Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

Abstract

Ten naturally occurring chlorophylls (a, b, c (2), d) and bacteriochlorophylls (a, b, c, d, e, g) were purified and studied using the optical spectroscopic techniques of both steady state and time-resolved absorption and fluorescence. The studies were carried out at room temperature in nucleophilic solvents in which the central Mg is hexacoordinated. The comprehensive studies of singlet excited state lifetimes show a clear dependency on the structural features of the macrocycle and terminal substituents. The wide-ranging studies of triplet state lifetime demonstrate the existence of an energy gap law for these molecules. The knowledge of the dynamics and the energies of the triplet state that were obtained in other studies allowed us to construct an energy gap law expression that can be used to estimate the triplet state energies of any (B)chlorophyll molecule from its triplet lifetime obtained in a liquid environment.

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

“…These values are larger than those calculated from the spectral densities with the standard prefactor [65] in our previous paper [22]. Our MD/TDDFT calculations imply that the reorganization energies of the BChl d in the roll is larger than that in solvent (69 cm −1 ) [66]. This large reorganization energy can be a signature of a fast energy relaxation within Q y exciton states in the roll.…”

Evidence for a cysteine-mediated mechanism of excitation energy regulation in a photosynthetic antenna complex

“…TRF measurements were carried out using the laser system and universal streak camera setup described in detail previously (52), exciting at 602 nm. The spectra were cleared from noise and globally fit using the program ASUfit (13).…”

“…In oxidizing conditions, the fast lifetime of the quenching pathway (60 ps) is thought to compete with the rate of energy transfer to the RC. This pathway effectively disappears in reducing conditions, allowing the pigments to fluoresce with lifetimes similar to that of monomeric BChl a (2 ns) (13). It was suggested that the quenching effect might be controlled by a modified aromatic amino acid (e.g., tyrosylquinone or trytophylquinone) that plays a role similar to that of the excitation-quenching quinones found in the chlorosome (12).…”

Electronic and vibrational properties of carotenoids: from in vitro to in vivo

“…As light harvesters, carotenoids transfer the absorbed excited state energy to (bacterio)chlorophylls ((B)Chl); this excitation energy is eventually trapped by a reaction centre pigment -protein complex and converted into an electrical potential [19,20]. They also act as protective molecules against the photobleaching of photosynthetic organisms by quenching (B)Chl triplet states [21,22], which prevents the (B)Chlsensitized formation of singlet state oxygen [23][24][25][26][27][28][29], by scavenging singlet oxygen directly [8,30] or by quenching (B)Chl singlet states [31 -33]. Carotenoids have also been reported to stabilize protein structures, because many photosynthetic pigment -protein complexes do not fold properly without these molecules [34 -36].…”