Comparative study of the energy transfer kinetics in artificial BChl e aggregates containing a BChl a acceptor and BChl e-containing chlorosomes of Chlorobium phaeobacteroides.

Chlorosomes are the light-harvesting organelles of green bacteria, containing mainly special bacteriochlorophylls (BChls) carrying a 3(1)-hydroxy side chain. Artificial aggregates of BChl c, d, and e have been shown to resemble the native chlorosomes in many respects. They are therefore seen as good model systems for understanding the spectroscopic properties of these antenna systems. We have investigated the excitation energy transfer in artificial aggregates of BChl e, containing small amounts of BChl a as an energy acceptor, using steady-state and time-resolved fluorescence. Global analysis of the kinetic data yields two lifetimes attributable to energy transfer: a fast one of 12-20 ps and a slower one of approximately 50 ps. For comparison, BChl e-containing native chlorosomes of Chlorobium phaeobacteroides and chlorosomes in which the energy acceptor had been degraded by alkaline treatment were also studied. A similar behavior is seen in both the artificial and the natural systems. The results suggest that the artificial aggregates of BChls have a potential as antenna systems in future artificial photonic devices.