Chen Fangyi, Zhang Wanxi, Liu Zijian, Meng Lingyan, Bai Binglian, Wang Haitao, Li Min
Key Laboratory of Automobile Materials (MOE), College of Materials Science and Engineering, Jilin University Changchun 130012 China
College of Physics, Jilin University Changchun 130012 China.
RSC Adv. 2018 Dec 19;9(1):1-10. doi: 10.1039/c8ra08439d.
The intramolecular charge transfer characteristic of two diphenylamine substituted symmetric 1,3,4-oxadiazole derivatives (DPAOXD and DPAOXDBEN) was studied through a combination of experimental techniques and theoretical calculations. Significant enhancement of intramolecular charge transfer strength has been found in both these compounds through molecular structure modification. The experimental result found only a small red shift in the absorption spectra (∼15 nm) but a very large red shift in the emission spectra (∼114 nm for DPAOXD and ∼140 nm for DPAOXDBEN) with increasing solvent polarity, indicating a large extent charge transfer occurred in their excited state. The increase of molecular dipole moment from the ground state to the charge transfer excited state is calculated to be 22.10 D in DPAOXD and 26.67 D in DPAOXDBEN, respectively. Theoretical calculations present clear evidence that electrons transfer from the terminal diphenylamine to the bi-1,3,4-oxadiazole rings in DPAOXD, and the two 1,3,4-oxadiazole rings and central benzene ring in DPAOXDBEN. As compared to the methoxy group, the substitution by a diphenylamine group could increase both the transferred charge and distance, which could substantially strengthen the charge transfer character. Further introduction of a central benzene ring in DPAOXDBEN could further increase the transferred distance, and then the charge transfer strength. These findings could provide good guidance for the design of molecules with high intramolecular charge transfer characteristics.
通过实验技术和理论计算相结合的方法，研究了两种二苯胺取代的对称1,3,4 - 恶二唑衍生物（DPAOXD和DPAOXDBEN）的分子内电荷转移特性。通过分子结构修饰，发现这两种化合物的分子内电荷转移强度均有显著增强。实验结果表明，随着溶剂极性的增加，吸收光谱仅出现小的红移（约15 nm），而发射光谱出现非常大的红移（DPAOXD约为114 nm，DPAOXDBEN约为140 nm），这表明在其激发态发生了很大程度的电荷转移。计算得出，从基态到电荷转移激发态，DPAOXD的分子偶极矩增加量为22.10 D，DPAOXDBEN为26.67 D。理论计算提供了明确的证据，表明在DPAOXD中电子从末端二苯胺转移到双1,3,4 - 恶二唑环，在DPAOXDBEN中电子从末端二苯胺转移到两个1,3,4 - 恶二唑环和中心苯环。与甲氧基相比，用二苯胺基团取代可增加转移电荷和转移距离，从而显著增强电荷转移特性。在DPAOXDBEN中进一步引入中心苯环可进一步增加转移距离，进而增强电荷转移强度。这些发现可为设计具有高分子内电荷转移特性的分子提供良好的指导。
