SHIFTS OF THE (1)A(G)(-)-]B-1(U)+ ELECTRONIC ABSORPTION OF CAROTENOIDS IN NONPOLAR AND POLAR-SOLVENTS

The B-1(u)+ energy of carotenoids (spheroidene, neurosporene, and beta carotene) exhibits a linear dependence on R(n) =(n(2) - 1)/(n(2) + 2) in both nonpolar and polar solvents: The B-1(u)+ energy is more stabilized in polar solvents in the limit of R(n)-->0, and the line for polar solvents has a gentler slope. [As a result, the line for polar solvents crosses the line for nonpolar solvents at R(n)similar or equal to 0.3.] A theory has been developed, which explains the aforementioned observations as follows. In polar solvents, an electric field is generated by fluctuation of the solvent permanent dipoles, and it affects the rodlike, conjugated chain of the carotenoid in a long spheroidal cavity. The electric field stabilizes the B-1(u)+ energy through the polarization effect and it substantially reduces the dispersive interaction. The higher transition multipoles, rather than the transition dipole of carotenoid, play major roles in the aforementioned interactions between the carotenoid and the solvent molecules.