Excited state properties of aryl carotenoids.
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 phi-ring, chlorobactene, beta-isorenieratene and isorenieratene, and compared them with their non-aryl counterparts gamma-carotene and beta-carotene, which contain beta-ring. Changing beta-ring to phi-ring did not reveal any changes in absorption spectra, indicating negligible effect of the phi-ring on the effective conjugation length. This observation is further supported by the carotenoid S(1) lifetimes. In n-hexane, the S(1) lifetime of chlorobactene having one phi-ring is 6.7 ps, while the S(1) lifetime of the beta-ring analog, gamma-carotene is 5.4 ps. The same effect is observed for the series beta-carotene (two beta-rings), beta-isorenieratene (one beta- and one phi-ring) and isorenieratene (two phi-rings) whose S(1) lifetimes in n-hexane are 8.2, 10.3 and 12.7 ps, respectively. The systematically longer lifetimes of aryl carotenoids show that the additional conjugated C=C bonds at the phi-ring do not contribute to the conjugation length. The S(1) lifetimes of aryl carotenoids were slightly shortened in benzene, indicating pi-pi stacking interaction between the phi-ring and benzene.
Institute of Physical Biology, University of South Bohemia, Zámek 136, Nové Hrady 37333, Czech Republic. fuciman@ufb.jcu.cz
Marcel
M
Fuciman
Pavel
P
Chábera
Anita
A
Zupcanová
Petr
P
Hríbek
Juan B
JB
Arellano
Frantisek
F
Vácha
Jakub
J
Psencík
Tomás
T
Polívka
D002338:Carotenoids / Q000737:chemistry*; D019414:Chlorobi / Q000737:chemistry; D011789:Quantum Theory; D013053:Spectrophotometry; D013997:Time Factors; D019207:beta Carotene / Q000737:chemistry
D019207:beta Carotene; C006980:chlorobactene; D002338:Carotenoids