Sub-picosecond time-resolved absorption spectroscopy of all-trans-neurosporene in solution and bound to the LH2 complex from Rhodobacter sphaeroides G1C

Sub-picosecond, time-resolved absorption spectra of all-trans-neurosporene, both free in n-hexane solution and bound to the LH2 complex from Rhodobacter sphaeroides G1C, were recorded and analyzed by singular-value decomposition followed by global fitting using a sequential model. The former experiment identified the 1B(u)(+)--> 1B(u)(-) --> 2A(g)(-) internal conversion, whereas the latter experiment identified a transformation of 1B(u)(+) --> 2A(g)(-) --> T-1(l(3)B(u)(+)). Excitation to the 1B(u)(+)(0) or 1B(u)(+)(1) vibronic level resulted in enhancement of stimulated emission from the particular level. showing that vibrational relaxation in the 1B(u)(+) state has a time constant comparable to, or larger than, that of electronic relaxation. (C) 2000 Elsevier Science B.V. All rights reserved.