The Q-Band Energetics and Relaxation of Chlorophylls <i>a</i> and <i>b</i> as Revealed by Visible-to-Near Infrared Time-Resolved Absorption Spectroscopy
Rong-Yao Gao, Jian‐Wei Zou, Yan‐Ping Shi, Dan-Hong Li, Junrong Zheng, Jianping Zhang
Abstract
Chlorophyll (Chl) is the most abundant light-harvesting pigment of oxygenic photosynthetic organisms; however, the Q-band energetics and relaxation dynamics remain unclear. In this work, we have applied femtosecond time-resolved ( fs -TA) absorption spectroscopy in 430–1,700 nm to Chls a and b in diluted pyridine solutions under selective optical excitation within their Q-bands. The results revealed distinct near-infrared absorption features of the B x,y ← Q y and B x,y ← Q x transitions in 930–1,700 nm, which together with the steady-state absorption in 400–700 nm unveiled the Q x(0,0) -state energy that lies 1,000 ± 400 and 600 ± 400 cm –1 above the Q y(0,0) -state for Chls a and b, respectively. In addition, the Q x -to-Q y internal conversion time constants are estimated to be less than 80 fs for Chls a and b . These findings may shed light on understanding the roles of the Chls in the primary excitation energy transfer reactions of photosynthesis.