Assignment of the Q-bands of the chlorophylls: coherence loss via Qx - Qy mixing.
We provide a new and definitive spectral assignment for the absorption, emission, high-resolution fluorescence excitation, linear dichroism, and/or magnetic circular dichroism spectra of 32 chlorophyllides in various environments. This encompases all data used to justify previous assignments and provides a simple interpretation of unexplained complex decoherence phenomena associated with Qx → Qy relaxation. Whilst most chlorophylls conform to the Gouterman model and display two independent transitions Qx (S2) and Qy (S1), strong vibronic coupling inseparably mixes these states in chlorophyll-a. This spreads x-polarized absorption intensity over the entire Q-band system to influence all exciton-transport, relaxation and coherence properties of chlorophyll-based photosystems. The fraction of the total absorption intensity attributed to Qx ranges between 7% and 33%, depending on chlorophyllide and coordination, and is between 10% and 25% for chlorophyll-a. CAM-B3LYP density-functional-theory calculations of the band origins, relative intensities, vibrational Huang-Rhys factors, and vibronic coupling strengths fully support this new assignment.
School of Chemistry, The University of Sydney, 2006, NSW, Australia.
Jeffrey R
JR
Reimers
Zheng-Li
ZL
Cai
Rika
R
Kobayashi
Margus
M
Rätsep
Arvi
A
Freiberg
Elmars
E
Krausz
D000042:Absorption; D002734:Chlorophyll / Q000737:chemistry*; D002942:Circular Dichroism; D004986:Ether / Q000737:chemistry; D060328:Magnetic Phenomena; D055620:Optical Phenomena; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
D004986:Ether; D002734:Chlorophyll