SOLVATOCHROMIC SHIFTS OF NONDIPOLAR MOLECULES IN POLAR-SOLVENTS

Centro-symmetric molecules such as anthracene and its 9,10-disubstituted derivatives often show solvatochromic shifts of their absorption and fluorescence spectra in a series of solvents of different static dielectric constants. These shifts have been explained by the existence of small dipole moments of such molecules in excited states or by the ''solvent Stark effect'' which results from fluctuations of the electric field produced by the polar solvent. It is suggested that the origin of these solvatochromic shifts is the solute quadrupole-solvent dipole interaction which is not considered in the simple electrostatic models.