The inclusion of acridinedione dyes (ADR) with β-cyclodextrins (β-CD) in the presence of 0.6% methanol is studied using absorption and fluorescence techniques. The association constant was determined by using the Benesi−Hildebrand plot and also by nonlinear regression analysis. A stoichiometry of 1:1 was found for β-CD/ADR (3 − 5). The nonobservation of the changes in the absorption or the fluorescence in the case of dyes 1 and 2 clearly indicates that the phenyl substituent at the −N atom in the ADR (3 − 5) is included in the β-CD cavity. Thermodynamic parameters ΔH and ΔS values obtained from the temperature-dependent binding constants of the β-CD/ADR (3 − 5) system are reported. In the presence of β-CD, the fluorescence of ADR (4) dye shows single exponential decay, consistent with the completion of complex formation, and ADR (3, 5) showed a double exponential decay, consistent with the equilibrium between free and complexed forms. The binding constants and thermodynamic factors are systematically resolved through lifetime analysis.

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Time-dependent reorientations of resorcinol-based acridinidione (ADR) dyes in glycerol were studied using steady-state and time-resolved fluorescence studies. The difference between fluorescence anisotropy decays recorded at 460 nm when exciting at 250 nm and those obtained when exciting at 394 nm are reported. When exciting at 394 nm, the fluorescence anisotropy decay is bi-exponential, while on exciting at 250 nm a mono-exponential fluorescence anisotropy decay is observed. We interpret this in terms of different directions of the absorption dipole at 394 and 250 nm with the emission dipole respectively, which is experimentally validated and further analysed as a prolate model of ellipsoid.