Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom.
Cell Biophysics Laboratory, Ikerbasque, Basque Foundation for Science and Unidad de Biofisica (CSIC-UPV/EHU), Bilbao, Spain.
J Chem Phys. 2018 Apr 7;148(13):134311. doi: 10.1063/1.5011642.
In this work, we present a complete theoretical description of the excited state order created by two-photon photoselection from an isotropic ground state; this encompasses both the conventionally measured quadrupolar (K = 2) and the "hidden" degree of hexadecapolar (K = 4) transition dipole alignment, their dependence on the two-photon transition tensor and emission transition dipole moment orientation. Linearly and circularly polarized two-photon absorption (TPA) and time-resolved single- and two-photon fluorescence anisotropy measurements are used to determine the structure of the transition tensor in the deprotonated form of enhanced green fluorescent protein. For excitation wavelengths between 800 nm and 900 nm, TPA is best described by a single element, almost completely diagonal, two-dimensional (planar) transition tensor whose principal axis is collinear to that of the single-photon S → S transition moment. These observations are in accordance with assignments of the near-infrared two-photon absorption band in fluorescent proteins to a vibronically enhanced S → S transition.
在这项工作中，我们提出了一个完整的理论描述，描述了由各向同性基态的双光子光选择激发产生的激发态序；这包括通常测量的四极（K=2）和“隐藏”的十六极（K=4）跃迁偶极子取向，它们依赖于双光子跃迁张量和发射跃迁偶极子取向。线性和圆偏振双光子吸收（TPA）和时间分辨单光子和双光子荧光各向异性测量用于确定去质子化形式的增强型绿色荧光蛋白中跃迁张量的结构。对于 800nm 到 900nm 的激发波长，TPA 最好由一个几乎完全对角的二维（平面）跃迁张量来描述，其主轴与单光子 S→S 跃迁矩的主轴共线。这些观察结果与荧光蛋白中近红外双光子吸收带的分配相一致，即振动态增强的 S→S 跃迁。
