Graduate School of Information Science, Nagoya University, Nagoya, Japan.
Photochem Photobiol. 2012 Jul-Aug;88(4):889-98. doi: 10.1111/j.1751-1097.2012.01126.x. Epub 2012 Mar 28.
The absorption and fluorescence spectra of firefly luciferin, which is an analog of oxyluciferin, are investigated by performing the density functional theory (DFT) calculations, especially focusing on the experimentally unassigned peaks. Time-dependent DFT calculations are performed for the excited states of firefly luciferin and its conjugate acids and bases. We find that (1) the peaks in the experimental absorption spectra correspond to the excited states of not only (6'O(-), 4COO(-)) and (6'OH, 4COO(-)), but also (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (2) the peaks in the experimental fluorescence spectra correspond to the excited states of not only (6'O(-), 4COO(-)), but also (6'OH, 4COO(-)), (6'O(-), 4COOH), (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (3) the unassigned peak near 400 nm in the experimental absorption spectra at pH 1 is assigned to the absorption from the equilibrium ground state to the first excited state of (6'OH, 3H(+), 4COOH); and (4) the unassigned peak at 610 nm in the experimental fluorescence spectra corresponds to the transition from the equilibrium first excited state to the ground state of (6'OH, 4COO(-)).
我们通过执行密度泛函理论（DFT）计算，研究了萤火虫荧光素（一种氧化荧光素的类似物）的吸收和荧光光谱，尤其关注实验上未分配的峰。我们对萤火虫荧光素及其共轭酸碱的激发态进行了时间依赖的 DFT 计算。我们发现：（1）实验吸收光谱中的峰对应于（6'O(-)，4COO(-)）和（6'OH，4COO(-)）的激发态，还对应于（6'OH，4COOH）和（6'OH，3H(+)，4COOH）的激发态；（2）实验荧光光谱中的峰对应于（6'O(-)，4COO(-)）和（6'OH，4COO(-)）、（6'O(-)，4COOH）、（6'OH，4COOH）和（6'OH，3H(+)，4COOH）的激发态；（3）在 pH 1 时实验吸收光谱中 400nm 附近未分配的峰被分配到（6'OH，3H(+)，4COOH）的平衡基态到第一激发态的吸收；（4）实验荧光光谱中 610nm 处的未分配峰对应于（6'OH，4COO(-)）的平衡第一激发态到基态的跃迁。
