VIBRATIONALLY EXCITED-STATES IN CAROTENOIDS - PICOSECOND TIME-RESOLVED ANTI-STOKES RESONANCE RAMAN-SPECTROSCOPY

Transient vibrationally excited, ground-state populations of carotenoids have been observed for in vivo pigment-protein complexes of Chromatium vinosum and in vitro samples of the isolated carotenoid spirilloxanthin in benzene solution using picosecond time-resolved anti-Stokes resonance Raman scattering. These populations are formed under the same excitation conditions recently used to detect the transient populations of the ground 1A(g) and excited 2 1A(g) and 3B(u) electronic states in the same molecular systems. The time-dependent anti-Stokes resonance Raman band intensities show that these populations decay via vibrational relaxation within 50 ps. These data experimentally confirm an excited state relaxation mechanism postulated to describe the population dynamics among the 1A(g), 1B(u), 2 1A(g), and 3B(u) electronic states in both in vivo and in vitro carotenoids.