The excited-state dynamics of the GFP chromophore, HBDI^– (anionic p-hydroxybenzylidene-2,3-dimethylimidazolinone), were investigated through a combination of theoretical nonadiabatic molecular dynamics (NAMD) simulations and femtosecond transient absorption spectroscopy (fs-TA). The NAMD simulations revealed that the primary dynamics in excited states involve the formation of a P-twisted intermediate (S_1min,P), which undergoes pendulum-like oscillations with respect to ϕ = 90°. This motion serves as a reservoir for the excited-state population and the primary source of fluorescence. Rather than a direct channel from the major S_1min,P, a coordinated pathway of S_1min,P → S_1min → S_1min,I → S₀ is responsible for the decay to the ground state, emphasizing the importance of planar intermediate (S_1min) formation. The experimental fs-TA spectra confirmed these dynamics, revealing three distinct time scales (340–470 fs, 1.4 ps, and 8.3 ps), corresponding to the formation of S_1min,P and its decay governed by the coordinated pathway. At low temperatures, the coordinated decay pathway is suppressed, leading to prolonged fluorescence lifetimes, consistent with low-temperature experimental results. This study presents a new model for the excited-state dynamics of GFP chromophore, suggesting that pendulum motion and the coordinated decay pathway play a crucial role in regulating fluorescence intensity.

中文翻译：

---

绿色荧光蛋白 （GFP） 发色团的温度控制衰减和钟摆动力学


通过结合理论非绝热分子动力学 （NAMD） 模拟和飞秒瞬态吸收光谱 （fs-TA） 研究了 GFP 发色团 ^HBDI-（阴离子对羟基苄基-2,3-二甲基咪唑啉酮）的激发态动力学。NAMD 模拟表明，激发态下的主要动力学涉及 P 扭曲中间体 （S_{1 min，P}） 的形成，该中间体相对于 φ = 90° 发生钟摆状振荡。这种运动是激发态种群的储存库和荧光的主要来源。而不是从主要 S_1min，P 的直接通道，S_1min，P → S_1min → S_1min，I → S₀ 负责衰变为基态，强调了平面中间体 （S_1min 的重要性） 形成。实验 fs-TA 光谱证实了这些动力学，揭示了三个不同的时间尺度（340-470 fs、1.4 ps 和 8.3 ps），对应于 S_{1 min，P} 的形成及其由协调途径控制的衰变。在低温下，配位衰变途径受到抑制，导致荧光寿命延长，这与低温实验结果一致。本研究提出了一种 GFP 发色团激发态动力学的新模型，表明摆锤运动和协调衰变途径在调节荧光强度中起着至关重要的作用。