Photophysical properties of photoactive molecules with conjugated push-pull structures
Photophysical properties of photoactive molecules with conjugated push-pull structures
复制标题
DOI：
10.1021/jp0705323
复制
发表时间：
2007-07-05
影响因子：
2.9
通讯作者：
Bai, Fenglian
中科院分区：
文献类型：
--
作者：
Gong, Ying;Guo, Xunmin;Bai, Fenglian
采用稳态和飞秒荧光衰减测量方法研究了两种新合成的具有不对称D-pi-A结构和对称D-pi-A-pi-D结构的光活性化合物在不同非质子溶剂中的光物理性质.结果表明，不对称DA化合物在激发时的偶极矩变化比对称DAD化合物大，并利用Lippert-Mataga方程估算了这两种化合物的偶极矩。稳态光谱结果表明，随着溶剂极性的增加，它们的最大吸收峰发生了小的溶剂化变色位移，但荧光峰发生了大的红移，说明它们的偶极矩变化主要反映了激发态的偶极矩变化，而不是基态的偶极矩变化.红移的荧光带归因于光激发时的分子内电荷转移（ICT）状态，这可能导致与周围溶剂的强烈相互作用，从而引起快速溶剂重组。对称化合物的ICT状态比不对称化合物的极性小，表明激发态溶质-溶剂相互作用的稳定程度不同。飞秒荧光损耗测量进一步调查的快速溶剂化效应和动力学的ICT状态，这两个新的化合物。飞秒荧光耗尽结果表明，DA化合物比DAD化合物具有更快的溶剂化时间，这对应于弛豫ICT态的形成（即，溶剂化后溶剂分子重排的最终ICT状态）。因此，可以合理地理解，与那些对称化合物（D-pi-A-pi-D）相比，具有不对称（D-pi-A）结构的ICT化合物对于那些强烈依赖于电子推拉能力的性质的光伏器件具有更好的性能。
The photophysical properties of two newly synthesized photoactive compounds with asymmetrical D-pi-A structure and symmetrical D-pi-A-pi-D structure are investigated in different aprotic solvents by steady-state and femtosecond fluorescence depletion measurements. It is found that the asymmetrical DA compound has larger dipole moment change than that of the symmetrical DAD compound upon excitation, where the dipole moments of the two compounds have been estimated using the Lippert-Mataga equation. Furthermore, the steady-state spectral results show that increasing solvent polarity results in small solvatochromic shift in the absorption maxima but a large red shift in the fluorescence maxima for them, indicating that the dipole moment changes mainly reflect the changes of dipole moment in excited-state rather than in ground state. The red-shifted fluorescence band is attributed to an intramolecular charge transfer (ICT) state upon photoexcitation, which could result in a strong interaction with the surrounding solvents to cause the fast solvent reorganization. The resulting ICT states of symmetrical compounds are less polar than the asymmetrical compounds, indicating the different extents of stabilization of solute-solvent interaction in the excited state. Femtosecond fluorescence depletion measurements are further employed to investigate the fast solvation effects and dynamics of the ICT state of these two novel compounds. The femtosecond fluorescence depletion results show that the DA compound has faster solvation time than that of DAD compound, which corresponds to the formation of relaxed ICT state (i.e., a final ICT state with rearranged solvent molecules after solvation) in polar solvents. It is therefore reasonably understood that the ICT compounds with asymmetrical (D-pi-A) structure have better performance for those photovoltaic devices, which strongly rely on the nature of the electron push-pull ability, compared to those symmetrical compounds (D-pi-A-pi-D).