NONPHOTOCHEMICAL HOLE BURNING OF THE B800-B850 ANTENNA COMPLEX OF RHODOPSEUDOMONAS-ACIDOPHILA

Detailed burn wavelength-dependent hole-burning studies of the title complex have been performed. The zero-phonon hole (ZPH) widths for B800 at 4.2 K are 6.0 +/- 0.3 cm-1 and are discussed in terms of B800-B850 and B800-B800 energy transfer. The B800* lifetime is 1.8 +/- 0.2 ps. The site inhomogeneous broadening (GAMMA(I)) of B800 is 240 cm-1. The B850 (located at 864 nm at 4.2 K) hole spectra reveal that B850 suffers from significant homogeneous broadening, which is attributed to unit cell exciton level structure and ultrafast interexciton level relaxation. Novel ZPH action spectra lead to the resolution of a minor component at 885 nm, which is the analogue of B870 of Rhodobacter sphaeroides previously assigned as the lowest exciton level of the B850 exciton band. The B870 ZPH width of 2.0 +/- 0.2 cm-1 for Rhodopseudomonas acidophila leads to a total dephasing time of 5.3 ps, which is attributed to exciton scattering that stems from the energetic inequivalence of neighboring B850 unit cells.