Synthesis, photophysical properties, and density functional theory studies of phenothiazine festooned vinylcyclohexenyl‐malononitrile

A novel phenothiazine derivative conjugated with vinylcyclohexenyl‐malononitrile (PTZ‐CDN) was synthesized through the Knoevenagel reaction of 10‐octyl‐10 H ‐phenothiazine‐3,7‐dicarbaldehyde with 2‐(3,5,5‐trimethylcyclohex‐2‐en‐1‐ylidene)‐malononitrile and fully characterized. The UV–vis absorption spectra of PTZ‐CDN in different solvents showed a λ max band at 497–531 nm with a high molar extinction coefficient attributed to intramolecular charge transfer (ICT) with the characteristics of a π–π* transition. Increasing the solvent polarity resulted in a bathochromic shift of λ max . The PTZ‐CDN fluorescence emission spectra were more sensitive to increasing the solvent polarity than the absorption spectra; they displayed a blue shift of λ em by 85 nm. To understand the behaviour of the PTZ‐CDN derivative, Stokes' shift ( Δ ν ¯ ) with respect to the solvent polarity, Lippert–Mataga and linear solvation–energy relationship (LSER) models were applied in which the LSER showed better regression than the Lippert–Mataga plots ( r 2 = 0.9627). Finally, the TD‐density functional theory (DFT) electronic transition spectra in dioxane and dimethyl formamide (DMF) were calculated. The DFT data showed that λ max resulted from the support of the highest occupied molecular orbital to the lowest unoccupied molecular orbital transition with 74% and 99% in dioxane and DMF, respectively.