醌型D-π-A类化合物AMTOE在不同溶剂中吸收和发射光谱的蓝移现象

Theoretical study on negative solvatochromism of zwitterionic D-π-A compound in solvents of different polarity

采用连续介质模型(PCM)以及明确/连续的混合溶剂模型,运用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)方法,研究了溶剂极性对D-π-A类两性离子化合物1-(4-aza-4-methylphenyl)-2-trans-(4-oxyphenyl)ethane(AMTOE)分子几何、电子结构以及光谱性质的影响.计算结果表明,随着溶剂极性和超分子簇大小的增加,AMTOE基态(S0)分子几何从醌式结构向芳式结构转化.从基态(S0)到激发态(S1),化合物AMTOE醌式结构增强.从弱极性的氯仿溶液到强极性的水溶液,AMTOE分子的吸收光谱和发射光谱均发生蓝移,并且吸收光谱的蓝移程度大于发射光谱的蓝移程度,与实验现象定性一致.吸收光谱和发射光谱发生蓝移的原因是随着溶剂极性增强,HOMO轨道能级与LUMO轨道能级之间的能隙增大.对于具有明显电荷转移的AMTOE分子的溶剂化显色效应,长程矫正的含时密度泛函TD-CAM-B3LYP方法比传统的含时密度泛函TD-B3LYP方法更为合理.另外,明确/连续的混合溶剂模型能更好的描述该类体系在强极性溶剂中的溶剂化显色效应.

The solvent effects on the molecular geometry, electronic structure, and the spectral properties of intramolecular charge transfer of zwitterionic compound, 1-（4-aza-4-methylphenyl）- 2- trans-（4-oxyphenyl）-ethane（AMTOE） were investigated by density functional theory（DFT） and time-dependent density functional theory（TD-DFT） calculations. Both the continuum dielectric model and the combined discrete/continuum strategy were employed. The ground- and lowest-dipole allowed singlet excited-state electronic structures of AMTOE in CHCl_3, CH_3 CN, and H_2 O solvents were investigated through DFT and TD-DFT methods at the PCM-CAM-B3LYP/6-31＋G＊＊ level. The results suggest that the quinoid structures of the ground-state geometries are transformed into aromatic structures with increasing the medium polarity. And the quinoid structure of AMTOE is enhanced from S_0 to S_1. It has been observed that both the maximum wavelengths of absorption and emission spectra of AMTOE undergo a blue shift with increasing the solvent polarity, while the degree of negative solvatochromic shift of absorption spectra is more significant than that of emission spectra as the solvent polarity increasing and is in agreement with experimental observations. The different extent of solvation of HOMO and LUMO may rationalize the blue shift of the absorption spectra and emission spectra of AMTOE from less polar to highly polar solvents. It is also demonstrated that the long-range corrected functional, CAM-B3 LYP gives better agreement with the experimental spectrums for such significant intramolecular charge-transfer AMTOE system than B3 LYP functional. And the combined discrete/continuum model can describe well the absorption spectra of AMTOE compound in solutions and is well reproduce the solvatochromic shifts of the AMTOE compound in strong polar solvents such as water.