Photophysical Properties of Intramolecular Charge Transfer in Two Newly Synthesized Tribranched Donor−π−Acceptor Chromophores

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• 作者：Mingli Jia ; Xiaonan Ma ; Linyin Yan ; Haifeng Wang ; Qianjin Guo ; Xuefei Wang ; Yingying Wang ; Xiaowei Zhan ; Andong Xia
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：July 15, 2010
• 年：2010
• 卷：114
• 期：27
• 页码：7345-7352
• 全文大小：296K
• 年卷期：v.114,no.27(July 15, 2010)
• ISSN：1520-5215

文摘

The nature of optical excitation and the degree of intramolecular charge transfer (ICT) as well as the dynamics of excited ICT states of two new tribranched donor−π−acceptor molecules with acceptor-terminated (DA₃) and acceptor-centered (AD₃) geometries have been investigated by steady-state and femtosecond time-resolved stimulated emission fluorescence depletion (FS TR-SEP FD) measurements in different polar solvents. The interpretation of the experimental results is based on the comparative investigation of the two D−π−A compounds with respect to the model monomer counterpart (DA). The larger solvatochromic effects and stronger solvent dependence of spectral properties of DA₃ than that of AD₃ indicate that the excited ICT state of DA₃ possesses higher polarity and larger dipole moments compared to those of AD₃. The similarity of absorption and strong solvent-dependent fluorescence spectra of DA₃ and DA reveals that the excited-state properties of DA₃ are identical to that of the model DA, which localized on one of the branches in DA₃. In contrast to DA₃, the large red shift in the absorption and the small Stokes shift of AD₃ suggest the formation of a delocalized ICT state to a certain extent in the excited state of AD₃. The dynamic behavior of excited ICT states for all three compounds are also investigated by femtosecond time-resolved stimulated emission depletion (FS TR-SEP FD) measurements, where the excited-state relaxations are highly dependent on both solvent polarity and the polar degree of the excited ICT states. Furthermore, the steady-state fluorescence excitation anisotropy shows that the intramolecular excitation transfer among the three disorder-induced localized ICT states with nondegenerate transition dipole moments is involved within DA₃. Compared to DA₃, a substantial red shift in the absorption of AD₃ results from the formation of a delocalized ICT state, where the specific excitation anisotropy spectrum shows that the excitation energy is mainly redistributed between the localized ICT state and the delocalized ICT state.