State Key Laboratory of Fine Chemicals, Frontier Science Center for Smart Materials, School of Chemical Engineering, Dalian University of Technology, 2 Ling Gong Road, Dalian 116024, China.
Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center of Russian Academy of Sciences, Kazan 420029, Russia.
Int J Mol Sci. 2023 Jul 7;24(13):11220. doi: 10.3390/ijms241311220.
We prepared a rhodamine-TEMPO chromophore-radical dyad (RB-TEMPO) to study the radical enhanced intersystem crossing (REISC). The visible light-harvesting chromophore rhodamine is connected with the TEMPO (a nitroxide radical) via a C-N bond. The UV-vis absorption spectrum indicates negligible electron interaction between the two units at the ground state. Interestingly, the fluorescence of the rhodamine moiety is strongly quenched in RB-TEMPO, and the fluorescence lifetime of the rhodamine moiety is shortened to 0.29 ns, from the lifetime of 3.17 ns. We attribute this quenching effect to the intramolecular electron spin-spin interaction between the nitroxide radical and the photoexcited rhodamine chromophore. Nanosecond transient absorption spectra confirm the REISC in RB-TEMPO, indicated by the detection of the rhodamine chromophore triplet excited state; the lifetime was determined as 128 ns, which is shorter than the native rhodamine triplet state lifetime (0.58 μs). The zero-field splitting (ZFS) parameters of the triplet state of the chromophore were determined with the pulsed laser excited time-resolved electron paramagnetic resonance (TREPR) spectra. RB-TEMPO was used as a photoinitiator for the photopolymerization of pentaerythritol triacrylate (PETA). These studies are useful for the design of heavy atom-free triplet photosensitizers, the study of the ISC, and the electron spin dynamics of the radical-chromophore systems upon photoexcitation.
我们制备了一种罗丹明-TEMPO 生色团-自由基偶联物（RB-TEMPO），以研究自由基增强的系间窜越（REISC）。可见光敏生色团罗丹明通过 C-N 键与 TEMPO（一种氮氧自由基）相连。紫外-可见吸收光谱表明，在基态下两个单元之间几乎没有电子相互作用。有趣的是，RB-TEMPO 中罗丹明部分的荧光被强烈猝灭，罗丹明部分的荧光寿命从 3.17 ns 缩短到 0.29 ns。我们将这种猝灭效应归因于氮氧自由基和光激发罗丹明生色团之间的分子内电子自旋-自旋相互作用。纳秒瞬态吸收光谱证实了 RB-TEMPO 中的 REISC，通过检测罗丹明生色团三重态激发态来证实；寿命确定为 128 ns，短于天然罗丹明三重态寿命（0.58 μs）。通过脉冲激光激发的时间分辨电子顺磁共振（TREPR）光谱确定了生色团三重态的零场分裂（ZFS）参数。RB-TEMPO 被用作五倍子三丙烯酸酯（PETA）光聚合的光引发剂。这些研究对于设计不含重原子的三重态光敏剂、ISC 研究以及光激发下自由基-生色团体系的电子自旋动力学都很有用。
