LIDYL, CEA, CNRS , Université Paris-Saclay, CEA Saclay , 91191 Gif-sur-Yvette , France.
Laboratory of Innovation in Surface Chemistry and Nanosciences (LICSEN), NIMBE, CEA, CNRS , Université Paris-Saclay , CEA Saclay, 91191 Gif-sur-Yvette Cedex , France.
J Phys Chem A. 2018 Jun 28;122(25):5533-5544. doi: 10.1021/acs.jpca.8b05177. Epub 2018 Jun 13.
There is a high interest in the development of new push-pull dyes for the use in dye sensitized solar cells. The pronounced charge transfer character of the directly photoexcited state is in principle favorable for a charge injection. Here, we report a time-resolved fluorescence study of a triphenylamine-bithiophene-naphthalimide dye in four solvents of varying polarity using fluorescence upconversion. The recording of femtosecond time-resolved fluorescence spectra corrected for the group velocity dispersion allows for a detailed analysis discriminating between spectral shifts and total intensity decays. After photoexcitation, the directly populated state (S/FC) evolves toward a relaxed charge transfer state (S/CT). This S/CT state is characterized by a lower radiative transition moment and a higher nonradiative quenching. The fast dynamic shift of the fluorescence band is well described by solvation dynamics in polar solvents, but less so in nonpolar solvents, hinting that the excited-state relaxation process occurs on a free energy surface whose topology is strongly governed by the solvent polarity. This study underlines the influence of the environment on the intramolecular charge transfer (ICT) process, and the necessity to analyze time-resolved data in detail when solvation and ICT occur simultaneously.
人们对于开发新型推拉染料以应用于染料敏化太阳能电池有着浓厚的兴趣。直接光激发态的显著电荷转移特性原则上有利于电荷注入。在这里，我们使用荧光上转换法，在四种不同极性的溶剂中，对三苯胺-联噻吩-萘酰亚胺染料进行了时间分辨荧光研究。对群速度色散进行校正的飞秒时间分辨荧光光谱的记录，允许对光谱位移和总强度衰减进行详细的分析。光激发后，直接填充的激发态（S/FC）向弛豫的电荷转移态（S/CT）演变。S/CT 态的辐射跃迁矩较低，非辐射猝灭较高。荧光带的快速动态位移很好地描述了极性溶剂中的溶剂化动力学，但在非极性溶剂中则不然，这表明激发态弛豫过程发生在自由能表面上，该表面的拓扑结构强烈受溶剂极性的控制。这项研究强调了环境对分子内电荷转移（ICT）过程的影响，并强调了在溶剂化和 ICT 同时发生时，必须详细分析时间分辨数据。
