含绿色荧光蛋白发色团双自由基分子的非线性光学性质

Nonlinear Optical Properties of Green Fluorescent Protein Chromophore Coupled Diradicals

采用密度泛函理论(DFT)方法研究了系列含绿色荧光蛋白发色团双自由基分子光学异构体的几何结构、极化率(αs)和第一超极化率(βtot).结果表明,引入电子给受体取代基使分子的极化率增大,而对第一超极化率有不同影响.对于光照前的反式结构,引入电子受体βtot值增加,且βtot值随取代基吸电子能力的增强而增大;引入电子给体βtot值降低,且βtot值随取代基给电子能力的增强而减小.当分子变成相应的顺式结构时,其βtot值变化趋势与反式结构的结果正好相反.光异构化前后分子的βtot值变化不同,引入电子受体使顺式结构的βtot值比反式结构的小,其中―NO2使顺式结构的βtot值减小为反式结构的1/6;引入电子给体使反式结构的βtot值比顺式结构的小,其中―NH2使反式结构的βtot值减小为顺式结构的1/6.从而,光异构化起到调节非线性光学(NLO)响应的作用.

The geometries, polarizabilities （as）, and first hyperpolarizabilities （βtot） of a series of green fluorescent protein chromophore coupled diradicals and their corresponding optical isomers were investigated using density functional theory （DFT）. The results show that the introductions of the electron donor/acceptor significantly enhance the polarizabilities and have a different influence on the first hyperpolarizabilities. For trans isomers, the ,βtot values of the studied compounds increase with increasing strength of the electron-withdrawing ability of the substituent, whereas the ,Sto, values decrease significantly with increasing strength of the electron-donating ability of the substituent. For cis isomers, the trends in the changes in the ,βtot, values are the opposite of those for trans isomers on introduction of a donor/acceptor. Significantly, photoisomerization can lead to the different ,βtot values. The ,sto, values of cis isomers are smaller than those of trans isomers when electron acceptors are introduced. For example, the ,βtot, value of the cis isomer with the strongest electron acceptor, i.e., -NO2, is about 1/6 that of the corresponding trans isomer. However, the ,βtot, values of trans isomers are smaller than those of cis isomers when electron donors are introduced. For example, the ,8,ot value of the trans isomer with the strongest electron donor, i.e., --NH2, is about six times smaller than that of the corresponding cis isomer. As a result, photoisomerization can modulate the molecular nonlinear optical （NLO） responses effectively.