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Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states.

ABSTRACT: The harvesting of 'hot' triplet excitons through high-lying reverse intersystem crossing mechanism has emerged as a hot research issue in the field of organic light-emitting diodes. However, if high-lying reverse intersystem crossing materials lack the capability to convert 'cold' T₁ excitons into singlet ones, the actual maximum exciton utilization efficiency would generally deviate from 100%. Herein, through comparative studies on two naphthalimide-based compounds CzNI and TPANI, we revealed that the 'cold' T₁ excitons in high-lying reverse intersystem crossing materials can be utilized effectively through the triplet-triplet annihilation-mediated high-lying reverse intersystem crossing process if they possess certain triplet-triplet upconversion capability. Especially, quite effective triplet-triplet annihilation-mediated high-lying reverse intersystem crossing can be triggered by endowing the high-lying reverse intersystem crossing process with a ³ππ*→¹nπ* character. By taking advantage of the permanent orthogonal orbital transition effect of ³ππ*→¹nπ*, spin-orbit coupling matrix elements of ca. 10 cm^-1 can be acquired, and hence ultra-fast mediated high-lying reverse intersystem crossing process with rate constant over 10⁹ s^-1 can be realized.

SUBMITTER: Luo Y

PROVIDER: S-EPMC9653383 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature

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Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states.

Luo Yanju Y Zhang Kai K Ding Zhenming Z Chen Ping P Peng Xiaomei X Zhao Yihuan Y Chen Kuan K Li Chuan C Zheng Xujun X Huang Yan Y Pu Xuemei X Liu Yu Y Su Shi-Jian SJ Hou Xiandeng X Lu Zhiyun Z

Nature communications 20221112 1

The harvesting of 'hot' triplet excitons through high-lying reverse intersystem crossing mechanism has emerged as a hot research issue in the field of organic light-emitting diodes. However, if high-lying reverse intersystem crossing materials lack the capability to convert 'cold' T<sub>1</sub> excitons into singlet ones, the actual maximum exciton utilization efficiency would generally deviate from 100%. Herein, through comparative studies on two naphthalimide-based compounds CzNI and TPANI, we ...[more]

PMID: 36371489

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Project description:Owing to their exceptional photophysical properties and high photostability, perylene diimide (PDI) chromophores have found various applications as building blocks of materials for organic electronics. In many light-induced processes in PDI derivatives, chromophore excited states with high spin multiplicities, such as triplet or quintet states, have been revealed as key intermediates. The exploration of their properties and formation conditions is thus expected to provide invaluable insight into their underlying photophysics and promises to reveal strategies for increasing the performance of optoelectronic devices. However, accessing these high-multiplicity excited states of PDI to increase our mechanistic understanding remains a difficult task, due to the fact that the lowest excited singlet state of PDI decays with near-unity quantum yield to its ground state. Here we make use of radical-enhanced intersystem crossing (EISC) to generate the PDI triplet state in high yield. One or two 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) stable radicals were covalently attached to the imide position of PDI chromophores with and without p-tert-butylphenoxy core substituents. By combining femtosecond UV-vis transient absorption and transient electron paramagnetic resonance spectroscopies, we demonstrate strong magnetic exchange coupling between the PDI triplet state and TEMPO, resulting in the formation of excited quartet or quintet states. Important differences in the S1 state deactivation rate constants and triplet yields are observed for compounds bearing PDI moieties with different core substitution patterns. We show that these differences can be rationalized by considering the varying importance of competitive excited state decay processes, such as electron and excitation energy transfer. The comparison of the results obtained for different PDI-TEMPO derivatives leads us to propose design guidelines for optimizing the efficiency of triplet sensitization in molecular assemblies by EISC.

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Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states.

Publications

Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states.

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