Photoisomerization and Fluorescence of Surfactant and Hydrophobic 4- and 4,4'-Substituted Stilbenes in Homogeneous Solution. Observation of Strong Fluorescence Enhancement by Dialkyl Substitution

Article abstract of DOI:10.1021/j100253a033

Several stilbenes substituted at one (4-) or both (4,4'-) para positions with linear alkyl chains terminating in hydrogen or carboxyl groups have been prepared.These surfactant or hydrophobic stilbenes have been studied primarily in organized assemblies; this paper reports on their behavior in homogeneous (benzene and methylcyclohexane) solution.The behavior of these stilbenes on direct irradiaton is characterized by strong increases (4-5-fold) in both fluorescence and singlet lifetimes for all of the disubstituted or "intrachain" deriatives compared to trans-stilbene; in contrast, relatively little effect is observed for the monosubstituted derivatives.Although the quantum yield for direct trans -> cis isomerization is reduced as a consequence of the enhanced fluorescence, the cis/trans excited singlet decay ratio is unaffected.Studies of the sensitized isomerization indicate that triplets of the substituted stilbenes have similar energies and cis/trans decay ratios to trans-stilbene; however, a somewhat longer triplet lifetime is indicated.The primary changes noted can be accounted for in terms of an enhanced sensitivity of the intrachain stilbenes to viscosity-torsional interactions between solute and solvent.