抄録
To examine the effect of methyl groups on the optical absorption of retinal in ethanol solution, the π-electronic states of desmethyl retinals are calculated by extending our previous LCAO–ASMO–SCF–CI method to include 2pz- and pseudo π-orbitals in methyl branches of polyene chain. The effect of ethanol solvent is also taken into account in the two ways: (1) the effect is assumed to be implicitly included into the parameters of calculation; (2) the interaction of retinal with its neighboring ethanol molecule is explicitly calculated regarding ethanol as a point-dipole. It is thus shown that the observed λmax’s of desmethyl retinals with all-trans, 9-cis or 11-cis form can reasonably be explained by taking account of the change in structure due to the substitution of methyl group(s) by hydrogen atom(s).
