Triplet Energy Transfer Research Articles

Unveiling the Triplet-State Interaction Mechanism Between 4-Carboxybenzophenone and 2-Naphthalene Sulfonate—A Laser Flash Photolysis Study

This communication aims to comprehensively elucidate the intricate mechanism governing the interaction between the excited triplet state of 4-Carboxybenzophenone (CB*) and the anionic form of 2-Naphthalene Sulfonate (NpSO3−), employing the 337 nm Nanosecond Laser Flash Photolysis technique for this investigation. When the CB is selectively excited by a 337 nm laser, two primary processes become possible: (i) energy transfer from 3CB* to NpSO3− and (ii) electron transfer from NpSO3− to 3CB*. The dynamics of these interactions are explored through experimental observations of transient absorption spectra and the analysis of respective kinetic traces. The primary process dominating in the 3(CB...NpSO3−)* system is identified as triplet energy transfer from excited 3CB* to 3(NpSO3−), as demonstrated by characteristic spectral features observed at 410–420 nm. Comparisons are made with a similar system studied by Yamaji and co-workers, 3(BP•−...NpO•)*, revealing differences in the priority of primary process occurrences. These findings contribute to a deeper understanding of the intricate interactions between excited molecules and ground-state donors, aiding in the comprehension of mechanisms governing these reactions.

Steering Energy Transfer Pathways through Mn-Doping in Perovskite Nanocrystals.

Modulation of singlet and triplet energy transfer from excited semiconductor nanocrystals to attached dye molecules remains an important criterion for the design of light-harvesting assemblies. Whereas one can consider the selection of donor and acceptor with favorable energetics, spectral overlap, and kinetics of energy transfer as a means to direct the singlet and triplet energy transfer pathways, it is not obvious how to control the singlet and triplet characteristics of the donor semiconductor nanocrystal itself. By doping CsPb(Cl0.7Br0.3)3 nanocrystals with Mn2+, we have now succeeded in increasing the triplet characteristics of semiconductor nanocrystals. The singlet and triplet energy transfer between excited Mn-CsPb(Cl0.7Br0.3)3 nanocrystals and a cyanine dye (4,5-benzoindotricarbocyanine) show the participation of band gap states in singlet energy transfer and Mn2+-activated states in triplet energy transfer. By tracking donor and acceptor emission as well as transient absorption spectral features, we were able to distinguish the two independent energy transfer pathways. Whereas singlet energy transfer from the exciton emission band remains unchanged (2%), increasing the concentration of Mn2+ in perovskite nanocrystals results in an increase of triplet energy transfer yield up to 17.5%. The ability to enhance the triplet transfer yield in CsPb(Cl0.7Br0.3)3 nanocrystals through Mn-doping opens up new opportunities to develop optoelectronic and display devices.

Photodegradation reveals that singlet energy transfer impedes energy-gradient-driven singlet fission in polyacene blends.

Singlet fission (SF) is a process that is potentially beneficial for photovoltaics by producing two triplet excitons from a single photon, but its application is often hindered by the inability to effectively separate the resultant triplet excitons. It has been proposed that an energy gradient can assist in separating triplet excitons through triplet energy transfer between chromophores of different triplet energies, but this approach has only been studied in solution and the efficacy of this strategy in the solid state is under explored. Here, we investigate energy-gradient-driven SF in a disordered solid state, in the form of suspensions of 5,12-bis(triisopropylsilylethnyl)tetracene:6,13-bis(triisopropylsilylethnyl)pentance (TIPS-Tn:TIPS-Pn) blend nanoparticles (NPs). Rather than using more conventional techniques such as ultrafast (sub-nanosecond) spectroscopy, we study the photophysics in these NPs through monitoring their photodegradation. TIPS-Tn photodegrades rapidly in neat NPs, but this photodegradation is suppressed upon the addition of TIPS-Pn, indicating a decrease in the TIPS-Tn triplet population. By modeling the photodegradation over a timescale of minutes to hours, we are able to reveal details of processes on the ultrafast timescale. We show that triplet energy transfer occurs from TIPS-Tn to TIPS-Pn, leading to slower photodegradation for TIPS-Tn, and faster photodegradation for TIPS-Pn. However, modeling additionally indicates that singlet energy transfer from TIPS-Tn to TIPS-Pn also occurs, and in fact acts to reduce the efficiency of TIPS-Tn SF. Hence, in this particular system, the energy gradient impedes SF, rather than assisting it. These findings indicate that chromophore pairs must be carefully selected to switch off singlet energy transfer for the energy-gradient approach to be effective in enhancing SF.

Fabrication of multimodal optical imaging agents through direct triplet energy transfer from rare-earth doped nanoparticles

Fabrication of multimodal optical imaging agents through direct triplet energy transfer from rare-earth doped nanoparticles

Ligand Triplet Energy Transfer from Perylene Diimide Derivatives to PbS Quantum Dots in Solution

Ligand Triplet Energy Transfer from Perylene Diimide Derivatives to PbS Quantum Dots in Solution

Recent Advances in Diphenylmethanone Oxime Reagent Chemistry for Unsaturated Bond Bifunctionalization via Energy Transfer Catalysis

The concurrent installation of C‐X (C, O, S, N) and C‐N bonds across unsaturated bond skeletons is an effective strategy for the preparation of ubiquitous motifs in pharmaceuticals and bioactive compounds. In recent years, the rapid development of bifunctionalization reactions has resulted in the emergence of bifunctional reagents as a research hotspot in this field. Among these, diphenylmethanone oxime reagents with highly active N‐O bonds featuring low dissociation energy have significantly advanced the research of bifunctionalization. These reagents possess special features to simultaneously form two chemical bonds or introduce two functional groups, which not only streamlines synthetic pathways but also enhances synthetic efficiency, displaying an excellent atom‐ and step‐economy. In addition, diphenylmethanone oxime reagents have been extensively employed in organic synthesis, attributed to their ability to facilitate the construction of complex organic structures and to provide innovative reaction pathways. In this review, we present a comprehensive overview of various diphenylmethanone oxime reagents and their applications in the bifunctional modification of unsaturated bonds through visible‐light‐mediated triplet–triplet energy transfer catalysis (TTEnT).

Triplet Energy Transfer and Photon Upconversion from Metal Nanocluster with Near‐Unity NIR Emission Quantum Yield

Triplet Energy Transfer and Photon Upconversion from Metal Nanocluster with Near‐Unity NIR Emission Quantum Yield

Anti-Stokes Emission Utilizing Reverse Intersystem Crossing.

Photon-upconversion (PUC) processes in organic molecular systems, such as triplet-triplet upconversion and hot-band absorption, are promising technologies for future energy harvesting. Although these processes can generate high-energy excitons compared to excitation energy, a PUC process with a high yield and no energy loss has not been established and, therefore, is highly desired. Here, we propose an alternative PUC mechanism that uses reverse intersystem crossing on thermally activated delayed fluorescence (TADF) molecules. This process combines a triplet sensitizer and a TADF molecule, generating a triplet in the former and transferring it to the latter. Specifically, the triplet energy transfer from Ir(ppy)3 (sensitizer) to CzBSe (TADF) results in anti-Stokes emission with an anti-Stokes energy of 0.18 eV. We found that the triplet energy transfer rate strongly depends on the triplet radiative decay rate of TADF molecules and the difference in Gibbs energy between the energy acceptor and donor. Our findings will contribute to understanding triplet energy transfer dynamics in organic energy donor-acceptor systems and will lead to various applications, such as future optical cooling systems.

Improved Functionality of Ultrafast Responsive Electrochemiluminescent Device with DNA/Ru(bpy)3 2+ Hybrid Film and Various Electrolyte Compositions

Electrochemiluminescence (ECL), a light-emitting phenomenon induced by electrochemical redox reactions, has potential applications in lightweight and flexible light-emitting devices. Previously, an ultrafast ECL response of <100 μs was successfully achieved under application of alternating current voltage by using a DNA-modified electrode including Ru(bpy)3 2+, an orange ECL material. In this study, we investigated effect of electrolyte composition on the fast responsive ECL in the DNA/Ru(bpy)3 2+ hybrid film-based ECL device. As a result, the ECL intensity and lifetime of ECL were improved by introducing additional Ru(bpy)3 2+ into the electrolyte solution. The increase concentration of Ru(bpy)3 2+ inhibited dissolution of aggregated part formed on DNA/Ru(bpy)3 2+ hybrid film and increase in the amount of reactive charge in the aggregated part. Furthermore, we introduced blue-luminescent 9,10-diphenylanthracene (DPA) into the electrolyte solution of the ECL device consisting of DNA/Ru(bpy)3 2+ hybrid film. Consequently, blue ECL from DPA was obtained from the DNA/Ru(bpy)3 2+ hybrid electrode at lower applied voltage than that required to induce the redox reactions of DPA itself. This lower-voltage-drivable blue ECL was attributed to triplet–triplet energy transfer from Ru(bpy)3 2+ in the DNA/Ru(bpy)3 2+ hybrid electrode followed by a triplet–triplet annihilation upconversion reaction of DPA in the electrolyte solution. Moreover, ultrafast-response, electrochemically triggered blue luminescence from DPA was successfully observed.

Efficient Near‐Infrared to Blue Photon Upconversion by Ultrafast Spin Flip and Triplet Energy Transfer at Organic/2D Semiconductor Interface

AbstractSolid state photon upconversion by triplet‐triplet annihilation (TTA), particularly near‐infrared (NIR)‐to‐blue upconversion, holds instant promise for enhancing optoelectronic and photochemical applications. Despite extensive studies, NIR‐to‐blue upconversion has remained particularly challenging and elusive due to inherent multiple energy‐downhill processes in TTA upconversion. In this study, using atomically thin two dimensional (2D) monolayer semiconductor as a triplet sensitizer, we demonstrate an efficient and robust solid‐state NIR‐to‐blue photon upconversion system. The ultrathin and flexible organic/2D bilayer heterostructure exhibits a NIR‐to‐blue upconversion with high quantum yield (ΦUC=1.2 %, out of 50 %), low threshold power density (Ith=110 mW/cm2) and a record‐high apparent anti‐Stokes shift of 1.12 eV. Further spin‐ and time‐resolved spectroscopy reveals an ultrafast (&lt;500 fs) electron spin flip to triplet‐like excitons in semiconductor sensitizer and subsequent picosecond (~6×1010 s−1) interfacial Dexter energy transfer to annihilator molecules. The triplet energy transfer rate and efficiency depend strongly on driving force, exhibiting Marcus normal region behavior. This work demonstrates 2D monolayer semiconductor as a superior ultrathin light harvesting and triplet sensitization layer and reveals the key knob to overcome the compromise between upconversion efficiency and energy loss, offering a viable pathway to efficient solid state NIR‐to‐blue photon upconversion and implementation.

Efficient Near-Infrared to Blue Photon Upconversion by Ultrafast Spin Flip and Triplet Energy Transfer at Organic/2D Semiconductor Interface.

Solid state photon upconversion by triplet-triplet annihilation (TTA), particularly near-infrared (NIR)-to-blue upconversion, holds instant promise for enhancing optoelectronic and photochemical applications. Despite extensive studies, NIR-to-blue upconversion has remained particularly challenging and elusive due to inherent multiple energy-downhill processes in TTA upconversion. In this study, using atomically thin two dimensional (2D) monolayer semiconductor as a triplet sensitizer, we demonstrate an efficient and robust solid-state NIR-to-blue photon upconversion system. The ultrathin and flexible organic/2D bilayer heterostructure exhibits a NIR-to-blue upconversion with high quantum yield (ΦUC = 1.2%, out of 50%), low threshold power density (Ith = 110 mW/cm2) and a record-high apparent anti-Stokes shift of 1.12 eV. Further spin- and time-resolved spectroscopy reveals an ultrafast (< 500 fs) electron spin flip to triplet-like excitons in semiconductor sensitizer and subsequent picosecond (~ 6×1010 s-1) interfacial dexter energy transfer to annihilator molecules. The triplet energy transfer rate and efficiency depend strongly on driving force, exhibiting Marcus normal region behavior. This work demonstrates 2D monolayer semiconductor as a superior ultrathin light harvesting and triplet sensitization layer and reveals the key knob to overcome the compromise between upconversion efficiency and energy loss, offering a viable pathway to efficient solid state NIR-to-blue photon upconversion and implementation.

Nanohoops Favour Light‐Induced Energy Transfer over Charge Separation in Porphyrin/[10]CPP/Fullerene Rotaxanes

Abstract[2]Rotaxanes offer unique opportunities for studying and modulating charge separation and energy transfer, because the mechanical bond allows the robust, yet spatially dynamic tethering of photoactive groups. In this work, we synthesized [2]rotaxane triads comprising a central (aza)[10]CPP⊃C60 bis‐adduct complex and two zinc porphyrin stoppers to address how the movable nanohoop affects light‐induced charge separation and energy transfer between the rotaxane subcomponents. We found that neither the parent nanohoop [10]CPP nor its electron‐deficient analogue aza[10]CPP actively participate in charge separation. In contrast, the nanohoops completely prevented through‐space charge separation. This result is likely due to supramolecular “shielding”, because charge separation was observed in the thread that acted as reference dyad. On the other hand, the suppression of electron transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 μs. The presence of the interlocked nanohoops therefore leads to a dramatic switch between charge separation and energy transfer. We suggest that our results explain observations made by others in photovoltaic devices comprising nanohoops and may pave the way toward strategic uses of mechanically interlocked architectures in devices that feature (triplet) energy transfer.

Nanohoops Favour Light-Induced Energy Transfer over Charge Separation in Porphyrin/[10]CPP/Fullerene Rotaxanes.

[2]Rotaxanes offer unique opportunities for studying and modulating charge separation and energy transfer, because the mechanical bond allows the robust, yet spatially dynamic tethering of photoactive groups. In this work, we synthesized [2]rotaxane triads comprising a central (aza)[10]CPP⊃C60 bis-adduct complex and two zinc porphyrin stoppers to address how the movable nanohoop affects light-induced charge separation and energy transfer between the rotaxane subcomponents. We found that neither the parent nanohoop [10]CPP nor its electron-deficient analogue aza[10]CPP actively participate in charge separation. In contrast, the nanohoops completely prevented through-space charge separation. This result is likely due to supramolecular "shielding", because charge separation was observed in the thread that acted as reference dyad. On the other hand, the suppression of electron transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 μs. The presence of the interlocked nanohoops therefore leads to a dramatic switch between charge separation and energy transfer. We suggest that our results explain observations made by others in photovoltaic devices comprising nanohoops and may pave the way toward strategic uses of mechanically interlocked architectures in devices that feature (triplet) energy transfer.

Visualizing Triplet Energy Transfer in Organic Near-Infrared Phosphorescent Host-Guest Materials.

Limited by the energy gap law, purely organic materials with efficient near-infrared room temperature phosphorescence are rare and difficult to achieve. Additionally, the exciton transition process among different emitting species in host-guest phosphorescent materials remains elusive, presenting a significant academic challenge. Herein, using a modular nonbonding orbital-π bridge-nonbonding orbital (n-π-n) molecular design strategy, we develop a series of heavy atom-free phosphors. Systematic modification of the π-conjugated cores enables the construction of a library with tunable near-infrared phosphorescence from 655 to 710 nm. These phosphors exhibit excellent performance under ambient conditions when dispersed into a 4-bromobenzophenone host matrix, achieving an extended lifetime of 11.25 ms and a maximum phosphorescence efficiency of 4.2 %. Notably, by eliminating the interference from host phosphorescence, the exciton transition process in hybrid materials can be visualized under various excitation conditions. Spectroscopic analysis reveals that the improved phosphorescent performance of the guest originates from the triplet-triplet energy transfer of abundant triplet excitons generated independently by the host, rather than from enhanced intersystem crossing efficiency between the guest singlet state and the host triplet state. The findings provide in-depth insights into constructing novel near-infrared phosphors and exploring emission mechanisms of host-guest materials.

Twisted Benzothieno-Fused BOPHY Dyes as Triplet Photosensitizers with Long-Lived Triplet Excited States.

The synthesis of a series of photostable [b]-benzothieno-fused BOPHY derivatives is reported via one-pot condensation of formylated isoindoles or formylindoles with hydrazine and subsequent boron complexation. These dyes show strong absorption in the deep red region and acceptable fluorescence quantum yields (∼30%). The two fused benzothiophene moieties are slightly deviated from the BOPHY core (with dihedral angles of 6.1 and 10.2°). This slightly twisted conformation brings an enhanced spin-orbit coupling and a reduced energy band gap between singlet and triplet states. The enhanced intersystem cross process endows these series of dyes with a good singlet oxygen quantum yield (up to 63%), a high triplet-state quantum yield (up to 78%), and a long lifetime value (up to 127 μs). Density functional theory calculations indicate that the transition from S1 to T2 states is crucial for triplet-state formation, highlighting their high efficiency in intersystem crossing. The calculated triplet electron spin surface reveals a widespread distribution of triplet states across the conjugated molecular structure, which enhances the Dexter mechanism for triplet energy transfer in these BOPHY photosensitizers. These findings are helpful for thorough understanding of the fundamental ISC process and developing triplet photosensitizers.

[2+2] and [2+1] Cycloaddition of myrcene for synthesis of highly strained bio-fuels with high density and high impulse

Developing bio-fuels provides a sustainable strategy to reduce the dependence on finite fossil fuels. But biomass-based fuel molecules usually lack strained structure, resulting in undesirable density and impulse for aerospace applications. Herein, the highly strained bio-fuels are synthesized from myrcene by photoinduced [2+2] cycloaddition and hydrogenation/cyclopropanation reactions. The triplet energy transfer mechanism is revealed through theoretical calculations, triplet quenching experiments and phosphorescent measurement. The reaction conditions of photocycloaddition reaction are optimized, including the photosensitizer type and amount, solvent effect, substrate concentration, reaction temperature and light intensity. Under the optimal conditions, the yield of target photocycloaddition products reaches ca. 82.61%, which are then hydrogenated and cyclopropanized to two kinds of bio-fuels, namely PC@HG and PC@CP, respectively, which have high density of 0.836 and 0.886 g·mL-1, high impulse of 326.71 and 329.42 s, superior cryogenic properties, and good combustion properties. This work provides a feasible pathway for the preparation of highly strained bio-fuels with high density and high impulse.

Regulation of Sensitized Phosphorescence in Two-Dimensional Lead Bromine Perovskites by Tuning Excited-State Interactions.

Excited-state interactions within the organic layer play a critical role in sensitized phosphorescence of two-dimensional (2D) perovskites. Herein, we regulate excited-state interactions utilizing isomeric organic ligands 1-naphthylmethylamine (1-NMA) and 1-(2-naphthyl)-methanamine (2-NMA). Transient absorption and first-principles calculations are employed to elucidate the mechanisms of triplet energy transfer (TET) and triplet excimer formation. The results indicate that wave function hybridization and tunneling effect at the inorganic/organic interface contribute to rapid (∼20 ps) and highly efficient (>98%) TET, with the triplet excimer being generated in (1-NMA)2PbBr4 at picosecond time-scale. However, triplet excimer is barely observed in (2-NMA)2PbBr4 due to varying ligand stacking modes. Despite rapid TET, the efficiency of sensitized phosphorescence is low (<0.5%), which is ascribed to pronounced nonradiative decay. By mixing isomeric ligands and optimizing respective ratio, a maximum phosphorescence enhancement of 7.6 folds is achieved. This work provides a detailed mechanistic understanding of triplet excimer sensitization and regulation of sensitized phosphorescence.

Photochemical Mechanism of Co-C Bond Activation via Triplet Energy Transfer in Ethyl(aqua)cobaloxime.

The photochemical decomposition of ethyl(aqua)cobaloxime, [EtCoIII(dmgH)2H2O], a vitamin B12 derivative model complex, was investigated to understand the mechanism of the Co-CEt bond scission induced by light. Upon irradiation of [EtCoIII(dmgH)2H2O], the Co-CEt bond undergoes homolytic scission, resulting in Et/Co(II) radical pair (RP) formation in a similar fashion observed in alkylcobalamins. The [EtCoIII(dmgH)2H2O] complex acts as a potent quencher of a wide variety of excited states in the presence of organic molecules such as benzophenone. It has been proposed that the reaction mechanism involves Dexter energy transfer, resulting in the bond dissociation process. Two issues associated with the proposed mechanism have been investigated, namely, (i) how the energy transfer occurs from benzophenone to cobaloxime and (ii) how the Co-CEt bond is activated and cleaved. Both TD-DFT and CASSCF/NEVPT2 methods have been applied to show the feasibility of the energy transfer reaction via the triplet pathway from photocatalyst to substrate.

Triplet Energy Transfer (EnT)-Promoted 1,3-Dipolar Cycloaddition Reactions of N-(Trimethylsilyl)methylphthalimide with Electron-Deficient Alkynes and Alkenes.

Triplet energy transfer (EnT)-promoted photochemical pathways, arisen by visible light and its photosensitizers, have gained significant attention as a complementary strategy for initiating organic transformations in photochemical reactions that are unlikely to occur through a single electron transfer (SET) process. In the present study, we investigated the triplet EnT-promoted 1,3-dipolar cycloaddition reactions of N-(trimethylsilyl)methylphthalimide with electron-deficient alkynyl and alkenyl dipolarophiles. The triplet excited state of N-(trimethylsilyl)methylphthalimide, promoted by the triplet EnT from thioxanthone (TXA) photosensitizer, underwent sequential intramolecular SET and carbon-to-oxygen migration of the silyl group to form azomethine ylide. This generated ylide cycloadded to alkynes or alkenes to regioselectively and stereospecifically produce a nitrogen-containing benzopyrrolizidine scaffold with multiple stereogenic centers. Crucially, the stereoselectivity of these cycloaddition reactions (i.e., endo versus exo addition) was influenced by the nature of the dipolarophiles.

Efficient photosensitized luminescence from Eu3+ in inert nanocrystals via ligand coordination

Abstract Luminescent lanthanide ions incorporated in sodium yttrium fluoride nanocrystals are promising as new luminescent materials in optoelectronics and bioimaging since the nonradiative transition is significantly suppressed due to the absence of high-energy vibrational modes. To prepare optically and electrically active nanocrystals, we explored organic ligands that allow efficient triplet energy transfer to Eu3+ incorporated into nanocrystals, resulting in an efficient photosensitization effect in colloidal solutions and films. Further, we applied these emitting nanocrystals to light-emitting devices and observed the electroluminescence.