Alsaleh Ajyal Z, Pinjari Dilip, Misra Rajneesh, D'Souza Francis
Department of Chemistry, University of North Texas, Denton, TX 76203-5017, USA.
Department of Chemistry, Indian Institute of Technology, Indore, 453552, India.
Chemistry. 2023 Sep 21;29(53):e202301659. doi: 10.1002/chem.202301659. Epub 2023 Aug 17.
A far-red absorbing sensitizer, BF -chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push-pull systems linked with different nitrogenous electron donors, viz., N,N-dimethylaniline (NND), triphenylamine (TPA), and phenothiazine (PTZ) via an acetylene linker. The structural integrity of the newly synthesized push-pull systems was established by spectroscopic, electrochemical, spectroelectrochemical, and DFT computational methods. Cyclic and differential pulse voltammetry studies revealed different redox states and helped in the estimation of the energies of the charge-separated states. Further, spectroelectrochemical studies performed in a thin-layer optical cell revealed diagnostic peaks of azaBODIPY⋅ in the visible and near-IR regions. Free-energy calculations revealed the charge separation from one of the covalently linked donors to the azaBODIPY* to yield Donor⋅ -azaBODIPY⋅ to be energetically favorable in a polar solvent, benzonitrile, and the frontier orbitals generated on the optimized structures helped in assessing such a conclusion. Consequently, the steady-state emission studies revealed quenching of the azaBODIPY fluorescence in all of the investigated push-pull systems in benzonitrile and to a lesser extent in mildly polar dichlorobenzene, and nonpolar toluene. The femtosecond pump-probe studies revealed the occurrence of excited charge transfer (CT) in nonpolar toluene while a complete charge separation (CS) for all three push-pull systems in polar benzonitrile. The CT/CS products populated the low-lying azaBODIPY* prior to returning to the ground state. Global target (GloTarAn) analysis of the transient data revealed the lifetime of the final charge-separated states (CSS) to be 195 ps for NND-derived, 50 ps for TPA-derived, and 85 ps for PTZ-derived push-pull systems in benzonitrile.
一种远红光吸收敏化剂，硼氟螯合氮杂二吡咯甲烷（氮杂BODIPY）已被用作电子受体，通过乙炔连接基合成了一系列与不同含氮电子供体相连的推拉体系，即N，N - 二甲基苯胺（NND）、三苯胺（TPA）和吩噻嗪（PTZ）。通过光谱、电化学、光谱电化学和密度泛函理论（DFT）计算方法确定了新合成的推拉体系的结构完整性。循环伏安法和差分脉冲伏安法研究揭示了不同的氧化还原状态，并有助于估算电荷分离态的能量。此外，在薄层光学电池中进行的光谱电化学研究揭示了氮杂BODIPY⋅在可见光和近红外区域的诊断峰。自由能计算表明，在极性溶剂苄腈中，从一个共价连接的供体到氮杂BODIPY的电荷分离以生成供体⋅ - 氮杂BODIPY⋅在能量上是有利的，优化结构上产生的前沿轨道有助于评估这一结论。因此，稳态发射研究表明，在苄腈中，所有研究的推拉体系中氮杂BODIPY荧光均发生猝灭，在中等极性的二氯苯和非极性的甲苯中猝灭程度较小。飞秒泵浦 - 探测研究表明，在非极性甲苯中发生了激发电荷转移（CT），而在极性苄腈中所有三个推拉体系都发生了完全电荷分离（CS）。CT/CS产物在返回基态之前填充到低位的氮杂BODIPY。对瞬态数据的全局目标（GloTarAn）分析表明，在苄腈中，NND衍生的推拉体系的最终电荷分离态（CSS）寿命为195 ps，TPA衍生的为50 ps，PTZ衍生的为85 ps。
