Photoinduced intramolecular charge transfer and S2 fluorescence in thiophene-pi-conjugated donor-acceptor systems: experimental and TDDFT studies.
Experimental and theoretical methods were used to study newly synthesized thiophene-pi-conjugated donor-acceptor compounds, which were found to exhibit efficient intramolecular charge-transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert-Mataga models. We found that intramolecular charge transfer in these donor-acceptor systems is significantly dependent on the electron-withdrawing substituents at the thienyl 2-position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge-transfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric conformations. In addition, a novel S(2) fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S(2) fluorescence. We demonstrate that S(2) fluorescence can be explained by the calculated energy gap between the S(2) and S(1) states of these molecules. Furthermore, nonlinear optical behavior of the thiophene-pi-conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.
Zhao
Guang-Jiu
GJ
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, China. gjzhao@dicp.ac.cn
Chen
Rui-Kui
RK
Sun
Meng-Tao
MT
Liu
Jian-Yong
JY
Li
Guang-Yue
GY
Gao
Yun-Ling
YL
Han
Ke-Li
KL
Yang
Xi-Chuan
XC
Sun
Licheng
L