title: Fluorescence lifetimes of dimers and higher oligomers of bacteriochlorophyll c from Chlorobium limicola.
abstract: Fluorescence lifetimes have been measured for bacteriochlorophyll (BChl) c isolated from Chlorobium limicola in different states of aggregation in non-polar solvents. Two different homologs of BChl c were used, one with an isobutyl group at the 4 position, the other with n-propyl. Species previously identified as dimers (Olson and Pedersen 1990, Photosynth Res, this issue) decayed with lifetimes of 0.64 ns for the isobutyl homolog, 0.71 ns for n-propyl. Decay-associated spectra indicate that the absorption spectrum of the isobutyl dimer is slightly red-shifted from that of the n-propyl dimer. Aggregates absorbing maximally at 710 nm fluoresced with a principal lifetime of 3.1 ns, independent of the homolog used. In CCl4, only the isobutyl homolog forms a 747-nm absorbing oligomer spectrally similar to BChl c in vivo. This oligomer shows non-exponential fluorescence decay with lifetimes of 67 and 19 ps. Because the two components show different excitation spectra, the higher oligomer is probably a mixture of more than one species, both of which absorb at ∼747 nm.
authors.affiliation: Department of Chemistry, Arizona State University, 85287-1604, Tempe, AZ, USA.
authors.forename: T P
authors.initials: TP
authors.lastname: Causgrove
authors.forename: D C
authors.initials: DC
authors.lastname: Brune
authors.forename: R E
authors.initials: RE
authors.lastname: Blankenship
authors.forename: J M
authors.initials: JM
authors.lastname: Olson