ИСТИНА

Isotropic and anisotropic pump-probe spectra of Cf.aurantiacus chlorosomes were measured on the fs- through ps-time scales for the B798 BChl a Qy band upon direct excitation of the band at T = 293K and T = 90K. The shape of the BChl a spectra was shown to be independent of the size of the whole chlorosomal antenna. The monomeric nature of BChl a was manifested. The anisotropy parameter value r was constant within the BChl a band at both temperatures and decayed from r = 0.4 (at 200 fs delay time) to r = 0.10 at T=293K or to r = 0.09 at T=90K (at 30÷100 ps delay time). The anisotropy decay exhibited a fast component, reflecting the decay of coherences between the one-exciton B798 states that is followed by ps-depolarization due to B798→B798 localized exciton migration. The theoretical dependence of the steady state anisotropy parameter r on the angle Ө was presented for the model, in which the BChl a Qy transition dipoles randomly distributed around the normal to the baseplate plane form the angle Ө with the normal. According to the theoretical dependence r(Ө), the angle Ө corresponding to the experimental steady state value r = 0.1 at T = 293K was found to equal 35.3°. As the temperature drops to 90K the angle Ө insignificantly increases.