DISPERSIVE INTERACTION OF NON-POLAR SOLUTES WITH NON-POLAR SOLVENTS - SOLVENT EFFECTS ON ELECTRONIC SPECTRA OF CAROTENOIDS

From the known model for the dispersive interaction of a non-polar solute with a non-polar solvent the following predictions can be derived for the behaviour of the electronic spectrum of a polyene dissolved in binary mixed solvents: (a) With increasing concentration of the more strongly interacting solvent component the 1A → 1Bo transition is shifted toward longer wavelengths (b) This bathochromic shift is accompanied by a decrease of the oscillator strength fM of the 1A → 1Bo transition, (c) Both Δ v and the relative oscillator strength f′M/fM, are linear functions of the more concentration of the more strongly interacting solvent component expressed in volume per cent. (d) Both Δ v and f′M/fM, are in a first approximation independent of the number of conjugated double bonds of the polyene. Thesame predictions can be derived from a theoretical model due to Liptay which includes second order effects. These predictions have been verified using as model systems solutions of carotenoids (with 5 to 15 conjugated double bonds) in mixtures of hexane/carbon disulfide or cyclohexane/carbon disulfide. © 1969.