Theory of Picosecond-Laser-Induced Fluorescence from Highly Excited Complexes with Small Numbers of Chromophores

• Published in: Biophysical journal 1986-02, Vol.49 (2), p.469-477
• Main Authors: Gülen, Demet, Wittmershaus, Bruce P., Knox, Robert S.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell structures and functions; Chloroplast, photosynthetic membrane and photosynthesis; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(86)83656-6

The problem of singlet excitation kinetics and dynamics, especially at high excitation intensities, among a small number of chromophores of a given system has been addressed. A specific scheme for the kinetics is suggested and applied to CPII, a small chlorophyll (Chl) a/b antenna complex the fluorescence lifetime of which has been reported to be independent of excitation intensity over a wide intensity range of picosecond pulses. We have modeled the kinetics from the point of view that Chl a molecules in CPII are Förster coupled so that a second excitation received by the group of Chl a's either creates a state with two localized excitons or raises the first one to a doubly excited state. The data on CPII can be understood on the basis of a kinetic model that does not exclude exciton annihilation during the excitation pulse. The implied annihilation rate is consistent with our theoretical estimates of that rate obtained by applying excitation transfer theory to pairs of molecules both initially excited.