Sun Jifu, Li Weixu, Hou Yuqi, Zhang Xue, Gao Zhongzheng, Wang Bo, Zhao Jianzhang
College of Chemical and Biological Engineering, Shandong University of Science and Technology, J2-424, 579 Qianwangang Road, Qingdao 266590, P. R. China.
State Key Laboratory of Fine Chemicals, Dalian University of Technology, 2 Ling-Gong Road, Dalian 116024, P. R. China.
ACS Omega. 2021 Oct 14;6(42):28356-28365. doi: 10.1021/acsomega.1c04540. eCollection 2021 Oct 26.
Weakening the triplet-triplet annihilation (TTA) self-quenching effect induced by sensitizers remains a tremendous challenge due to the very few investigations carried out on them. Herein, benzo-21-crown-7 ()-functionalized 2,6-diiodo-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene () was synthesized to investigate the influences of huge bulks and electron-rich cavities of moieties on the fluorescence emission and triplet-state lifetimes of moieties. Density functional theory (DFT)/time-dependent DFT (TDDFT) computable results preliminarily predicted that moieties had influences on the fluorescence emissions of moieties but not on their localization of triplet states of -functionalized (). The UV-vis absorption spectra, fluorescence emission spectra, and cyclic voltammograms verified that there was an electron-transfer process from the moiety to the moiety in . However, the calculated results of Δ and values and nanosecond time-resolved transient absorption spectra demonstrated that the electron-transfer process from the moiety to the moiety in had direct influences on the fluorescence emission of moieties but not on the triplet states of moieties. The experimental values of triplet-state lifetimes of were obviously longer than those of at a high concentration (1.0 × 10 M); however, the fitted values of intrinsic triplet-state lifetimes of were slightly greater than those of in the same solvent. These results demonstrated that the steric hindrance of moieties could weaken the TTA self-quenching effect of moieties at a high concentration and the a-PET effect induced a proportion of the produced singlet states of moieties and could not emit fluorescence in the form of radiation transition but they could be transformed into triplet states through intersystem crossing (ISC) processes due to the iodine atoms in the moiety. The stronger a-PET effects in polar solvents induced smaller fluorescence quantum yields so that more singlet states of moieties were transformed into triplet states to weaken the TTA self-quenching effects.
由于对敏化剂诱导的三重态-三重态湮灭（TTA）自猝灭效应的研究非常少，削弱这种效应仍然是一个巨大的挑战。在此，合成了苯并-21-冠-7（）功能化的2,6-二碘-1,3,5,7-四甲基-8-苯基-4,4-二氟硼二氮杂萘（），以研究基团的大体积和富电子空腔对基团荧光发射和三重态寿命的影响。密度泛函理论（DFT）/含时密度泛函理论（TDDFT）的计算结果初步预测，基团对基团的荧光发射有影响，但对功能化（）的三重态定位没有影响。紫外-可见吸收光谱、荧光发射光谱和循环伏安图证实，在中存在从基团到基团的电子转移过程。然而，Δ和值的计算结果以及纳秒时间分辨瞬态吸收光谱表明，中从基团到基团的电子转移过程对基团的荧光发射有直接影响，但对基团的三重态没有影响。在高浓度（1.0×10 M）下，的三重态寿命实验值明显长于；然而，在相同溶剂中，的本征三重态寿命拟合值略大于。这些结果表明，基团的空间位阻在高浓度下可以削弱基团的TTA自猝灭效应，且a-PET效应诱导了一部分基团产生的单重态，这些单重态不能以辐射跃迁的形式发射荧光，但由于基团中的碘原子，它们可以通过系间窜越（ISC）过程转化为三重态。极性溶剂中较强的a-PET效应导致较小的荧光量子产率，从而使更多的基团单重态转化为三重态，削弱TTA自猝灭效应。
