. Published in Angewandte.

Investigates how aliphatic surface ligands on PbS quantum dots influence triplet energy transfer efficiency in QD-sensitized TTA-UC using TES-ADT as the annihilator. Reveals that the native oleic acid ligand shell structure plays critical roles in mediating triplet energy transfer from QD to annihilator. Provides design guidelines for optimizing ligand shells in QD-based TTA-UC systems.

From Victor Gray's group. Cited by 1 already. Addresses the understudied role of native aliphatic ligands (not chromophoric transmitter ligands) in QD-based TTA-UC. TES-ADT is the same annihilator used in the Congreve and Lekavicius aggregation studies, making this synergistic with those works. JPCC vol 130, issue 7, pp 2616-2624.

Demonstrates visible-to-UV upconversion using TADF luminophores 4CzBN and 4CzIPN as heavy-atom-free triplet sensitizers paired with bis(phenylethynyl)benzene (BPEB) and an alkoxylated BPEB derivative as annihilator/emitters. The small singlet-triplet gap of the TADF sensitizers enables efficient ISC without precious metals, and the BPEB annihilators provide UV emission. Extends the Monguzzi/Weder groups' prior work on BPEB-based vis-to-UV TTA-UC systems (J. Mater. Chem. C, 2025) to purely organic, heavy-atom-free sensitization.

From two leading groups in TTA-UC (Monguzzi at Milano-Bicocca and Weder at Fribourg). TADF sensitizers for vis-to-UV TTA-UC expand the heavy-atom-free sensitizer toolkit. BPEB annihilators are a newer class of UV emitters for TTA-UC. Published in ChemPhotoChem vol 10, issue 1 (2026).

Introduces a 2D perovskite spacer layer between a bulk 3D perovskite sensitizer and a rubrene emitter to mitigate singlet exciton back-transfer via FRET. Reveals the balance between efficient triplet transfer across the interface and suppression of near-field singlet back-transfer. The spacer layer enhances relative upconversion efficiency at lower excitation power densities and sustains performance over longer timescales.

Directly addresses the singlet back-transfer loss channel in perovskite-sensitized TTA-UC (complementary to the Gou et al. solution-phase study). The 2D perovskite spacer is an elegant engineering solution. Enhancing low-power performance is critical for solar applications. Published in Adv. Opt. Mater. (vol. 14, no. 6, 2026). Also on arXiv: 2505.05801.

Discovers that controlled aggregation of the TES-ADT annihilator can boost the spin-statistical factor (f) from ~20% to ~60%, a 3-fold enhancement. DFT calculations show dimerization-induced energy level shifts make higher triplet states (up to T6) accessible, facilitating spin-conversion processes that favor singlet formation after TTA. This overturns the conventional view that aggregation is always detrimental and provides a new design handle for improving UC efficiency through molecular packing.

The spin-statistical factor f is a fundamental bottleneck in TTA-UC. A 3-fold enhancement via controlled aggregation is a paradigm shift - previously, aggregation was assumed to be harmful. From Vilnius University. Open access (Chem. Sci. Edge Article). TES-ADT is the same annihilator used in the Congreve group's NIR imaging work, making this directly synergistic.

Develops a strategy to activate solid-state TTA-UC in materials previously known only for singlet fission, specifically diketopyrrolopyrroles (DPPs) and dipyrrolonaphthyridinediones (DPNDs). Demonstrates a general approach to progressively enhancing UC quantum yields by appending bulky alkyl moieties to annihilator chromophores, suppressing aggregation-induced quenching. Achieves solid-state TTA-UC quantum yields up to 1.5% in thin films. Establishes that careful molecular design of annihilators is a powerful strategy for efficient solid-state upconversion.

Published in JACS. Bridges singlet fission and TTA-UC communities by showing SF-active chromophores (DPPs, DPNDs) can be repurposed as TTA-UC annihilators with bulky substituents. The general design principle (steric bulk to suppress quenching) is broadly applicable. From the Pun group.

Demonstrates that a selenium-integrated heptamethine cyanine dye acts as an effective NIR photosensitizer for TTA-UC, achieving 830 nm excitation with 557 nm emission and an upconversion quantum yield of up to 1.0% (out of 50%) when paired with rubrene as the annihilator. The selenium atom promotes intersystem crossing via the heavy-atom effect while maintaining good absorption in the NIR. Also demonstrates a single-layer 830 nm-responsive TTA-UC film with excellent transmittance, promoting practical photon upconversion applications in solar energy harvesting.

Published in JACS (same issue as Huang group's Accounts review - suggests this is from the same lab). 830 nm excitation using an all-organic (no precious metals) selenium-cyanine sensitizer is significant for practical NIR TTA-UC. The film demonstration adds device relevance. Complements the Mitsui Au42 nanocluster approach for NIR excitation.

Demonstrates color-tunable TTA-UC emission under a single excitation wavelength by exploiting the solvatochromism of specially designed annihilators. Solvent polarity shifts the upconverted emission color without changing the excitation source or the sensitizer. Establishes a new design paradigm for intelligent photon upconversion systems where the emission color responds to the local chemical environment.

From the Ling Huang group (Central China Normal University), one of the most prolific TTA-UC labs in 2026. Color tunability via solvent polarity is a neat concept for sensing and smart materials. JPCC vol 130, issue 2, pp 1088-1095.

Develops a series of novel symmetrical biphenyls bearing silylethynyl substituents of varying sizes as annihilators for visible-to-UV upconversion. TIPS-ethynyl and trimethylsilylethynyl groups yield UC quantum yields up to ~12%, while larger triphenylsilylethynyl substituents halve performance due to nonradiative loss channels from altered higher triplet state energies. The best annihilator (bTIPS-BP) extends efficient UV emission to ~350 nm (onset ~325 nm), hypsochromically shifted 20 nm relative to the TIPS-naphthalene benchmark. Demonstrated blue-to-UV UC-driven release of fluorescein from a photocage.

From the Yanai (Kyushu) and Kerzig (Mainz) groups, both leaders in TTA-UC. Pushes efficient UV upconversion (>10% QY) to 350 nm - the shortest wavelength at this efficiency level. The substituent size-activity relationship provides practical design rules. Open access via PMC.

First use of cationic chiral iridium(III) complexes as triplet sensitizers for TTA-UC, operating in R-limonene as a bio-derived green solvent. Chiral Ir(piq)2(dmbpy)+ enantiomers are soluble in R-limonene while the racemic form is not (due to higher crystallinity). Achieves 4.5% quantum yield under air with DPA as annihilator at 445 nm excitation. No stereoselectivity observed in TTA-UC despite solubility differences between enantiomers. Long alkyl chain modifications (C9, C19) on bipyridine ligands tune solubility and UC efficiency.

Three notable aspects: (1) chiral selectivity in solubility but not in TTA-UC is a curious finding, (2) R-limonene as green solvent for TTA-UC is environmentally relevant, (3) 4.5% QY under air (no deoxygenation) is practically useful. From Toho/Nihon/Ehime Universities. PCCP vol 28, pp 2806-2810.

Review comparing lanthanide-based and TTA-based upconversion strategies for solar hydrogen generation via water splitting. Discusses how TTA-UC molecular sensitizer-emitter pairs can achieve efficient upconversion at solar intensities, and summarizes recent demonstrations of TTA systems boosting H2 production and enabling overall water splitting under visible light.

Comprehensive review covering both lanthanide and TTA approaches to solar water splitting. Useful reference for application-oriented researchers. Highlights recent TTA-UC demonstrations in H2 production.

Introduces a mediator-assisted TTA-UC approach using a neutral, noncovalently linked mediator molecule to facilitate upconversion in the UV and visible regions while minimizing reabsorption losses from the annihilator. Through detailed kinetic modeling, elucidates the underlying mechanism and highlights the role of hetero-TTA (triplet-triplet annihilation between mediator and annihilator). Reports the first estimation of a hetero-TTA rate constant, finding it exceeds the homo-TTA rate by a factor of 2. Broadens the design space for TTA-UC systems beyond conventional two-component sensitizer-annihilator pairs.

Published in JACS. First quantification of hetero-TTA rate constants. The three-component mediator approach is a new design paradigm that addresses the fundamental reabsorption problem in TTA-UC. Already cited by 1 paper. Open access via PMC (PMC12593377).

Comprehensive review of TADF molecules as heavy-atom-free sensitizers for TTA-UC. TADF emitters can serve as sensitizers because they exhibit efficient ISC with minimal energy loss (small singlet-triplet gap), long triplet lifetimes, and avoid the cost and toxicity of precious metal complexes. Covers boron difluoride curcuminoids, carbazolyl dicyanobenzenes, MR-TADF sensitizers, and osmium(II) complexes in the TTA-UC context.

From the Yanai group (Kyushu University), a world leader in TTA-UC research. TADF sensitizers are one of the most promising paths to heavy-atom-free, low-cost TTA-UC. This review consolidates the rapidly growing subfield. Published in J. Photochem. Photobiol. C (volume 87, 2026).

First demonstration of InP quantum dot-sensitized TTA-UC energy driving high-energy photoreactions. Uses non-toxic InP/ZnS QDs as sensitizer and DPA as annihilator to achieve green-to-blue TTA-UC with 8.2% normalized quantum yield and 0.55 eV anti-Stokes shift. The upconverted energy drives dehalogenation of substituted aryl halides via photoredox C-C coupling in excellent yields, and radical polymerization of MMA to PMMA. TTA-UC is the sole driving force since the required reduction potential exceeds what InP QDs alone can provide. Overcomes key limitations of UV-based photochemistry.

First InP QD-sensitized TTA-UC for photocatalysis. InP QDs are non-toxic (Cd-free, Pb-free), addressing the toxicity concern of CdSe/PbS sensitizers. The demonstration of TTA-UC as the sole driving force for demanding photoredox reactions is compelling. From IISER Pune and Leibniz Institute. Open access in Chem. Sci. vol 17, pp 626-633.

Demonstrates plasmon-enhanced solid-state triplet fusion (TTA) upconversion with an ultralow excitation threshold. Uses plasmonic nanostructures to concentrate electromagnetic fields and enhance both the absorption and the triplet-triplet annihilation processes in solid-state upconversion films. Addresses one of the central challenges in solid-state TTA-UC: the high intensity thresholds required for efficient operation. The plasmonic enhancement brings the threshold down to levels compatible with unconcentrated sunlight.

Published in Nature Photonics (vol 20, pp 24-30). From Princeton (Rand group) and NC State (Castellano group), two leading labs in photon management and TTA-UC respectively. Solving the threshold problem for solid-state TTA-UC is critical for real-world solar and photocatalysis applications. The plasmon-enhanced approach is a fundamentally different strategy from molecular engineering.

Proposes and demonstrates a TTA-UC heterojunction constructed from MoS2 and ZIF-FL (a zeolitic imidazolate framework with fluorescein linkers). Achieves NIR-to-blue-violet upconversion with 0.86 eV anti-Stokes shift and excellent stability. Resonance energy transfer and interfacial migration bridges (Mo-N, Fe-S) facilitate triplet-triplet energy transfer from 3MoS2* to 3ZIF-FL*. Energy from TTA-generated singlets transfers in situ to pollutant reactants rather than emitting photons, avoiding reabsorption loss. Tetracycline removal reaches 85.4% even at 5-10 C, demonstrating genuine NIR-driven photocatalysis.

Published in Materials Horizons (vol 13, pp 1375-1392). Novel concept of TTA-UC heterojunction using inorganic/MOF materials rather than molecular sensitizer-annihilator pairs. The in-situ energy transfer to reactants (bypassing photon emission and reabsorption) is an elegant approach. Practical pollutant degradation at low temperatures demonstrates real-world applicability.

Presents a strategy to decouple the concentration dependence of TTA-UC by encapsulating ultralow-concentration sensitizer/annihilator pairs (244 nM/6.5 uM) in solid micellar nanoparticles. Achieves an exceptional 15.9% upconversion quantum efficiency (normalized to 100%) in aqueous media, surpassing reported NIR upconversion nanomaterials by two orders of magnitude. Demonstrates time-resolved temperature sensing as a practical application.

From the Ling Huang group. 15.9% QY in aqueous media at ultralow concentrations is remarkable - two orders of magnitude better than other NIR UC nanomaterials in water. The nanoconfinement strategy solves the fundamental concentration-efficiency tradeoff in TTA-UC. Published in Small Methods. Directly relevant to bioimaging and clinical diagnostics.

Comprehensive review bridging the gap between molecular design optimization and practical TTA-UC applications. Discusses application-specific requirements for designing sensitizer-annihilator pairs and provides a library of sensitizers and annihilators organized by application domain. Addresses why most applied research still relies on classical pairs (PtOEP/DPA, PdTPTBP/perylene, PdPc(OBu)8/rubrene) despite extensive optimization literature, and proposes strategies to close this gap.

Published in Coordination Chemistry Reviews (vol 548). Already cited by 4 papers within months, indicating strong community uptake. The application-oriented framing and sensitizer/annihilator library are practical reference tools for the field. From China University of Petroleum (East China).

Integrates machine learning with photophysical analysis to decode the factors governing TTA efficiency in anthracene-based systems. Maps molecular descriptors to upconversion quantum yield, enabling data-driven prediction of TTA-UC performance for new annihilator candidates. Addresses the challenge of rational molecular design by replacing trial-and-error synthesis with computational screening.

ML-driven approaches to TTA-UC design are still rare. Anthracene derivatives are the most widely used annihilator class, making this directly applicable. Aligns with the data-driven direction advocated by the Isokuortti/Nienhaus perspective in Chem. Sci. Published in J. Luminescence.

Reports a hybrid approach that encapsulates QD-sensitized TTA-UC mixtures into mesoscale droplets within a rigid acrylate matrix, preserving liquid-like dynamics in a pseudo-solid form. Using PbS quantum dot sensitizer, carboxytetracene mediator, and TES-ADT annihilator, achieves upconversion of NIR-I and NIR-II photons beyond the silicon bandgap (>1100 nm). A key advance is the rational design of a chemically compatible polymer system enabling spontaneous phase separation of QDs into nanodroplets while preserving QD surface chemistry, preventing an over 1000-fold drop in upconversion efficiency typically seen in solid-state systems.

Published in Advanced Materials. Addresses the critical solution-to-solid translation challenge for QD-sensitized TTA-UC. The pseudo-solid-state approach with polymer encapsulation is a practical route toward integration with silicon photovoltaics. Harvesting sub-bandgap photons beyond 1100 nm is directly relevant to exceeding the Shockley-Queisser limit.

Develops high-concentration annihilator systems for efficient green-to-blue TTA-UC and demonstrates their application in photocatalytic production of hydroxyl radicals. Addresses the concentration-quenching problem that typically limits annihilator loading, enabling higher UC efficiency at practical concentrations. The upconverted blue light drives photocatalytic generation of reactive oxygen species (hydroxyl radicals) for environmental applications.

Published in Dyes and Pigments (vol 249, 2026). Connects TTA-UC to practical environmental photocatalysis via hydroxyl radical production. The high-concentration annihilator strategy addresses a practical limitation. From the Ai-Guo Shen group.

Demonstrates TTA-UC as a sub-bandgap photon harvesting strategy for enhancing photoelectrochemical reactions using Mo-doped BiVO4 photoanodes. The TTA-UC film (PtOEP/DPA) converts green photons below the BiVO4 bandgap into blue photons that can be absorbed by the photoanode, boosting the photoelectrochemical water splitting performance. Extends the authors prior work on TTA-UC-enhanced photoelectrocatalytic water treatment.

Published in J. Luminescence (vol 293, 2026). Direct application of TTA-UC to photoelectrochemical solar fuel production. Practical demonstration of sub-bandgap harvesting for water splitting on BiVO4 photoanodes. From National Tsing Hua University (Taiwan).

Investigates the carrier dynamics in ZnSe quantum dot-molecule hybrid systems for efficient TTA photon upconversion using time-resolved spectroscopy. Provides spectral analysis of the energy transfer pathways from ZnSe QD sensitizers to molecular mediator/annihilator components, elucidating the roles of charge transfer and triplet energy transfer in the QD-M TTA-UC cascade. Complements the Kaifeng Wu group's work on ZnSe QD-ketone systems published in Small.

Published in Spectrochimica Acta Part A (2026). ZnSe QDs are an important low-toxicity (Cd-free, Pb-free) sensitizer class for TTA-UC. Detailed carrier dynamics studies provide the mechanistic understanding needed to optimize these systems. Directly synergistic with the Wang/Wu Small paper on ZnSe/thioxanthone already in the catalog.

Examines both singlet fission (downconversion) and triplet-triplet annihilation upconversion in dimeric tetracene complexes centered on Pt(II) and Pd(II) metal ions. Demonstrates that the same molecular system can exhibit competing SF and TTA-UC pathways depending on excitation conditions and metal center identity. Provides insights into the interplay between these two photon management processes within a single molecular architecture, informing the design of chromophores that can be tuned for either SF or TTA-UC.

Published in Adv. Funct. Mater. Already cited by 1. Bridges the singlet fission and TTA-UC communities by demonstrating both processes in one molecule. The Pt vs Pd comparison reveals how heavy-atom effects modulate the SF/TTA balance. Tetracene is a key chromophore class for both SF and TTA-UC (complementary to the Naimovicius JACS paper on DPP/DPND).

Demonstrates that ternary AgAuSe quantum dots can serve as NIR triplet sensitizers for TTA-UC through rational ligand engineering. AgAuSe QDs are a previously unexplored class of semiconductor nanocrystals for upconversion, combining the advantages of silver and gold chalcogenide compositions. Ligand engineering unlocks efficient triplet energy transfer from the QD sensitizer to molecular annihilators, enabling near-infrared-excited photon upconversion.

Published in ACS Energy Letters (vol 11, issue 1, pp 899-905). AgAuSe is a completely new QD composition for TTA-UC sensitization, expanding the materials palette beyond PbS, CdSe, InP, ZnSe, and CsPbX3 QDs already in the catalog. Ternary alloy QDs offer additional tunability. From the Qiangbin Wang group (Suzhou Institute of Nano-Tech). Directly complements the growing catalog of QD sensitizer studies.

Demonstrates blue-to-UV photon upconversion sensitized by CsPbBr3 perovskite quantum dots. Through-bond electronic coupling between surface-anchored ligands and the perovskite nanocrystal, combined with strong ligand binding, enables efficient triplet energy transfer from CsPbBr3 QDs to UV-emitting annihilators. Extends perovskite-sensitized TTA-UC into the challenging blue-to-UV spectral direction, where the large energy gap between sensitizer absorption and annihilator emission demands precise energy level alignment.

Published in ACS Energy Letters 2026. Co-authored by Isokuortti and Nienhaus (Rice, authors of the Chem. Sci. solid-state annihilator perspective and the Chem. Rev. perovskite sensitizer review). Also involves the Page group (UNC, TTA-UC 3D printing). Through-bond coupling is a key mechanistic insight for optimizing perovskite-to-molecule energy transfer. Blue-to-UV is an underexplored spectral direction for perovskite-sensitized TTA-UC.

Demonstrates that micro-cocrystals of the intermolecular charge-transfer complex formed from pyrene and tetracyanobenzene undergo ISC of the directly excited CT exciton, yielding triplet CT states. These triplets efficiently transfer to a DPA-based acceptor at the cocrystal interface, enabling solid-state TTA-UC without any heavy-atom-containing sensitizer. This establishes a new heavy-atom-free sensitization paradigm using organic donor-acceptor cocrystals.

Published in JACS (vol. 147, issue 52). First demonstration of TTA-UC sensitized by intermolecular charge-transfer cocrystal ISC. Completely heavy-atom-free. Complements the Klein et al. BHJ CT-state sensitization approach with a crystalline, well-defined counterpart. Opens a new class of ordered solid-state sensitizers for TTA-UC.

Demonstrates that direct charge-transfer (CT) transitions in 2D organic-inorganic hybrid perovskites can drive triplet generation and photon upconversion, bypassing conventional energy transfer pathways. The below-gap CT transition at the organic-inorganic interface directly populates triplet states on the organic chromophore spacers, enabling TTA-based upconversion. This mechanism is fundamentally different from the Dexter-type triplet energy transfer or charge-separation-mediated sensitization previously observed in perovskite-sensitized systems.

Published in JACS (vol 147, issue 51, pp 47280-47288). From the Haiming Zhu group (Zhejiang University). Establishes a new mechanistic pathway for perovskite-sensitized TTA-UC via direct CT transitions, distinct from Dexter transfer. Complements the VanOrman Chemical Reviews perovskite sensitizer review, the Sloane 2D perovskite spacer paper, and the Wu CsPbBr3 paper already in the catalog. The below-gap excitation capability could extend the spectral range accessible to perovskite-sensitized upconversion.

Comprehensive review on strategies for constructing oxygen-tolerant TTA-UC materials, addressing the critical challenge of molecular oxygen quenching triplet states. Covers three main approaches: (1) molecular engineering with electron-deficient groups and conformational control to improve chromophore photostability, (2) fabrication of oxygen-resistant TTA-UC nanoparticles using reductive oil droplets as soft templates, and (3) nanostructure-mediated optimization of intermolecular triplet energy transfer dynamics for enhanced oxygen resilience. Also discusses future integration of TTA-UC with synthetic biology to design biosynthetic upconversion proteins.

From Nankai University (Research Center for Analytical Sciences). Oxygen quenching is arguably the single biggest practical barrier to real-world TTA-UC applications. This review consolidates the rapidly growing toolkit for oxygen tolerance. The synthetic biology angle (biosynthetic upconversion proteins) is forward-looking. Open access. Published in Synth. Biol. Eng. 2026, 4(1), 10021. 222 downloads, 2289 views already.

Demonstrates that intramolecular triplet-triplet annihilation in appropriately designed annihilator dimers or oligomers significantly enhances photon upconversion performance under far-red light excitation. By covalently linking annihilator units, the intramolecular TTA pathway circumvents the diffusion bottleneck that limits bimolecular TTA, particularly important at the far-red excitation wavelengths where sensitizer triplet lifetimes are shorter. Extends the Ling Huang group's systematic work on TTA-UC efficiency optimization and far-red/NIR photon harvesting.

Published in JPCL vol 16, issue 51, pp 13182-13189 (December 2025). From the Ling Huang group (CCNU), one of the most prolific TTA-UC labs. Intramolecular TTA is a key strategy for solid-state and diffusion-limited systems. Far-red excitation is practically important for biological and solar applications. Complements the Kobori vibronic trimer paper (intramolecular hopping) already in the catalog.

Comprehensive Accounts of Chemical Research review covering the evolution of TTA-UC from molecular systems to functional materials. Covers nanoparticle-based platforms, soft core-shell nanostructures for water-dispersible TTA-UC, and protein-integrated assembly processes. Provides a roadmap for translating molecular-level TTA-UC understanding into practical materials for applications in solar energy, bioimaging, photocatalysis, and sensing.

Published in Accounts of Chemical Research (vol 58, issue 24, pp 3543-3557) from the Ling Huang group (Central China Normal University), one of the most prolific TTA-UC labs globally. Accounts reviews are invitation-only and represent the definitive summary of a group's research program. The Huang group has multiple papers in our catalog (Se-cyanine sensitizer, BODIPY ligand QD, nanoconfinement, color-tunable) - this review provides the unifying framework.

Comprehensive Chemical Reviews article on the emergence of halide perovskite materials (both nanocrystal and bulk forms) as a new class of triplet sensitizers for TTA-based photon upconversion. Covers CsPbX3 nanocrystals, MAPbI3 and mixed-halide bulk perovskites, 2D Ruddlesden-Popper perovskites, and lead-free alternatives. Discusses triplet generation mechanisms at the perovskite-organic interface (Dexter-type triplet transfer vs charge-transfer-mediated sensitization), the role of surface chemistry and passivation in triplet transfer efficiency, and applications in solar energy harvesting, photocatalysis, and bioimaging. Provides a roadmap for overcoming current limitations including oxygen sensitivity, interfacial engineering challenges, and the need for lead-free compositions.

Published in Chemical Reviews (vol 125, issue 23, pp 11426-11460), the highest-impact review journal in chemistry. Co-authored by Isokuortti and Nienhaus (Rice University), who also authored the solid-state annihilator design perspective already in the catalog. This is the definitive review on perovskite-sensitized TTA-UC, consolidating a rapidly growing subfield. Directly complements the Sloane et al. 2D perovskite spacer paper and the Klein et al. BHJ CT-state sensitizer paper in the catalog.

Demonstrates homomolecular photon upconversion in a perylene-decorated iron(III) complex, where the Fe(III) center acts as both triplet sensitizer and the perylene moieties serve as annihilators in the same molecular construct. This self-contained TTA-UC system eliminates the need for separate sensitizer and annihilator components, simplifying device design. Builds on the group's prior work on Fe(III) complexes with 100 ns lifetimes. Homomolecular TTA-UC avoids the diffusion limitations of bimolecular solution-phase systems.

Published in JACS (vol 147, issue 46, pp 43013-43028) from the Wenger group. The self-contained Fe(III)-perylene architecture is elegant: earth-abundant sensitizer + well-known annihilator in a single molecule. Homomolecular UC eliminates the sensitizer-annihilator encounter problem. Extends the earth-abundant iron paradigm to practical TTA-UC demonstration.

Demonstrates an all-passive upconversion imaging system that converts low-intensity incoherent NIR light (down to ~10^-6 W/cm^2 across a 23 mm aperture) into visible light perceptible by the human eye, with no external power input. Three key innovations: (1) TTA-UC via a Y6/rubrene bulk heterojunction, (2) plasmonic enhancement of absorption and field intensity, (3) collection enhancement using a dichroic thin-film assembly. Integrated into a dual-wavelength telescope for high-resolution imaging, preserving ray directionality between NIR input and visible output.

Published in Adv. Funct. Mater. From the Congreve (Stanford) and Kats (Wisconsin-Madison) groups. All-passive operation at 10^-6 W/cm^2 is extraordinary - orders of magnitude below solar intensity. The combination of TTA-UC + plasmonics + photonic engineering is a tour de force. Directly synergistic with the Wisch et al. Nature Photonics plasmon-enhanced paper already in the catalog. Practical implications for night vision, low-light sensing, and defense.

Demonstrates a photon-multiplier luminescent solar concentrator (PM-LSC) utilizing singlet fission (SF) as the photon multiplication mechanism. SF chromophores in the LSC absorb one photon and generate two triplet excitons, which then emit as two lower-energy photons guided to edge-mounted solar cells. This achieves over 100% internal photoluminescence quantum efficiency, bypassing the thermodynamic free energy losses that limit conventional LSCs. Directly bridges the singlet fission and photon management communities.

Published in Nano Letters (vol 25, issue 45, pp 16204-16211). From the Rao group at Cambridge, leaders in singlet fission research. SF is the reverse of TTA - materials that undergo efficient SF are prime candidates as TTA-UC annihilators (the Naimovicius JACS paper demonstrated this directly). SF-LSCs and TTA-UC-LSCs are complementary photon management strategies for photovoltaics. New SF chromophores developed for LSCs could be repurposed as TTA-UC annihilators.

Presents a multilayer molecular system where charge transfer (CT) states in a squaraine (DIB-SQ):PCBM donor-acceptor bulk heterojunction serve as NIR photosensitizer for solid-state TTA-UC. Fine-tuning PCBM loading engineers charge transfer states of triplet character (3CT) that facilitate triplet generation. At optimized 1:3 blend ratio with a rubrene/DBP annihilator layer, achieves 1.36% upconversion quantum yield at 690 nm excitation with a significantly low intensity threshold for the linear regime.

Introduces charge transfer states as a new sensitization pathway for solid-state TTA-UC, distinct from conventional molecular or QD sensitizers. The squaraine:PCBM architecture leverages organic photovoltaic device physics for upconversion. Time-resolved spectroscopy and magnetic field-dependent PL provide mechanistic detail. Preprint from University of Queensland. UPDATE 2026-03-15: Now published in Advanced Materials Interfaces (doi: 10.1002/admi.202500897).

Demonstrates that triplet-triplet annihilation upconversion (TTA-UC) offers a scalable, low-power alternative to ultrafast laser-based two-photon lithography for nanofabrication. The quadratic intensity dependence of TTA-UC provides inherent optical confinement similar to two-photon absorption but at orders-of-magnitude lower power and with CW excitation. Achieves sub-wavelength feature resolution relevant to plasmonics, nanophotonics, and biomedical applications. Addresses the scaling bottleneck of conventional two-photon approaches by replacing expensive femtosecond lasers with simple CW sources.

From the Congreve lab (Stanford), leaders in TTA-UC applications. Extends TTA-UC into precision nanofabrication, complementing the O'Dea et al. vat-based 3D printing and the Kuhl et al. direct laser writing papers already in the catalog. The low-power, CW-excitation advantage directly addresses manufacturing scalability. Preprint on arxiv, not yet journal-published.

Demonstrates NIR-to-visible photon upconversion using gold quantum rods as triplet sensitizers, and couples the upconverted light to drive aqueous photo-driven polymerization. Gold quantum rods (distinct from the Au42 nanoclusters already in the catalog) represent a shape-controlled class of gold nanostructures for TTA-UC sensitization. The aqueous-phase demonstration addresses the practical challenge of performing TTA-UC in water, relevant to biological and green chemistry applications. From the Rongchao Jin group (Carnegie Mellon) and Matyjaszewski group (pioneer of ATRP polymerization).

Published in JACS (vol 147, issue 31, pp 28241-28250). Gold quantum rods join Au42 nanoclusters (Mitsui, Angew. Chem., already in catalog) as a second gold nanostructure morphology for TTA-UC sensitization. The shape-property relationship in gold nanostructures for triplet sensitization is a new frontier. Aqueous polymerization driven by upconverted light extends the Hubner et al. Adv. Opt. Mater. work. From two powerhouse groups at Carnegie Mellon.

Comprehensive review systematically summarizing three roads to large anti-Stokes shifts in TTA-UC: (i) reduce ISC energy loss using photosensitizers with small S1/T1 gaps (charge-transfer TADF, multi-resonance, direct S0-T1 excitation, minimal exchange splitting in inorganics), (ii) reduce triplet energy transfer loss by energy-matched sensitizer-annihilator selection, and (iii) reduce TTA process energy loss by regulating singlet/triplet energy levels of the annihilator. Also covers representative applications in life science, photocatalysis, and 3D printing.

Published in ACS Nano (vol 19, issue 28, pp 25596-25616). Comprehensive review that provides a systematic framework for understanding and optimizing anti-Stokes shifts. Covers TADF, multi-resonance, direct S0-T1, and inorganic sensitizer strategies. Complements the Liu et al. Coord. Chem. Rev. molecular design review already in the catalog.

Achieves TTA-UC into the UVC spectral region using TIPS-benzene derivatives as annihilators paired with a heptazine derivative as the triplet sensitizer. The heptazine absorbs in the visible/UVA region and has a triplet energy level high enough to sensitize the TIPS-benzene emitters. Bulky TIPS substituents suppress aggregation-induced deactivation of the benzene-based annihilators, maintaining high emission efficiency. Pushes the frontier of TTA-UC emission wavelengths into the germicidal UVC range (200-280 nm), relevant to sterilization and surface decontamination applications.

From the Yanai group (Kyushu University), world leaders in TTA-UC. UVC generation via TTA-UC is an extreme spectral challenge requiring very high triplet energies and precise energy alignment. TIPS-benzene is a new annihilator class for UVC emission, and heptazine derivatives are a new sensitizer class. Complements the Moghtader TIPS-biphenyl paper (UV, ~350 nm) by pushing deeper into the UV. Published in Adv. Opt. Mater. vol 13, 2025.

Designs a trimeric annihilator with three anthracene units arranged around a central boron atom. The vibronic coupling in this architecture accelerates intramolecular triplet-exciton hopping, yielding a 20% faster TTA rate compared to dimeric analogs. The rapid hopping increases the effective interaction volume for TTA during molecular collisions, improving the probability of productive annihilation events. Viscosity-dependent luminescence tunability opens applications in cellular microenvironment sensing.

Published in Angewandte Chemie (Kobe University). Intramolecular TTA circumvents the diffusion bottleneck of intermolecular TTA. The trimer-around-boron architecture is a new molecular topology for intramolecular UC. The 20% TTA rate enhancement is modest but the design principle (vibronic hopping acceleration) is generalizable.

Introduces 5,11-di(thiophen-2-yl)tetracene (DTTc) as a novel tetracene derivative optimized for efficient singlet fission in thin films with significantly enhanced physical and chemical stability compared to parent tetracene. The thienyl groups at the 5,11-positions provide electronic tuning while improving processability and ambient stability. As a singlet fission chromophore, DTTc is a prime candidate for repurposing as a TTA-UC annihilator, since SF and TTA are reverse processes operating on the same energetic landscape.

Published in Adv. Funct. Mater. vol 35, issue 42, 2025. From Seoul National University. Tetracene derivatives are already established TTA-UC annihilators (e.g., TES-ADT, carboxytetracene in the Congreve group's work). A more stable tetracene derivative with tuned electronic properties expands the annihilator toolkit. The enhanced ambient stability directly addresses the degradation challenge in solid-state TTA-UC devices. SF efficiency indicates favorable triplet energetics for TTA.

Addresses the parasitic back energy transfer problem in thin-film TTA-UC bulk heterojunctions. Back energy transfer from the annihilator singlet state to the sensitizer acts as a fundamental loss channel in solid-state TTA-UC devices. The authors demonstrate strategies to alleviate this parasitic process, enhancing overall thin film upconversion efficiency. Complements the Gou et al. (solution-phase) and Sloane et al. (perovskite spacer) approaches to addressing back transfer.

From the Congreve lab (Stanford) with Kats and Jaramillo collaborators. Published in Adv. Opt. Mater. vol 13, issue 17. Directly tackles the back energy transfer problem that is one of the key efficiency-limiting mechanisms in solid-state TTA-UC. Synergistic with the Sloane et al. 2D perovskite spacer paper already in the catalog.

Investigates intramolecular triplet-triplet annihilation upconversion facilitated by double sensitization, where two sensitizer molecules simultaneously provide triplet excitons to a single annihilator dimer/oligomer. From the Chihaya Adachi group at Kyushu University (TADF pioneers). Establishes that double sensitization of intramolecular TTA dimers provides a pathway to overcome the statistical limitation of requiring two triplet excitons on a single annihilator scaffold. Mechanistic insights on how the double sensitization rate depends on sensitizer concentration and excited state dynamics.

Published in JPCL vol 16, issue 20, pp 5173-5179 (May 2025). From the Adachi group at Kyushu University, pioneers of TADF and contributors to the RISC-based upconversion approach (Kohata et al. Angew. Chem. already in catalog). Double sensitization of intramolecular TTA is a novel mechanistic study that informs the design of self-contained TTA-UC molecular systems.

Introduces a BNOSe (boron-nitrogen-oxygen-selenium) heterocyclic compound as a new class of heavy-atom-free triplet sensitizer for TTA-UC, achieving multichromatic anti-Stokes emission. The optimized system converts deep-red light (640 nm) into simultaneous dual emissions at 617 nm (orange) and 412 nm (blue), achieving a record TTA-UC quantum yield of 19.3% with a 1.07 eV anti-Stokes shift - the largest reported for an all-organic sensitizer system. The selenium atom provides spin-orbit coupling for ISC without requiring precious metals.

Record 19.3% QY with 1.07 eV anti-Stokes shift for an all-organic system. BNOSe heterocycles are a genuinely new sensitizer class - distinct from BODIPY, porphyrin, cyanine, and TADF sensitizers. Multichromatic (dual-wavelength) upconversion emission is unusual and could enable multiplexed sensing or dual-band photocatalysis. Published in JPCL (vol 16, issue 17, pp 4270-4276).

Presents an automated, high-throughput platform for discovery and optimization of TTA-UC systems. Performs 100 concentration scans in two hours under oxygen-free conditions, generating comprehensive concentration maps of quantum yield, triplet energy transfer efficiency, and threshold intensity. Identifies key loss mechanisms: sensitizer triplet self-quenching via aggregation, sensitizer-TTA at high porphyrin concentrations, and reverse triplet energy transfer (RTET) increasing losses and thresholds at elevated sensitizer levels. Tests novel sensitizer-annihilator pairs confirming these loss mechanisms. A powerful tool for advancing TTA-UC research methodology.

Published in ACS Central Science (vol 11, issue 3, pp 413-421). First self-driving laboratory platform specifically for TTA-UC optimization. Aligns with the data-driven/ML direction advocated by the Isokuortti/Nienhaus perspective and the Aydemir ML paper. From Universitat Politecnica de Catalunya, Vilnius University, and ICMAB-CSIC Barcelona. Open access via PMC (PMC11950846). Identifies fundamental loss mechanisms that inform molecular design strategies.

Reports iron(III) complexes with luminescence lifetimes up to 100 ns, specifically designed to enhance photon upconversion and photocatalysis. Iron is earth-abundant and non-toxic, making these complexes a sustainable alternative to precious-metal (Ru, Ir, Pt, Pd) sensitizers. The 100 ns lifetime is exceptional for Fe(III) complexes and enables efficient triplet energy transfer to acceptors for TTA-UC and driving challenging photocatalytic transformations.

Published in JACS (vol 147, issue 10, pp 8760-8768) from the Wenger group (Basel). Earth-abundant iron sensitizers with 100 ns lifetimes are a major breakthrough for sustainable TTA-UC. Complements the Jin et al. ACS Catal. iron sensitizer paper already in the catalog. The Wenger group is the leading lab in iron-based photochemistry for upconversion. This paper lays the groundwork for the homomolecular Fe(III)-perylene UC paper also from the same group.

Proposes an alternative photon upconversion mechanism using reverse intersystem crossing (RISC) in thermally activated delayed fluorescence (TADF) molecules. Combines the triplet sensitizer Ir(ppy)3 with the TADF molecule CzBSe: the sensitizer absorbs light, generates a triplet, and transfers it to the TADF molecule via Dexter-type triplet energy transfer. The TADF molecule then undergoes RISC to convert the triplet back to a singlet, emitting anti-Stokes photons with 0.18 eV upshift. This is a fundamentally different PUC mechanism from TTA-UC but shares the same triplet sensitization step.

From the Adachi group (Kyushu University), pioneers of TADF and organic electronics. Demonstrates a new single-molecule photon upconversion pathway that bypasses the need for bimolecular TTA entirely. The triplet energy transfer rate depends strongly on the TADF molecule's triplet radiative decay rate and Gibbs energy difference between donor and acceptor. Published in Angew. Chem. (vol 64, issue 7). Key implication for TTA-UC: TADF molecules with efficient RISC could serve dual roles as both TTA-UC annihilators AND standalone RISC-based upconverters.

Proposes a novel organic radical donor-triplet acceptor dyad (TTM-Cz-Per) for photon upconversion via doublet spin states. The stable organic radical TTM-Cz serves as donor, linked to a perylene (Per) acceptor. Upon red excitation, doublet-to-triplet energy transfer (DTET) occurs from the radical donor to the acceptor, generating the perylene triplet state (97 ns lifetime) which then undergoes TTA to produce upconverted 490 nm emission. The CT character is confined within the donor moiety, circumventing competing charge transfer dynamics. Computational results confirm intramolecular DTET via quartet state analysis.

Published in JACS (vol 147, issue 1, pp 1017-1027). First demonstration of doublet-mediated TTA-UC in a radical-acceptor dyad. This represents a paradigm shift: organic radicals with doublet ground states bypass the ISC bottleneck entirely since the radical already has an unpaired electron. Opens a new class of heavy-atom-free sensitizers for TTA-UC. The TTM-Cz radical is well-characterized and commercially relevant.

Demonstrates green-to-blue solid-state TTA-UC in hydrogen-bonded organic frameworks (HOFs), a new class of porous crystalline materials distinct from MOFs and COFs. Uses zinc tetrakis(4-carboxyphenyl)porphyrin (Zn-TCPP) as sensitizer and dipyridyl thiazolothiazole (TzBIPY) as annihilator, co-assembled via hydrogen bonding. HOFs offer advantages over MOFs and COFs including mild synthesis conditions, solution processability, self-healing capability, and reversible assembly. Addresses the efficiency gap between solution-phase and solid-state TTA-UC by leveraging the ordered chromophore arrangement within the HOF lattice.

HOFs are a genuinely new framework class for TTA-UC, complementing the MOF, COF, zeolite, and PAF approaches already in the catalog. The hydrogen-bonding assembly strategy offers milder conditions than the covalent (COF) or coordination (MOF) approaches. ChemRxiv preprint - not yet journal-published as of March 2026. Less impact than the COF papers in Chem and Angew. Chem. but expands the materials palette.