Photophysical Properties of the Excited States of Bacteriochlorophyll <i>f</i> in Solvents and in Chlorosomes

Abstract

Bacteriochlorophyll <i>f</i> (BChl <i>f</i>) is a photosynthetic pigment predicted nearly 40 years ago as a fourth potential member of the <i>Chlorobium</i> chlorophyll family (BChl <i>c</i>, <i>d</i>, and <i>e</i>). However, this pigment still has not been found in a naturally occurring organism. BChl <i>c</i>, <i>d</i>, and <i>e</i> are utilized by anoxygenic green photosynthetic bacteria for assembly of chlorosomeslarge light-harvesting complexes that allow those organisms to survive in habitats with extremely low light intensities. Recently, using genetic methods on two different strains of Chlorobaculum limnaeum that naturally produce BChl <i>e</i>, two research groups produced mutants that synthesize BChl <i>f</i> and assemble it into chlorosomes. In this study, we present detailed investigations on spectral and dynamic characteristics of singlet excited and triplet states of BChl <i>f</i> with the application of ultrafast time-resolved absorption and fluorescence spectroscopies. The studies were performed on isolated BChl <i>f</i> in various solvents, at different temperatures, and on BChl <i>f</i>-containing chlorosomes in order to uncover any unusual or unfavorable properties that stand behind the lack of appearance of this pigment in natural environments