Spectroscopic and Theoretical Insights on Azulene-<i>p</i>-chloranil Charge Transfer Interaction in Solution

Azulene (A) interacted spontaneously with [Formula: see text]-chloranil (P) in toluene. Charge transfer (CT) absorption band for the A-P system was located at 528.9 nm. Utilizing the CT absorption maximum ([Formula: see text], several important physicochemical parameters were evaluated in this study. The average value of the binding constant of the A-P system was estimated to be (3.67 ± 0.25) × 10 4 dm 3 ⋅ mol[Formula: see text]. The strong interaction between A and P was well supported by proton NMR and fluorescence microscopy results. Quantum chemical calculations performed by the DFT/B3LYP, DFT/B3LYP/D3 and DFT/M06-2X methods in both gas phase and in non-polar solvent established the complexation between A and P in solution. Time-dependent density functional theoretical calculations employing M06 method in both gas phase and in solution generated the [Formula: see text] value of 536.0 nm and 527.9 nm, respectively, which corroborates excellently well with the result obtained from UV–Vis experiments.