Dexter Energy Transfer Research Articles

Benzophenone as a cheap and effective photosensitizer for the photocatalytic synthesis of dimethyl cubane-1,4-dicarboxylate.

The key intramolecular [2 + 2] photochemical cycloaddition step in the synthesis of dimethyl cubane-1,4-dicarboxylate is performed with substoichiometric amounts of the photosensitizer benzophenone. The reaction proceeds via a Dexter energy transfer process between the triplet excited state benzophenone and a well-known cubane precursor diene. The use of the cheap and widely available benzophenone as the photosensitizer enables lower energy light to be used than the traditional photochemical process.

High Efficiency and Long Lifetime Red Hyperfluorescence Organic Light Emitting Diodes through Dexter Energy Transfer Suppression

High Efficiency and Long Lifetime Red Hyperfluorescence Organic Light Emitting Diodes through Dexter Energy Transfer Suppression

Host-guest doping induced excited state energy transfer for efficient room temperature phosphorescence emission

The 1,8-naphthalimide derivatives as the guest and the benzophenone (BP) analogues bis(4-chlorophenyl)methanone (BP2C) and bis(4-fluorophenyl)methanone (BP2F) benzophenone derivatives as the host, we constructed a series of novel doping systems with fluorescence and room temperature phosphorescence (RTP) dual emission. The steady-state spectroscopy, ultrafast spectroscopy techniques, and theoretical calculations indicate that Förster resonance energy transfer (FRET) between singlet states between host and guest components enables energy redistribution in doped systems. At the same time, the Dexter energy transfer (DET) between the triplet states realizes the obvious absorption of the excited triplet state of the guest, resulting in the long-lived room temperature phosphorescence of the doped system. Doping materials have unlimited potential for information storage and anti-counterfeiting by exploiting the properties of photo activation.

Study on charge dynamics and recombination process via transient electroluminescence analysis in blue fluorescence organic light-emitting diodes

Fluorescent organic light-emitting diodes (FOLEDs) exhibit substantially different efficiency-lifetime characteristics depending on dopant materials even in the same host material. Thus, obviously charge and exciton dynamics and recombination process may vary depending on the dopants. However, an accurate understanding of charge and exciton dynamics with dopants in FOLEDS is lacking so far. Herin, triplet–triplet-fusion-based FOLEDs with two blue dopants, 2,5,8,11-tetra-tert-butylperylene (TBPe) and 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de] anthracene (t-DABNA) were investigated via transient electroluminescence (TrEL). Interestingly, the TrEL of the blue FOLEDs elucidated different charge profiles and recombination processes within the emission layers. The TrEL spikes after pulse-off and the characteristic times of EL intensity after pulse-on revealed the accumulated charge profile concerning the charge balance. In temperature-dependent TrEL, the delayed fluorescence, exciton decay time, and EL spikes after pulse-on reflected the emission mechanisms as well. The results showed that the electrical properties and the device performances of blue FOLEDs can be significantly impacted by the alignment of the energy levels of hosts and dopants, even with a low doping concentration. Furthermore, depending on the charge trap conditions, it was found that efficiency roll-off can be attributed to Dexter energy transfer from host to dopant and singlet–triplet annihilation by direct recombination on dopant molecules.

Sensitized 1-Acyl-7-nitroindolines with Enhanced Two-Photon Cross Sections for Release of Neurotransmitters.

Precise photochemical control, using two-photon excitation (2PE), of the timing and location of activation of glutamate is useful for studying the molecular and cellular physiology of the brain. Antenna-based light harvesting strategies represent a general method to increase the sensitivity to 2PE of otherwise insensitive photoremovable protecting groups (PPGs). This was applied to the most commonly used form of "caged" glutamate, MNI-Glu. Computational investigation showed that a four- or six-carbon linker attached between the 4-position of thioxanthone (THX) and the 4-position of the 5-methyl derivative of MNI-Glu (MMNI-Glu) would position the antenna and PPG close to one another to enable Dexter energy transfer. Nine THX-MMNI-Glu conjugates were prepared and their photochemical properties determined. Installation of the THX antenna resulted in a red shift of the absorption (λmax = 385-405 nm) along with increased quantum yield compared to the parent compound MNI-Glu (λmax = 347 nm). The THX-MMNI-Glu conjugate with a four-carbon linker and attachment to the 4-position of THX underwent photolysis via 1PE at 405 and 430 nm and via 2PE at 770 and 860 nm, yielding glutamate. The two-photon uncaging action cross section (δu) was 0.11 and 0.29 GM at 770 and 860, respectively, which was greater than for MNI-Glu (0.06 and 0.072 GM at 720 and 770 nm, respectively). The THX sensitizer harvested the light via 2PE and transferred its resulting triplet energy to MMNI-Glu. Release of glutamate through 2PE at 860 nm from the compound (100 μM) activated iGluSnFR, a genetically encoded, fluorescent glutamate sensor, on the surface of cells in culture, portending its usefulness in studies of neurophysiology in acute brain slice.

Designing three digital logic circuits based on two-component molecular systems of a combination of BSA and N, N′-bis(salicylidene) - ethylenediamine

A compound generally has only a single maximum emission wavelength. Therefore, it is relatively difficult to construct a dual-output molecular logic circuit. Herein, a novel fluorescent probe is designed by combining BSA and N, N′-bis(salicylidene)-ethylenediamine. The fluorescence intensity of the probe significantly fluorescence responses at 350 nm or 440 nm changed when stimulated with Zn2+, Fe2+, Cu2+, and EDTAH2Na2. Consequently, three different functional dual-output digit logic circuits are successfully designed in an aqueous solution. This combination is versatile with an additional advantage of water-solubility. Simultaneously, this combination provides a good reference model in exploring Dexter energy transfer in fluorescent experiments.

Achieving Efficient Solution‐Processed Blue Narrowband Emitting OLEDs with Small Efficiency Roll‐Off by Using a Bulky TADF Sensitizer with High Reverse Intersystem Crossing Rate

AbstractSolution‐processed organic light‐emitting diodes (OLEDs) based on multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters exhibit high color purity for next‐generation ultrahigh‐definition display. However, they suffer from low efficiency and large efficiency roll‐off due to slow triplet exciton upconversion of MR‐TADF emitters, resulting in serious triplet exciton quenching. Here, efficient solution‐processed blue MR‐TADF OLEDs featured with small efficiency roll‐off are developed by using a new bulky TADF sensitizer consisting of five di‐tert‐butylcarbazoles and one triazine with high reverse intersystem crossing rate of 2.0 × 107 s−1, which can rapidly convert triplet excitons to singlet ones to avoid exciton quenching. The Dexter energy transfer from the sensitizer to the MR‐TADF emitter is blocked by using tertiary butyl groups as the bulky unit in the sensitizer to increase the intermolecular distance for ensuring fast upconversion of triplet excitons on the sensitizer. And then the singlet excitons on sensitizer transfer to the emitter through long‐range Förster resonance energy transfer for narrowband emission. As a result, a maximum external quantum efficiency of 23.9% is achieved for the sensitized devices, slightly declining to 21.5% at a practical luminance of 1000 cd m−2. To the best of the authors’ knowledge, this is the best result for solution‐processed blue MR‐TADF OLEDs.

Regioselective Plasmon-Driven Decarboxylation of Mercaptobenzoic Acids Triggered by Distinct Reactive Oxygen Species

The non-radiative decay of surface plasmon resonance (SPR) in plasmonic metal nanoparticles (NPs) opens up unique hot-carrier-driven chemical transformation mechanisms. Here, the hot-carrier generation of reactive oxygen species was demonstrated to trigger the regioselective plasmon-driven decarboxylation of mercaptobenzoic acid (MBA) isomers over Ag (AgNPs) and Au nanoparticles (AuNPs). Controlled catalytic experiments indicated that the catalytic C–C bond cleavage over AgNPs and AuNPs is primarily initiated by photogenerated singlet oxygen (1O2) and hydroxyl radical (•OH), respectively. Energetic hot electrons on AgNPs can successfully generate 1O2 from 3O2 via Dexter energy transfer, while hot holes generated under the Fermi level of AuNPs have sufficient energy to oxidize OH– and promote the formation of reactive •OH. The catalytic activity trend was evaluated considering the known ortho-substituent effect. The data discussed herein shed light on how the intrinsic differences in electronic energy levels and metal–molecule interactions precisely tune the regioselectivity of plasmon-driven transformations and may guide the rational design of plasmonic catalysts for distinct desired reactions.

Sensitized triplet–triplet annihilation based photon upconversion in full organic and hybrid multicomponent systems

In the last 15 years, the attention dedicated to organic conjugated systems experienced outstanding growth because of the renewed interest in mechanisms involving triplet states such as singlet fission, thermally activated delayed fluorescence, and intersystem crossing enhanced phosphorescence. Photon upconversion via sensitized triplet–triplet annihilation (sTTA) enables the conversion of low-energy photons into high-energy ones, and it has been proposed in multicomponent systems as an efficient managing strategy of non-coherent photons. This mechanism exploits the annihilation of two optically dark triplet states of emitter moieties to produce high-energy photons. The annihilating triplets are sensitized through Dexter energy transfer by a light-harvester, typically a conjugated molecule or a nanocrystal, so sTTA upconversion is usually performed in bi-component systems. The high yield observed at low excitation intensities stimulated thriving research in the field, leading to the development of a large family of fully organic and hybrid sTTA multicomponent upconverters. Here, we compare the evolution of these two families of systems with respect to the sTTA upconversion main figures of merit, highlighting the strengths and weaknesses of both approaches, according to the results reported in the literature. The data presented are also discussed in the perspective of future developments in the field, pointing out the challenges that are still to be faced for the technological use of the sTTA upconversion process.

Energy Transfer Induced by TADF Polymer Enables the Recycling of Excitons in Perovskite Solar Cells

AbstractFormamidinium lead triiodide (FAPbI3) has been demonstrated as the most efficient perovskite system to date, due to its excellent thermal stability and an ideal bandgap approaching the Shockley‐Queisser limit. Whereas, there are intrinsic quantum confinement effects in FAPbI3, which lead to unwanted non‐radiative recombination. Additionally, the black α‐phase of FAPbI3 is unstable under room temperature due to the significant residual tensile stress in the film. To simultaneously address the above issues, a thermally‐activated delayed fluorescence polymer P1 is designed in the study to modify the FAPbI3 film. Owing to the spectral overlap between the photoluminescence of P1 and absorption of the above‐bandgap quantum wells of FAPbI3, the Förster energy transfer occurs at the P1/FAPbI3 interface, which further triggers the Dexter energy transfer within FAPbI3. The exciton “recycling” can thus be realized, which reduces the non‐radiative recombination losses in perovskite solar cells (PSCs). Moreover, P1 is found to introduce compressive stress into FAPbI3, which relieves the tensile stress in perovskite. Consequently, the PSCs with P1 treatment achieve an outstanding power conversion efficiency (PCE) of 23.51%. Moreover, with the alleviation of stress in the perovskite film, flexible PSCs (f‐PSCs) also deliver a high PCE of 21.40%.

Synthesis and Photophysical Studies of Copper(I) CAAC Half-Sandwich Complexes as a Highly Modifiable Class of Emitters.

Cyclopentadienyls are well-known strong donor ligands and have been successfully employed in catalysis as they tolerate a variety of substituents to adjust their steric and electronic properties. Although such highly modifiable ligands are of great interest for luminescence and photocatalytic applications, studies of CpR-containing photoactive transition-metal complexes are quite rare. In this work, we present a structural, electrochemical, and first elaborated photophysical investigation of a series of copper(I) half-sandwich complexes bearing cyclic alkyl(amino)carbenes (CAACs) as chromophore ligands and compare them with [Cu(Cp)(IDipp)] and [Cu(Cp*)(IDipp)] bearing a traditional N-heterocyclic carbene. Furthermore, we present the first molecular structure derived from single-crystal X-ray diffraction of a copper(I) indenyl complex, which can be described as an η2 (σ, π)-coordination. The CuI half-sandwich complexes show blue-green to orange phosphorescence with a photoluminescence quantum yield of up to 59% and radiative rate constants kr of up to 4 × 104 s-1 in the solid state, depending on the substitution pattern of the CpR ligand. Our TD/DFT calculations suggest that the emitting excited states are of 3MLCT/LLCT character. We determined the excited-state lifetime of the CuI half-sandwich complexes in solution to be as long as 600 ns, which in combination with the large π-surface of the CpR ligands allows for Dexter energy transfer for photocatalytic applications. In addition, the chiroptical properties of chiral [Cu(Cp/Cp*)(CAACMenthone)] were studied and compared to [CuCl(CAACMenthone)], of which we demonstrate that its circular polarized luminescence is the result of excimer formation and not, as previously reported, attributed to the monomeric C1-symmetric structure.

High‐Performance Blue Electroluminescence Devices Based on Linear Gold(I) Complexes as Ultrafast Triplet Exciton Harvesters

AbstractAchieving large external quantum efficiencies, narrow bandwidths, and a long operational lifetime at high brightness remains the largest hurdle to developing organic blue‐emitting devices. Here, a material strategy is demonstrated that can meet these conditions. The strategy is based on linear heteroleptic Au(I) complex exciton harvesters and multiresonance thermally activated delayed fluorescence (MR‐TADF) emitters. The organic electroluminescence devices produce blue emission with Commission Internationale de l'Eclairage chromaticity coordinates of (0.108, 0.160), a narrow full‐width at half‐maximum value of 20 nm, and a maximum external quantum efficiency (EQE) as high as 30.2%. Notably, the EQE value remains 22.2% at 2000 cd m−2, whereas conventional control devices with an organic exciton harvester suffer from huge roll‐offs in quantum efficiency. An additional benefit of the device is a one‐order‐of‐magnitude improvement in its operational lifetime compared with that of the control device. Finally, the investigations reveal that the improvements are attributable to the unique ability of the Au(I) complexes for ultrafast triplet exciton harvest. In addition, the Au(I) complexes can facilitate Förster energy transfer to the MR‐TADF emitter, with effective suppression of hazardous triplet–triplet Dexter energy transfer. It is believed that the research is helpful in commercializing high‐efficiency and stable blue electroluminescence devices.

Small molecule photocatalysis enables drug target identification via energy transfer

Over half of new therapeutic approaches fail in clinical trials due to a lack of target validation. As such, the development of new methods to improve and accelerate the identification of cellular targets, broadly known as target ID, remains a fundamental goal in drug discovery. While advances in sequencing and mass spectrometry technologies have revolutionized drug target ID in recent decades, the corresponding chemical-based approaches have not changed in over 50 y. Consigned to outdated stoichiometric activation modes, modern target ID campaigns are regularly confounded by poor signal-to-noise resulting from limited receptor occupancy and low crosslinking yields, especially when targeting low abundance membrane proteins or multiple protein target engagement. Here, we describe a broadly general platform for photocatalytic small molecule target ID, which is founded upon the catalytic amplification of target-tag crosslinking through the continuous generation of high-energy carbene intermediates via visible light-mediated Dexter energy transfer. By decoupling the reactive warhead tag from the small molecule ligand, catalytic signal amplification results in unprecedented levels of target enrichment, enabling the quantitative target and off target ID of several drugs including (+)-JQ1, paclitaxel (Taxol), dasatinib (Sprycel), as well as two G-protein-coupled receptors-ADORA2A and GPR40.

Efficient Solution‐Processed Red Fluorescent OLEDs Using Diluted Exciplex Host to Reduce Non‐Radiative Loss of Triplet Excitons

AbstractHigh‐performance red fluorescent organic light‐emitting diodes (OLEDs) are fabricated via a diluted exciplex host strategy to suppress non‐radiative triplet exciton loss in the exciplex sensitized fluorescent emitter system. The solution‐processed red fluorescent OLEDs based on the diluted TCTA:PO‐T2T exciplex host demonstrate higher external quantum efficiency (EQE) than the theoretical 5% limit for traditional fluorescent OLEDs. In the TCTA:PO‐T2T exciplex sensitized fluorescent emitter system, the excess content of TCTA is employed relative to PO‐T2T to manipulate the decay process of triplet excitons. A part of TCTA adjacent to PO‐T2T involves forming the exciplex pair that efficiently converts triplet excitons to singlet excitons via reverse intersystem crossing (RISC), while the other TCTA donors act as the host for the exciplex sensitizer and fluorescent emitter, which inhibits both concentration quenching of the exciplex sensitizer and short‐range dexter energy transfer from the exciplex sensitizer to the fluorescent emitter DCJTB without affecting ISC, RISC, and long‐range Föster energy transfer rate significantly. With this strategy, the formed triplet excitons can be converted to singlet excitons with reduced loss contributing to efficient fluorescent emission under electric excitation. The solution‐processed red fluorescent OLEDs achieve an EQE of 8.1%, much higher than 3.5% of the conventional exciplex sensitized OLEDs.

Thermally Activated Delayed Fluorescence Sensitizers As Organic and Green Alternatives in Energy-Transfer Photocatalysis

Photocatalysis has captured the imagination of synthetic chemists and is poised to become a staple of the fine chemical industry. Over the past decade, the subfield of energy-transfer (EnT) catalysis has expanded dramatically, harnessing the excited states of a photosensitizer to unlock a variety of redox-neutral, radical-based reactivities in a mild and selective fashion. However, many of the developments in this discipline rely on precious rare earth metals such as iridium. This perspective will highlight the rise of thermally activated delayed fluorescence (TADF) materials as metal-free alternatives in EnT photocatalysis for organic transformations. Emphasis will be placed on the recent progress of cycloadditions, E/Z isomerization of olefins, and other radical-initiated processes; all mediated by the mechanism of Dexter energy transfer. The tunable excited-state energetics and dynamics of TADF materials allow them to effectively compete with iridium-based sensitizers, indicating their promise as green alternatives in organocatalysis.

Superbly long lifetime over 13,000 h for multiple energy transfer channels in deep blue phosphorescence organic light-emitting diodes with Ir complex under CIEy of 0.17

Despite over two decades of relentless endeavor, the industrial application of blue phosphorescent organic light-emitting diodes (PhOLEDs) has not been realized due to extremely short lifetime. The degradation of PhOLEDs is generally accelerated at high current levels since high triplet energy with long exciton lifetime are mostly concentrated on host molecules and transferred to dopant via slow Dexter energy transfer (DET) processes rather than fast Förster resonance energy transfer (FRET) processes. Herein, we propose a novel device architecture that creates multiple energy transfer channels by employing an Ir-complex intermediate energy carrier (IEC). Unlike exciplex or electroplex, no excitons were generated between the host and the IEC even though the IEC also behaves as a p-type host. The most crucial role of the IEC is to diversify the energy transfer channels. By introducing the IEC in deep blue PhOLEDs, both FRET and DET channels were additionally created between the IEC and the host, and the IEC and the dopant. Consequently, an unprecedentedly long half luminance lifetime of 13,830 h at an initial luminance of 100 cd/m2 was obtained with a high efficiency of 14.4% and CIEy = 0.17. To our best knowledge, the lifetime in our report is the longest with a deep blue phosphorescent Ir complex.

Blocking the Energy Loss of Dexter Energy Transfer in Hyperfluorescence OLEDs Via One‐Step Phenyl‐Fluorene Substitution of TADF Assistant Host

AbstractGenerally, the charge transfer character of thermally activated delayed fluorescence (TADF) materials results in a long excitonic lifetime and broad‐band emission. With the combination of unity exciton utilization of TADF material and high radiative rate and narrow‐band emission of conventional fluorescence (CF) dopant, hyperfluorescence organic light‐emitting diodes (HF‐OLEDs) attract extensive attention in industry and academia recently. Till now, Dexter energy transfer (DET) from the triplet state of TADF assistant host to the dark triplet state of CF guest is the top‐drawer energy loss issue root in HF‐OLEDs. Herein, the energy loss of DET is blocked through one‐step substitution of TADF assistant host by electronically inert phenyl‐fluorene terminal for the first time. The blocking effect on DET process in HF‐OLEDs is investigated by means of photophysical characterization, theoretical calculation, device fabrication, and Monte Carlo simulation. The maximum external quantum efficiency of 18.1% with Commission Internationale de L'Eclairage coordinates of (0.61, 0.38) is achieved, which is on par with the state‐of‐the‐art efficiency for red HF‐OLEDs. This work presents a feasible design strategy for TADF assistant host aimed at achieving highly efficient HF‐OLEDs with narrow‐band emission.

Observation of up conversion/ down conversion luminescence and structural analysis of La2Zr2O7: Pr3+ nano phosphors

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La2Zr2O7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV–Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La2Zr2O7:Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications.

Luminescence properties and energy transfer of Ce3+/Eu3+ doped GSBA glass

Through the method of conventional high-temperature melting, Ce3+/Eu3+doped GeO2-SiO2-BaO-Al2O3 (GSBA) glasses were fabricated. Photoluminescence spectrum, Fourier transform infrared spectroscopy, absorption spectrum, fluorescence attenuation time and CIE color coordinates were tested to investigate the optical properties and structure of glass. Using the formula of Dexter's energy transfer, the energy transfer from Ce3+ to Eu3+ was studied. The band gap as well as spacing between rare earth ion were obtained by theoretical calculation. The results show that the optimal cerium ion concentration of the Ce3+ doped and Ce3+/Eu3+ co-doped GSBA glass was consistent, which is 0.3 mol%. For the samples only doped with Ce3+, there has no significant changes of glass structure with increasing Ce3+ concentration, and multiple ligands of [GeO4], [GeO6], [SiO4], [SiO4]&[GeO4], [AlO4] and [AlO6] co-existed in glass structure. It is proved that there is energy transfer from Ce3+ to Eu3+ and the form of energy transmission is electric quadrupole-quadrupole transfer. What's noteworthy is that in Ce3+/Eu3+ double-doped glass, the prepared glass material can emit white light through changing the doped concentration of Eu3+ ion, and color temperature is all below 3300 K, which proves the application potential of Ce3+/Eu3+ co-doped germanosilicate glass in the field of warm white LED.

Mechanistic insights into photochemical nickel-catalyzed cross-couplings enabled by energy transfer

Various methods that use a photocatalyst for electron transfer between an organic substrate and a transition metal catalyst have been established. While triplet sensitization of organic substrates via energy transfer from photocatalysts has been demonstrated, the sensitization of transition metal catalysts is still in its infancy. Here, we describe the selective alkylation of C(sp3)–H bonds via triplet sensitization of nickel catalytic intermediates with a thorough elucidation of its reaction mechanism. Exergonic Dexter energy transfer from an iridium photosensitizer promotes the nickel catalyst to the triplet state, thus enabling C–H functionalization via the release of bromine radical. Computational studies and transient absorption experiments support that the reaction proceeds via the formation of triplet states of the organometallic nickel catalyst by energy transfer.