AbstractA far‐red absorbing sensitizer, BF2‐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 1azaBODIPY* 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 3azaBODIPY* 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.
摘要 以远红外线吸收敏化剂--
BF2-螯合偶氮二
吡喃
甲烷(azadipyrromethane,azBODIPY)为电子受体,通过
乙炔连接物与不同的含氮电子供体--
N,N-二甲基苯胺(NND)、
三苯胺(
TPA)和
吩噻嗪(
PTZ)--连接,合成了一系列推挽体系。通过光谱、电
化学、光谱电
化学和 DFT 计算方法确定了新合成的推挽系统的结构完整性。循环和微分脉冲伏安研究揭示了不同的氧化还原状态,并有助于估算电荷分离状态的能量。此外,在薄层光学电池中进行的光谱电
化学研究揭示了 azaBODIPY⋅- 在可见光和近红外区域的诊断峰。自由能计算显示,在极性溶剂苯腈中,从共价连接的供体之一到 1azaBODIPY* 的电荷分离产生供体⋅+-azaBODIPY⋅- 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
苯甲腈中,所有被研究的推挽系统都会淬灭 azaBODIPY 荧光,在轻度极性的二
氯苯和非极性的
甲苯中也会淬灭少量荧光。飞秒泵探针研究显示,在非极性
甲苯中发生了激发电荷转移(CT),而在极性
苯甲腈中,所有三种推挽系统都发生了完全的电荷分离(CS)。CT/CS 产物在返回基态之前填充了低洼的 3azaBODIPY* 。对瞬态数据的全局目标 (GloTarAn) 分析表明,在
苯甲腈中,NND 衍生的最终电荷分离态 (CSS) 的寿命为 195 ps,
TPA 衍生的为 50 ps,
PTZ 衍生的为 85 ps。