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实验测得的荧光蛋白的单、双光子吸收光谱在低频和高频区域都表现出明显不同的特征。为了揭示这些不同点的起源和研究荧光蛋白的构–效关系,我们详细研究了三种荧光蛋白发色团(一种增强型蓝绿色荧光蛋白的中性发色团和两种红色荧光蛋白的阴离子发色团)的单、双光子吸收特性,分别计算了纯的和振动分辨的电子谱。计算结果表明:光谱线形与计算采用的交换相关密度泛函及谱截面计算所采用的近似关系密切;如果在计算光谱截面时,我们利用长程修正的交换相关泛函CAM-B3LYP来计算几何和电子结构参数,然后把Franck-Condon(FC)效应和包含Herzberg-Teller(HT)效果的电-声耦合效应都考虑进去,理论计算的光谱与实验测定的光谱可以很好地符合;对于两种离子态的发色团,HT电-声耦合效应使得对应于基态到第一激发态跃迁的双光子吸收最强峰相对于单光子吸收的最强峰发生了蓝移,但HT电-声耦合效应对高频的双光子吸收谱没有太大的影响;分子内电荷转移是导致高频区的双光子吸收明显强于单光子吸收的主要原因。
Experimentally measured single- and two-photon absorption spectra of fluorescent proteins show distinctly different characteristics in the low and high frequency regions. In order to reveal the origin of these differences and to investigate the structure-activity relationship of fluorescent proteins, we examined in detail three fluorescent protein chromophores, an enhanced neutral-chromophore of both cyan fluorescent protein and two red fluorescent proteins Anionic chromophores) single and two-photon absorption characteristics were calculated pure and vibration-resolved electron spectrum. The calculation results show that the spectral line shape is closely related to the exchange-dependent density functionalities used in the calculation and the approximation used in the calculation of the spectral cross-section. If we calculate the spectral cross-section, we use the long-distance-corrected exchange-related functional theory CAM-B3LYP to calculate the geometric and electronic Structure parameters and then take into account both the Franck-Condon (FC) effect and the electro-acoustic coupling effect including the Herzberg-Teller (HT) effect. The theoretical calculated spectra agree well with the experimentally measured spectra; for both ions State of the chromophore, HT electro-acoustic coupling effect makes the two-photon absorption peak corresponding to the first excited state transition from the ground state to the strongest peak of single photon absorption blue-shifted, but HT electro-acoustic coupling effect The two-photon absorption spectrum of high frequency has no significant effect; the intramolecular charge transfer is the main reason that the two-photon absorption in the high frequency region is obviously stronger than the single photon absorption.