Preparation and photophysical properties of benzimidazole-based gels

Two kinds of benzimidazole-based compounds, pyridinium salts (1a–3b) and amides (4a, 4b), which consist of long alkyl chains and benzimidazole moiety, were designed as blue colour fluorescent gelators. The pyridinium salts 1a–3b were synthesized using the simple and economical microwave-assisted method. The gelation ability of 1a–2b in a variety of organic solvents was higher than that of 3a–4b. The SEM of the gels showed fibrous, spherical and filmlike morphologies depending on the gelators and the solvents. Red shift of fluorescence spectra and blue shift of absorption spectra from solution to gel state was observed in the organic solvent tested. The fluorescence intensity of the gel and the solution state increased with the increase of the solvent polarity. The fluorescence quantum yields of the gels were found to be considerably lower by one or two orders of magnitude than those of the solutions.