Abstract
Excited-state properties of aryl carotenoids, important components of light harvesting antennae of green sulfur bacteria, have been studied by femtosecond transient absorption spectroscopy. To explore effects of the conjugated aryl group, we have studied a series of aryl carotenoids with conjugated f-ring, chlorobactene, b-isorenieratene and isorenieratene, and compared them with their non-aryl counterparts g-carotene and b-carotene, which contain b-ring.
Changing b-ring to f-ring did not reveal any changes in absorption spectra, indicating negligible effect of the f-ring on the effective conjugation length. This observation is further supported by the carotenoid S1 lifetimes.
In n-hexane, the S1 lifetime of chlorobactene having one f-ring is 6.7 ps, while the S1 lifetime of the b-ring analog, g-carotene is 5.4 ps.