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 1Bu+→1Bu−→2Ag− internal conversion, whereas the latter experiment identified a transformation of 1Bu+→2Ag−→T1(13Bu+). Excitation to the 1Bu+(0) or 1Bu+(1) vibronic level resulted in enhancement of stimulated emission from the particular level, showing that vibrational relaxation in the 1Bu+ state has a time constant comparable to, or larger than, that of electronic relaxation.