Liu Heyuan, Ruan Meixia, Mao Pengcheng, Wang Zhuan, Chen Hailong, Weng Yuxiang
The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
School of Physical Science, University of the Chinese Academy of Sciences, Beijing 100049, China.
J Chem Phys. 2024 May 28;160(20). doi: 10.1063/5.0203819.
Understanding the dynamics of excited-state vibrational energy relaxation in photosynthetic pigments is crucial for elucidating the mechanisms underlying energy transfer processes in light-harvesting complexes. Utilizing advanced femtosecond broadband transient fluorescence (TF) spectroscopy, we explored the excited-state vibrational dynamics of Chlorophyll-a (Chl-a) both in solution and within the light-harvesting complex II (LHCII). We discovered a vibrational cooling (VC) process occurring over ∼6 ps in Chl-a in ethanol solution following Soret band excitation, marked by a notable ultrafast TF blueshift and spectral narrowing. This VC process, crucial for regulating the vibronic lifetimes, was further elucidated through the direct observation of the population dynamics of higher vibrational states within the Qy electronic state. Notably, Chl-a within LHCII demonstrated significantly faster VC dynamics, unfolding within a few hundred femtoseconds and aligning with the ultrafast energy transfer processes observed within the complex. Our findings shed light on the complex interaction between electronic and vibrational states in photosynthetic pigments, underscoring the pivotal role of vibrational dynamics in enabling efficient energy transfer within light-harvesting complexes.
了解光合色素中激发态振动能量弛豫的动力学过程对于阐明光捕获复合物中能量转移过程的潜在机制至关重要。利用先进的飞秒宽带瞬态荧光（TF）光谱技术，我们研究了叶绿素-a（Chl-a）在溶液中和光捕获复合物II（LHCII）中的激发态振动动力学。我们发现，在索雷特带激发后，乙醇溶液中的Chl-a在约6皮秒内发生了振动冷却（VC）过程，其特征是显著的超快TF蓝移和光谱变窄。通过直接观察Qy电子态内较高振动态的布居动力学，进一步阐明了这一对于调节振动电子寿命至关重要的VC过程。值得注意的是，LHCII中的Chl-a表现出明显更快的VC动力学，在几百飞秒内完成，并与复合物中观察到的超快能量转移过程相一致。我们的研究结果揭示了光合色素中电子态与振动态之间的复杂相互作用，强调了振动动力学在光捕获复合物中实现高效能量转移的关键作用。
