Experimental and theoretical studies on solvent effects of amphiphilic conjugated polyenals

Abstract

The spectroscopic properties of amphiphilic π-conjugated ω,ω′-(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 μ_gs, ΔG^gs_s and excited μ_ex, ΔG^ex_s 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.