Experimental and theoretical studies on solvent effects of amphiphilic conjugated polyenals

The spectroscopic properties of amphiphilic pi-conjugated omega,omega'-(alkoxyphenyl)polyenals (alkoxy = methoxy, hexyloxy) containing from 1 to 8 double bonds have been studied both experimentally and theoretically. The studies considered the solvent effects on the spectral position and profiles of the absorption according to a great role of the solvent in photochemical processes. Positive solvatochromism in nonpolar solvents (2,2,4-trimethylpentane, CCl4, tetrahydrofuran, CH2Cl2) and negative solvatochromism in polar solvents (C2H5OH, CH3OH, CH3CN and dimethysulfoxide) suggest that an increase of solvent polarity causes a change of the canonical polyene structure-shift from a more polymethine-like to a more polyene-like state. Experimental findings were supported by theoretical calculations performed by AM1-CI/SM5.4/A method implemented in the AMSOL package from which dipole moments and free energy of solvation in ground mu(gs), DeltaG(s)(gs) and excited mu(ex), DeltaG(s)(ex) state, respectively, proved that the continuum model of the solvent is satisfactory only for non-polar systems because in the polar solvents the specific solvent-solute interactions may introduce noticeably discrepancies in the solvation parameters. This theoretical method appeared useful to predict the critical parameter for the molecular admittance-HOMO-LUMO band gap-for conjugated polyenals in solvents of various polarity.