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

• Published in: Luminescence (Chichester, England) England), 2020-11, Vol.35 (7), p.998-1009
• Main Authors: Al‐Zahrani, Fatimah A.M., Alzahrani, Khalid Ahmed, El‐Shishtawy, Reda M., Abu Mellah, Khloud, Al‐Soliemy, Amerah M., Asiri, Abdullah M.
• Format: Article
• Language: English
• Subjects: Absorption; Absorption spectra; Blue shift; Charge transfer; Density functional theory; DFT studies; Dimethylformamide; Emission spectra; energy gap; Extinction coefficient; Fluorescence; Malononitrile; Molecular orbitals; Phenothiazine; Polarity; Solvation; solvatochromism; Solvents; Spectra
• ISSN: 1522-7235; 1522-7243
• DOI: 10.1002/bio.3804

A novel phenothiazine derivative conjugated with vinylcyclohexenyl‐malononitrile (PTZ‐CDN) was synthesized through the Knoevenagel reaction of 10‐octyl‐10H‐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 λmax 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 λmax. The PTZ‐CDN fluorescence emission spectra were more sensitive to increasing the solvent polarity than the absorption spectra; they displayed a blue shift of λem by 85 nm. To understand the behaviour of the PTZ‐CDN derivative, Stokes' shift ( Δν¯) 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 (r2 = 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 λmax 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.