State Key Laboratory of Fine Chemicals, Dalian University of Technology , E-208 West Campus, 2 Ling-Gong Road, Dalian 116024, People's Republic of China.
Dipartimento di Scienze Chimiche, Università degli Studi di Padova , Via Marzolo, 1, 35131 Padova, Italy.
J Am Chem Soc. 2017 Jun 14;139(23):7831-7842. doi: 10.1021/jacs.7b02063. Epub 2017 Jun 2.
A long-lived triplet excited state of the well-known fluorophore boron dipyrromethene (Bodipy) was observed for the first time via efficient radical-enhanced intersystem crossing (EISC). The triplet state has been obtained in two dyads in which the Bodipy unit is linked to a nitroxide radical, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), with two different length spacers. The photophysical properties were studied with steady-state and time-resolved transient optical spectroscopies and electron spin resonance (cw-ESR and TR-ESR). The fluorescence of Bodipy units is significantly quenched in the dyads, and the spin-polarized TEMPO signals were observed with TR-ESR, generated by a radical triplet pair mechanism. Efficient EISC (Φ = 80%) was observed for the dyad with a shorter linker, and the triplet state lifetime of the Bodipy chromophore is exceptionally long (62 μs). The EISC takes 250 ps. Poor ISC was observed for the dyad with a longer linker. The efficient ISC and long-lived triplet excited state in this flexible system are in stark contrast to the previously studied rigid EISC systems. The EISC effect was employed for the first time to perform triplet-triplet annihilation (TTA) upconversion (quantum yield Φ = 6.7%).
首次通过有效的自由基增强系间窜越（EISC）观察到著名荧光团硼二吡咯亚甲基（Bodipy）的长寿命三重态激发态。该三重态状态已在两个二聚体中获得，其中Bodipy 单元与氮氧自由基 2,2,6,6-四甲基-1-哌啶氧基（TEMPO）相连，具有两个不同长度的间隔基。通过稳态和时间分辨瞬态光学光谱和电子自旋共振（cw-ESR 和 TR-ESR）研究了光物理性质。二聚体中的 Bodipy 单元的荧光显著猝灭，并且通过自由基三重态对机制生成了 TR-ESR，观察到了自旋极化的 TEMPO 信号。对于具有较短连接基的二聚体，观察到有效的 EISC（Φ=80%），并且 Bodipy 发色团的三重态寿命非常长（62μs）。EISC 发生需要 250 ps。对于具有较长连接基的二聚体，ISC 效率较差。在这个灵活的系统中，有效的 ISC 和长寿命三重态激发态与以前研究的刚性 EISC 系统形成鲜明对比。首次将 EISC 效应用于进行三重态-三重态湮灭（TTA）上转换（量子产率Φ=6.7%）。
