Fluorescence-detected triplet kinetics study of the specifically solvated chlorophyll a and protochlorophyll in frozen solutions

✍ Scribed by K. Mauring; I. Renge; P. Sarv; R. Avarmaa

• Publisher: Elsevier Science
• Year: 1987
• Tongue: English
• Weight: 540 KB
• Volume: 43
• Category: Article
• ISSN: 1386-1425
• DOI: 10.1016/0584-8539(87)80052-1

✦ Synopsis

The triplet lifetimes (T 7) of the title compounds have been measured in a number of solvent hosts by using an indirect triplet state detection through fluorescence fading kinetics at 77 K. Three types of complexes with solvent molecules, i.e. with a mono-(Lt-type) and bisligated (L2-type) central magnesium atom and the latter with hydrogen bridges (L2 H-type), have average zrvalues of 2.5, 1.4 and 0.8 ms and 10, 4.5 and 2.5 ms for chlorophyll a (Chl a) and protochlorophyll (PChl), respectively. Hydrogen-bor.ded Lt H-type complexes of Chl a occurring in tert-alcohols and perfluoroaniline have the same z r as L t-type solvates. The solvent deuteration isotopic effects show that in L2 H-complexes (e.g. in methanol) triplet quenching arises partially due to electronic energy transfer to the vibrational overtones of OH groups attached via Mg atom to the central part of Chl a macrocycle. The dependence of fluorescence band-shapes and maxima on the excitation wavelength indicates the presence of several types of pigment-solvent complexes in most matrices. Minor amounts ( ~ 1%) of L 2-and L 2 H-type solvates on the background of dominating monoligated species could be selectively excited with a 457.9 nm Ar ÷ laser line.