SOLVENT EFFECT ON SPHEROIDENE IN NONPOLAR AND POLAR SOLUTIONS AND THE ENVIRONMENT OF SPHEROIDENE IN THE LIGHT‐HARVESTING COMPLEXES OFRhodobacter sphaeroides2.4.1 AS REVEALED BY THE ENERGY OF THE1Ag−→1Bu+ABSORPTION AND THE FREQUENCIES OF THE VIBRONICALLY COUPLED C=C STRETCHING RAMAN LINES IN THE1Ag−AND1Bu−STATES

Abstract

Abstract–The1Ag−→1Bu+electronic absorption band and the vibronically coupled, C=C stretching Raman lines in the1Ag−and 21Ag−states were recorded for spheroidene free in nonpolar and polar solvents as well as for spheroidene bound to the LH1 and LH2 complexes ofRhodobacter sphaeroides2.4.1. The1Bu+energy exhibited a linear dependence on R(n) = (n2‐ 1)/(n2+ 2) in both nonpolar and polar solvents; the line for polar solvents had a gentler slope and crossed the line for nonpolar solvents at R(n) = 0.3. The above characteristic of polar solvents was ascribed to the electric field generated by fluctuation of the solvent permanent dipoles; it stabilizes the1Bu+energy and reduces the polarizability of the solvent. The vibronically coupled, C=C stretching frequencies in the1Ag−and 21Ag−states [ν(Ag) and [ν(2Ag)] also showed similar dependence on R(n), which is explained in terms of vibronic coupling among the1Ag−, 21Ag−and 31Ag−states.The environment of spheroidene in the LH2 and LH1 complexes was assessed on the basis of the1Bu+energy and the ν(Ag) and [ν(2Ag) frequencies: Spheroidene in the LH2 complex is located in an environment with high polarizability, while spheroidene in the LH1 complex is located in an environment with lower polarizability.