Triplet-triplet annihilation upconversion materials as electrophoretic inks

Luminescent materials that can be reversibly switched by electric field stimulation are attractive since the potential application for optoelectronic devices.Here we report a triplet-triplet annihilation upconversion(TTA-UC)system with electrophoretic response which is developed as the electrophoretic ink.The TTA-UC system consists of an ionic derivative of 9,10-diphenyl anthracene(DPA)as the annihilator and Pt(II)octaethylporphyrin(PtOEP)as the sensitizer.Upon applying an electric field,migration and enrichment of positively charged DPA derivatives towards the cathode results in a 20%enhancement of TTA-UC.A quasi-solid film for electrically writing is made using the electrophoretic TTA system as the ink and a platinum electrode as a pen.The prototype of TTA-UC ink demonstrates unique luminescence functions upon electrically writing and erasing,providing a promising strategy to develop electronic devices for display,information storage and encryption.

Study on the energy level limitations of triplet-triplet annihilation upconversion with anthracene-isomerized dimers as annihilators

The enhancement in the efficiency of triplet-triplet annihilation upconversion(TTA-UC)is mainly determined by the triplet energy transfer(TET)and triplet-triplet annihilation(TTA)between the sensitizers and annihilators.The TET process works efficiently by adjusting the concentration ratio of the sensitizers and annihilators.The efficiency of TTA is determined by the properties of the annihilator.Because TTA is a Dexter-type energy transfer and is affected by the diffusion rate,the energy levels of the excited states and the molecular size are both crucial in TTA.In this study,four isomerized dimers of 9,10-diphenlanthracene(DPA)and anthracene(An)were designed and prepared as annihilators for TTA-UC.The singlet and triplet energy levels could be adjusted by altering the connection position while maintaining the molecular weight and size.When PtOEP was used as the sensitizer,the maximum upconversion efficiency of 9-[4-(9-anthracenyl)phenyl]-10-phenylanthracene(9DPA-9An)was~11.18%.This is four times higher than that of 9,10-diphenyl-2,9-bianthracene(2DPA-9An,2.63%).The calculation of the energies of T_(1)and the higher triplet state(T_(3),because E(T_(2))is similar to the E(T)of these dimers)for these dimers has provided insights into the underlying reasons.These indicated that the energy gap value of 2×E(T_(1))-E(T_(3))is the determining factor for TTA efficiency.This work may provide a better understanding of the excited-state energy levels,which is crucial for designing novel annihilators to enhance the TTA-UCefficiency.

Recent Advances in Triplet-Triplet Annihilation Upconversion for Bioimaging and Biosensing

Photon upconversion is an anti-Stokes process that converts low-energy photons into high-energy photons.The use of upconversion luminescence can avoid the autofluorescence of biological tissue and realize background-free bioimaging with a high signal-to-noise ratio at a low power density.In addition,the excitation of red or near-infrared light facilitates the reduction of photodamage in biological tissues and subsequent bioimaging of deep tissue features in vivo.Meanwhile,upconversion emission-mediated bio sensing offers both high sensitivity and low detection limits for quantitative analysis of the target substances in complicated biological samples.Due to its high upconversion quantum yield,low excitation power density,and tunable absorption and emission wavelengths,triplet-triplet annihilation upconversion(TTA-UC)has garnered considerable interest for bioimaging and biosensing.This review will introduce the fundamental concepts of TTA-UC,the factors that influence TTA-UC materials,and the methodologies for preparing TTA-UC materials.The important progress of TTA-UC in bioimaging and bio sensing in recent years will also be discussed in detail in vitro and in vivo.Furthermore,the current challenges of TTA-UC in bioimaging and biosensing will be discussed,along with potential solutions.

A Fluorescein Derivative Chemosensor Combined with Triplet-Triplet Annihilation Upconversion System for Ratiometric Sensing of Cysteine

A derivative of fluorescein,fluorescein O,O-diacrylate(FODA),was utilized in a triplet-triplet annihilation upconversion(TTA-UC)system to develop a composite ratiometric chemosensor capable of detecting cysteine(Cys).FODA acted as both the probe for Cys and the energy acceptor for upconversion(UC)emission,thereby making UC a responsive signal to Cys.In addition,the phosphorescence signal of the sensitizer in the TTA-UC system remained constant and did not respond to Cys,making it an ideal internal reference signal for constructing a ratiometric sensor.Through this simple strategy,traditional fluorescent probes can be combined with TTA-UC system to establish a ratiometric sensing platform,which can be applied in more scenarios due to the longer wavelength excitation.

Efficient soluble deep blue electroluminescent dianthracenylphenylene emitters with CIE y(y≤0.08) based on triplet-triplet annihilation

It has been challenging to develop deep blue organic molecular fluorescent emitters with CIE y(y≤0.08)based on triplet-triplet annihilation(TTA). Here, we report facilely available dianthracenylphenylenebased emitters, which have a 3,5-di(4-t-butylphenyl)phenyl moiety at the one end and 4-cyanophenyl or 3-pyridyl at the other end, respectively. Both fluorophores show a high glass transition temperature of over 220℃ with a thermal decomposition temperature of over 430℃ at an initial weight loss of1%. The preliminary characterizations of the organic light-emitting diodes(OLEDs) that utilized these nondoped emitters provided high EQEs of 4.6%à5.9% with CIE coordinates(0.15, 0.07–0.08). The analysis of the EL transient decay revealed that TTA contributed to the observed performance. The results show that the new emitters are attractive as a potential TTA-based host to afford stable deep blue fluorescent OLEDs.

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

The novel triplet–triplet annihilation(TTA)upconversion(UC)field of rubrene(Rub)and dibenzotetraphenylperiflanthene(DBP)sensitized by bulk metal halide perovskite,integrated with copper-2,3,9,10,16,17,23,24-octafluorophthalocyanine(F_(8)CuPc)as cosensitizer,have been investigated in perovskite solar cells(PVSCs)to minimize sub-bandgap photon transmission loss.The firm hydrogen bonding interaction(F…H–N between F_(8)CuPc and MA+),cation-πinteraction(MA+with Rub),and the hydrophobic characteristic of additives enable F_(8)CuPc:Rub:DBP dually-sensitized p-i-n PVSCs based on MAPbI_(3)and Cs_(0.05)(FA_(0.83)MA_(0.17))_(0.95)Pb(Br_(0.17)I_(0.83))_(3)absorbers to attain champion efficiencies of 20.83%and 21.51%,respectively.Furthermore,due to the excellent photochemical and thermal stability of F_(8)CuPc,the corresponding PVSCs can maintain nearly 80%of the original efficiencies exposed to air with 50∼70%relative humidity over 1100 h and N_(2)at 85℃for 300 h.

Assembly-enhanced triplet-triplet annihilation upconversion in the aggregation formed by Schiff-base Pt(Ⅱ) complex grafting-permethyl-β-CD and 9,10-diphenylanthracence dimer

Water-soluble triplet sensitizer with permethyl-β-cyclodextrin(PMCD)grafting on a Schiff-base Pt(II)complex(Pt-2),in which PMCD unit serves as a host for binding the acceptors and the Schiff-base Pt(II)complex serves as a triplet sensitizer,was synthesized to investigate the effect of supramolecular complexation and assembly on the triplet-triplet annihilation upconversion emission in water.9,10-Diphenylanthracence(DPA)carboxylate(A-1)and its dimer(A-2)in which two DPA carboxylate were covalently linked with an alkyl chain were synthesized as triplet acceptors which also play a role of guest molecules for PMCD.A-1 and A-2 showed high affinity with PMCD,and A-2 can readily aggregate in water and form micron sized assemblies due to the hydrophobic effect andπ-πstacking of anthracene core in A-2.The efficiency of TTA-UC was demonstrated to be enhanced by a synergistic effect of host-guest complexation of Pt-2 with A-2 and the self-aggregation of the acceptor A-2,which facilitated the energy transfer and energy fusion among donor and acceptor.

Three-dimensional direct-writing via photopolymerization based on triplet-triplet annihilation

3D direct-writing via photopolymerization based on two-photon absorption(TPA) can achieve excellent out-of-plane resolution.The key to this technology is a quadratic intensity dependence in photoexciting the TPA photosensitizers. Triplet-triplet annihilation(TTA) also has similar nonlinear light-intensity dependence. As a result, TTA can also generate spatially confined excitation near the beam focus. Combining the photopolymerization reaction with the TTA system composed of palladium porphyrin and diphenylanthracene, 3D direct-writing micro-fabrication based on photopolymerization and the TTAwas realized.The out-of-plane resolution can reach 10 μm under continuous-wave laser excitation. TTA-based 3D direct-writing technology does not need an expensive femtosecond pulsed laser, showing the potential of a next-generation 3D printing technology.

三线态转换的蓝光电致发光材料研究进展

有机电致发光二极管(organic light-emitting diodes,OLEDs)经历了30年的发展,发展蓝色有机电致发光分子,特别是能够有效利用三线态激子的三线态-三线态湮灭(triplet-triplet annihilation,TTA)和杂化局域-电荷转移(hybrid locally and charge-transfer excited state,HLCT)分子,是当下的研究热点。对近5年具有代表性的蓝光TTA和HLCT电致发光材料进行了梳理,期望激发该领域的研究,加速实现高效、长寿命的蓝光OLED器件。

Amplified circularly polarized luminescence enabled by photon upconversion in spin-coating cellulose matrix

It is of great significance to construct organic circularly polarized luminescence systems(CPL) with large luminescence dissymmetry factors(g_(lum)) for practical applications. Here we report organic CPL systems constructed by merging triplet-triplet annihilation upconversion chromophores in cellulose matrices. The chirality of the matrix is transferred to the achiral chromophores of photon upconversion and then the multistep energy transfer processes of upconversion amplify g_(lum). The g_(lum)value of upconversion CPL in the left-handed ethyl cellulose and the right-handed(acetyl) ethyl cellulose are up to +0.1 and -0.15, respectively. The study provides a straightforward approach for constructing solid organic upconversion CPL materials with large g_(lum), which may expand the application potentials of organic chiroptical materials.

基于三线态-三线态湮灭的能量上转换

能量上转换近些年来引起了人们的广泛关注,具有许多方面的潜在应用,包括光伏技术、光合成、光催化和生物成像等。基于三线态-三线态湮灭(TTA)的能量上转换由于其具有激发光不需要是相干光,强度低,而且只要通过改变TTA过程中不同的敏化剂和受体,就能改变TTA上转换的激发光和发射光的波长等优点,有着广泛的应用前景。本文介绍了TTA上转换的机理,综述了TTA上转换近些年来的研究进展,总结了一些常用的敏化剂和受体,讨论了TTA上转换目前存在的问题及今后的发展方向。

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence(TADF) organic molecules feature with long-lived delayed fluorescence, because they can undergo not only efficient intersystem crossing(ISC), but also efficient reverse intersystem crossing(RISC) at room temperature. As a new type of luminescent molecules, they have exhibited successful applications in organic light emitting diodes(OLEDs). Aside from OLEDs, they are also found to have potential applications in time-resolved luminescence imaging based on long-lived fluorescence property. Meanwhile, due to their excited triplet characteristic originated from efficient ISC,they were found to be applied in triplet-triplet annihilation upconversion(TTA-UC), photodynamic therapy(PDT) and organic photocatalytic synthesis. This review briefly summarizes the characteristics and excellent photophysical properties of TADF organic compounds, then covers their applications to date aside from OLEDs based on their highly efficient ISC ability and RISC ability at room temperature.

Recent research progress for upconversion assisted dye-sensitized solar cells

Upconversion(UC)technology makes it possible to harvest infrared(IR)light from the sun and has increasingly been employed in recent years to improve the efficiency of solar cells.The progress in the area concerns both research on fundamental principles and processes of UC and technologies of device fabrication.Significant increase of important solar cell parameters,like short-circuit photocurrent density and open-circuit photovoltage as well as the total photon-to-current efficiency,has been accomplished.We here review the research published during the last few years in the area,in particular we consider the two most cherished techniques,namely the incorporation of upconverting nanophosphors directly into the photoanodes of the solar cells and the introduction of plasmonic metal nanoparticles co-existing with the UC particles.Other ways to achieve strong field enhancement,and the use of the non-linear nature of UC,is to apply microlenses,with or without assisting plasmonic excitation.Further enhanced UC action has been demonstrated by broad band and effective harvesting by organic IR antennas,with subsequent mediation by an intermediate nanoshell of the energy into the upconverting core.Codoping,nanohybrid and layer-by-layer technologies involving upconverting particles as well as the use of upconverting nanoparticles in hole-transport and electrolyte layers,tested in recent works,are also reviewed.While most of these technologies employ upconverting rare earth metals for sequential photon absorption,the main alternative technique,namely triplet-triplet annihilation UC using organic materials,is also reviewed.It is our belief that all these approaches will be further much researched in the near future,with potentially great impact on solar cell technology.

Multiple Resonance Thermally Activated Delayed Fluorescence Sensitizers Enable Green-toUltraviolet Photon Upconversion:Application in Photochemical Transformations

Efficient visible-to-ultraviolet(UV)triplet-triplet annihilation upconversion(TTA-UC)with large anti-Stokes shift is highly promising for solar-powered and indoor applications.Nonetheless,the excitationwavelengthis confined to the blue region(<450 nm),mainly due to large energy loss during triplet sensitization,resulting in reduced photon utilization efficiency in practical scenarios.Herein,a series of multiple resonance thermally activated delayed fluorescence(MR-TADF)compounds are developed as purely organic sensitizers for the purpose of energy-loss reduction,which also feature intense absorbance in the visible region,high intersystem crossing efficiencies,and long triplet lifetimes.By pairing the MR-TADF sensitizers with appropriate acceptors,green-to-UV TTA-UC systems were realized with an anti-Stokes shift up to 1.05 eV,upconversion quantum yield up to 8.6%,and threshold excitation intensity as low as 9.2 mW cm^(−2) in solution.The TTA-UC pairs were applied as internal or external sources of UV photons to trigger energy-demanding photopolymerization and photoligation reactions even under excitation of low-power-density green light-emitting diode light,revealing the broad utility of thesemolecular upconverters.This work unlocks the huge potential of MR-TADF-type sensitizers in upconversion applications.

Molecular core–shell structure design:Facilitating delayed fluorescence in aggregates toward highly efficient solution-processed OLEDs

Light has been sought and explored by human since ancient times.As the most important form of light,fluorescence is significant to applications in bioimaging and optoelectronic devices.However,fluorescence quenching problem constitutes a serious bottleneck in materials creation.Inspired from the core–shell structure in nature,we report an effective strategy to overcome this long-standing problem by utilizing a molecular core–shell structure.With an emissive core and multifunctional shell fragments,these compounds show aggregation-induced delayed fluorescence(AIDF)properties by restricting singlet oxygen(^(1)O_(2))generation and suppressing the triplet–triplet annihilation(TTA).Protected by the functional shell,the aggregation-induced emission luminogens(AIEgens)exhibit strong emission with high photoluminescent quantum yield and exciton utilization.Furthermore,because the shell materials can form exciplex with electron-transport materials,the fully solution-processed organic light-emitting diodes(OLEDs)based on these core–shell materials show low turnon voltages,excellent device performance with current efficiency of 61.4 cd A–1 and power efficiency of 42.8 lm W–1,which is a record-breaking efficiency based on all-solution processed organic multilayer systems among the AIE-OLEDs so far.This simple visualization strategy based on molecular core–shell structure provides a promising platform for AIEgens used in the fully wet-processed optoelectronic field.