有机发光材料中的三重激发态（英文）

有机发光材料有望广泛应用于新一代柔性光电子器件。由于自旋多重性,有机分子发光材料中单重激发态和三重激发态转换较慢,限制有机发光器件特别是电注入荧光器件的效率。我们介绍下近年来通过分子设计操控激发不同时间尺度三重态的动力学来突破这一限制的策略,通过控制激发单重态和激发三线态之间的电子耦合,利用热激子系间窜越、反向系间窜越、激发三重态稳定化等过程能够有效提高有机发光材料的发光效率。在此基础上实现的热活化延迟荧光、有机长余辉发光等在有机发光二极管、传感器、生物成像等领域有重要潜在应用价值。     

利用磁致发光曲线研究Rubrene器件中激子分裂和湮没过程

为了研究Rubrene分子中激发态的能量共振和分子间π-π共轭的特性对有机磁效应的影响, 本文制备了基于不同浓度和厚度的Rubrene有机发光器件, 并在不同温度下测量了器件的电致发光磁效应(magneto-electroluminescence, MEL). 实验发现, 发光层中Rubrene的厚度和浓度均可以对器件中的MEL产生较大的影响, 室温下MEL的高场值随Rubrene层厚度的增加而增加, 并在30 nm之后逐步趋于饱和; 随着Rubrene分子的浓度和测量温度的降低, MEL高场增加的幅度逐渐减小, 甚至在低温时出现高场下降. 通过对实验曲线进行数值拟合, 认为Rubrene分子之间形成的π-π共轭结构有助于双分子相互作用的发生, 单重态激子分裂、三重态激子之间的湮没和单-三重态极化子对的系间窜越三种过程在器件中相互竞争导致了所得MEL的变化. 本工作有助于加深对有机光电子器件内部机理的认识.     

树枝状热活化延迟荧光材料研究进展

树枝状发光材料是一类由中心核和外围树枝构成的具有三维空间结构的发光功能材料,既具有有机小分子发光材料明确的化学结构和确定的分子量,又具有高分子发光材料的良好溶液加工性能,是发展低成本、高效率有机电致发光器件的重要材料体系。具有热活化延迟荧光效应的树枝状发光材料能够通过反向系间窜越过程将三线态激子转变为单线态激子而发出荧光,其器件理论内量子效率可以达到100%,是开发设计高效树枝状发光材料的有效途径。近年来,在分子设计方面,树枝状热活化延迟荧光材料取得了重要进展,形成了种类丰富的材料体系,同时其器件性能得到了大幅提升。本文根据树枝状热活化延迟荧光材料的中心核进行分类,围绕其分子设计、光物理特性和器件性能,总结和评述了国内外研究者在该领域的主要研究进展,并分析了其未来发展所面临的机遇和挑战。     

过渡金属配合物TADF发光材料研究进展

高效率利用三重态激子发光是制备高性能有机发光二极管（OLED）的关键。除磷光过渡金属配合物外,具有热活化延迟荧光（TADF）特性的过渡金属配合物能够将三重态激子上转换为单重态激子,进而通过单重态激子辐射发光,为开发金属配合物发光材料提供了新的途径。然而,过去十年来OLED发光材料的研究主要聚焦在纯有机TADF体系上,过渡金属配合物TADF材料的研究投入相对偏少。但是,已有研究表明金属配合物能够利用金属的重原子效应促进反向系间窜越（RISC）过程,提升TADF发光效率并缩短TADF寿命,有利于制备高效率、低滚降的OLED。本文根据金属中心不同的d电子构型分类筛选了TADF金属配合物研究领域中代表性的材料体系,对其激发态属性、光物理和器件性能进行了概括和讨论。通过对不同类型的TADF金属配合物发光性能的归纳和比较,揭示了金属中心和配体结构对配合物发光性质的影响规律,对进一步开发高性能的金属配合物TADF材料,尤其是基于廉价金属元素的TADF配合物具有重要的指导意义。     

类富勒烯团簇发光性能的理论研究

热激活延迟荧光(TADF)作为一种特殊的分子荧光机制,对于提高发光效率有着重要意义.以C₆₀和C₇₀为代表的碳富勒烯具有高对称结构和离域π电子,被广泛证明具有显著的TADF效应;相比之下,其他类富勒烯团簇的光物理性质尚不清楚.本文利用含时密度泛函理论探索了一系列类富勒烯团簇的激发态性质,包括实验合成的具有不同尺寸的氮化硼笼型团簇B₁₂N₁₂, B₂₄N₂₄和B₃₆N₃₆,以及与B₁₂N₁₂结构相同、元素组成不同的B₁₂P₁₂, Al₁₂N₁₂和Ga₁₂N₁₂.计算结果表明,这些类富勒烯化合物团簇具有2.83—6.54 eV的能隙,主要吸收紫外光,荧光发射波长在可见光区间,包括红光、橙光、蓝光和紫光.它们的第一激发单重态和三重态的能量差较小(...     

掺杂型有机电致发光二极管的研究进展

有机电致发光具有结构简单、成本低、平面光源、节省能源等优点,其中掺杂型电致发光二极管因可以同时利用单重态和三重态的激子来发光和理论上能使器件内量子效率达到100%而倍受关注。从掺杂型电致发光二极管发光机理、主体材料、掺杂剂材料、白光器件几个方面阐述了该领域的研究进展。     

分子间相互作用对有机分子发光性质的影响

有机固态发光材料因其在显示器、激光和光通信等领域的应用前景而受到越来越多的关注. 与单分子相比,有机固态中存在各种弱分子间相互作用,这些相互作用有时会对激发态性质和能量耗散途径产生较大的影响,从而产生较强的荧光或磷光. 因此揭示有机固态发光的内在机制是非常必要的. 本综述通过总结从单分子到聚集态激发态的几何结构、电子结构、电子振动耦合和能量耗散动力学的变化,简要概括了分子间相互作用如何诱导有机固体产生强荧光、热激活延迟荧光和室温磷光. 本综述希望能帮助深入理解有机固体的激发态特性,从而为设计优秀的固态发光材料提供思路.     

有机电致发光器件的磷光发光研究

研制了一种以铕钇络合物（Eu0.1Cd0.9)(TTA)3(TPPO)2为发光材料的新型有机电致发光器件,观察到了三重态的磷光发光现象,分析表明此电致磷发光是Gd^3 对络合物配体电子自旋轨道强烈扰动引起的三重态发光。同时用积分球方法测定了该器件在不同温度下的光致发光和电致发光效率,结果表明此磷发光效地提高了器件的电致发光效率。     

溶剂化对有机给、受体分子热激活延迟荧光的影响及调控EI北大核心CSCD

具有热激活延迟荧光(Thermally activated delayed fluorescence,TADF)特性的有机给、受体(Donor-acceptor,D-A)分子体系通过反向系间窜越捕获三重态激子,可以将内量子效率的理论上限提高到100%,因而受到极大关注。通常,具有分子内电荷转移特性的D-A体系可以通过构建扭曲的分子构象来减小单、三重态之间的能差ΔES-T,以确保反向系间窜越快速发生。当分子被激发后,若激发态构象中D-A的二面角更接近90°时,ΔES-T会更小,延迟荧光也会增强。然而,快速的溶剂化过程常常会影响激发态构象、分子内电荷转移过程、延迟荧光发射,这使得研究TADF分子发光过程更富有挑战。本文综述了本课题组近期在溶剂化对D-A体系延迟荧光的影响及调控方面所取得的初步进展。结果显示,强极性溶剂会导致非辐射弛豫增加,不利于TADF发射;改变溶剂粘度会影响激发态构象弛豫,从而可以实现对TADF的增强或减弱的调控。这些结果有助于理解溶剂化效应与构象弛豫、TADF之间的关系,为TADF分子的设计与合成提供指导。     

OLED发光材料的理论计算与分子设计

数次有机发光二极管（OLED）器件效率的突破均源于有机电致发光新机制的发现和有机发光材料的创新。理论探究有机分子激发态的形成和衰变过程可以加深理解发光的微观机理,促进发光材料分子的研发。本文简要介绍了热振动关联函数（TVCF）的速率理论,及其在荧光、磷光和热激活延迟小分子材料中的应用。针对这三类小分子材料,我们揭示了其发光机理,建立了分子结构与性质之间的关系,提出了表征效率的描述符,并理论设计了优良的OLED发光分子。     

Room‐Temperature Phosphorescence in Metal‐Free Organic Materials

Purely organic materials with room‐temperature phosphorescence (RTP) have attracted a growing interest for their potential applications in biological imaging, digital encryption, optoelectronic devices, and so on. To date, many strategies have succeeded in designing efficient organic RTP materials by overcoming the spin‐forbidden transition between singlet and triplet states. However, the underlying mechanisms of RTP still remain ambiguous. Such spin prohibition in phosphorescence are clarified, herein, from the perspective of perturbation theory, helping to understand the intrinsic relationship among various phosphorescence parameters, like phosphorescence efficiency, lifetime, intersystem crossing rate, as well as radiative and nonradiative rates. Taking into consideration the recent progress in organic RTP materials, these factors are further illustrated by a selection of the most relevant molecules. In addition, some novel RTP phenomena are also reviewed, thus providing an excellent guideline to constructing efficient RTP materials.     

B-type delayed fluorescence of rubreneperoxide in solution.

B-type of delayed fluorescence was observed for the first time for rubreneperoxide. Rubreneperoxide molecules were excited in a two step process. In the first step an excited singlet S₁ is created, which undergoes intersystem crossing to T₁; then T-T absorption creates an excited triplet rubreneperoxide molecule, which returns to the first excited singlet level by intersystem crossing. The recreated first excited singlet of rubreneperoxide decays back to the ground state by emitting B-type of delayed fluorescence.     

High Resolution B-Type Delayed Fluorescence of Dibenzanthracene in PMMA

B-Type delayed fluorescence of 1,2,3,4-dibenzanthracene in PMMA was experimentally observed for the first time. Dibenzanthracene molecules were exerted in a two-step process. In the first step, an excited singlet S₁ is created, which undergoes intersystem crossing to T₁ then T-T absorption creates an excited triplet dibenzanthracene molecule, which returns to the first exerted singlet level by intersystem crossing. The recreated first excited singlet of dibenzanthracene decays back to the ground state by emitting this new type of delayed fluorescence.     

Photophysics ofβ-carotene and related compounds (review)

A review of data on the photophysics of carotenoids is presented. Results of investigations of spectroscopic, temporal, and energy parameters of excited S₁ and S₂ singlet states of β-carotene and related compounds are critically examined. These states give rise to extremely high probabilities (10¹¹–10¹³ sec⁻¹) of radiationless deactivation of the electronic excitation energy in carotenoids. Results of investigations of photophysical properties of triplet states of carotenoids are considered mainly from the standpoint of quenching of singlet oxygen and triplet states of organic molecules by carotenoids. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 5–19, January–February, 1997.     

Influence of solvent polarity and temperature on dual fluorescence of 10,10′-dibromo, 9,9′-bianthryl

Fluorescence of 10,10′-dibromo, 9,9′-bianthryl (DBrBA) in solvents of different polarities (n-hexane, dibutyl ether, tetrahydrofuran, and acetone) has been investigated as a function of temperature. Changing of the solvent and variation of temperature modifies the ratio of local (LE) and charge transfer (CT) fluorescence quantum yields. From the basic fluorescence data (quantum yields, lifetimes, ratio of CT to LE fluorescence quantum yields) the temperature-dependent equilibrium constants for the charge transfer process in the excited singlet state were calculated and discussed on the basis of the modern electron transfer theories. It has been found that the intersystem crossing in DBrBA in nonpolar n-hexane, leading to the population of the lowest triplet state, proceeds via the third triplet state. It has been confirmed by the fluorescence measurements and quantum mechanical calculations. Surprisingly, the experimentally obtained intersystem crossing rate constants are very weakly dependent on temperature. Thus, the electron transfer reaction leading to the population of the molecular triplet state is probably an adiabatic reaction with a rate constant controlled by the dielectric relaxation of the solvent.     

Probability estimate for intersystem crossings in naphthalene and acenaphthene in the presence of benzophenone

To a first approximation in perturbation theory, we have obtained expressions for the rate constants for intersystem crossings in acceptor molecules. We show that exchange interactions between the components of the donor-acceptor pair can change the probability of intersystem crossings for both radiative T → S₀ and nonradiative S₁ → T transitions. The theoretical conclusions are supported by the results of experimental studies. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 550–553, July–August, 2006.     

表观遗传修饰核酸碱基的超快激发态动力学研究

核酸碱基的表观遗传修饰是生命体实现表观遗传功能的重要组成部分，可以直接参与调控细胞分化、基因表达等重要的生理过程。然而，核酸碱基的光稳定性会受表观遗传修饰的影响，相应的碱基可能成为紫外线诱导皮肤癌产生的重要突变位点。因此，研究表观遗传修饰对核酸碱基的光物理与光化学性质的影响具有十分重要的意义。本文综述了近年来本课题组利用超快时间光谱技术结合高精度的量子化学理论计算对一系列表观遗传修饰的核酸碱基激发态动力学性质的研究。研究表明，表观遗传修饰对碱基激发态性质的影响主要分为三个方面：显著增长ππ^∗1态的寿命、引入分子内电荷转移态、有效促进单重态到三重态系间窜跃。     

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

Time-resolved EPR spectra are reported for porphyrin-quinone-quinone and porphyrin-porphyrin-quinone triads obtained after photoexcitation in the nematic and soft glass phase of liquid crystals. Spin-polarized EPR spectra were observed for the triplet states of the porphyrin created by spin-selective intersystem crossing (ISC) from the excited singlet state and those of the charge-separated radical pair states (RP) generated by electron transfer (ET) processes. The EPR polarization patterns of the RP are discussed in terms of the favored decay channel of the photoexcited singlet state of the porphyrin donor. The decay pathway may either be singlet ET to the quinone(s) followed by singlet/triplet mixing to yield RPs with triplet character or triplet ET after ISC from the porphyrin singlet to the triplet state, or a superposition of both pathways. It is demonstrated that the nature of the linking bridge between donor and acceptor, i.e., aliphatic cyclohexylene or aromatic phenylene, significantly influences the ET mechanism and thus the polarization patterns of the RP spectra. Using liquid crystals, information about the orientation of the guest molecules in the liquid crystal matrix with respect to the long axes of the liquid crystal molecules can be obtained. In the porphyrin-porphyrin-quinone triads the energy and ET processes strongly depend on the type of metallation of the porphyrins, specifically, whether the distal, the vicinal or both porphyrins bear a zinc atom.     

单线态分裂的超快光谱学研究

有机分子中的单线态分裂过程能将单个光激发的单线态激子转化成两个三线态激子. 借助此载流子倍增效应, 太阳能电池可以更有效地利用太阳光谱中的高能光子, 进而突破单结太阳能电池效率的理论极限. 因此, 单线态分裂备受关注. 本文回顾学术界对单线态分裂物理图像的认识以及争议, 结合课题组近年来的一些结果, 重点总结此领域中运用瞬态光谱学方法取得的实验进展, 讨论有关多激子中间暗态机理的不同观点, 并介绍单线态分裂材料的发展以及器件应用.