Fluorescence and β-cyclodextrin inclusion properties of three carbazole-based dyes

Fluorescence behavior of three carbazole-based dyes, 2-(9H-carbazol-9-yl) butanoic acid, 2-(1,4-dimethyl-9H-carbazol-9-yl)acetic acid and 3-(1,4-dimethyl-9H-carbazol-9-yl)propanoic acid were examined. General solvent effects of the butanoic and acetic acid derivatives in 23 different solvents was not well-described by the Lippert–Mataga equation, indicating a specific solvent effect due to intermolecular hydrogen bonding dominated fluorescence spectra. The emission wavelengths and fluorescence intensities were relatively stable in aqueous acetonitrile and aqueous methanol solutions. Their fluorescence intensities increased from low to high pH and also from high to low temperature. The acid dissociation constants of the three carbazole derivatives in their ground state were estimated to be in the range 3.2–4.8. The fluorescence intensities were also enhanced in the presence of β-cyclodextrin. The average stability constant of the inclusion complexes was 21.2 ± 13.4 at pH3 and 54.0 ± 7.0 at pH8. A molecular dynamics simulation indicated that the carbazole moiety was partially included into the β-cyclodextrin cavity leaving the carboxylic acid group exposed.

► Specific solvent effect due to intermolecular hydrogen bonding dominated fluorescence spectra.
► Emission wavelength and fluorescence intensity stable in aqueous acetonitrile and aqueous methanol.
► Fluorescence intensity increases on change from low to high pH but decreases upon increasing temperature.
► The fluorescence intensity enhanced in β-CD presence with weak binding.
► Molecular dynamics simulation indicates that the carbazole moiety is partially included into β-CD cavity.