A comprehensive study on the effect of substitution position and solvent effect on absorption and emission characteristics of n-methylindoles via linear response and State-Specific formalisms

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 450; p. 115469
• Main Authors: Karaca, Caglar, Bardak, Fehmi, Kose, Etem, Atac, Ahmet
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2024
• Subjects: Emission; Franck-Condon analysis; Linear response; N-methylindole; Solvatochromic shifts; State specific; N-methylindole; Emission; Solvatochromic shifts; Linear response; Franck-Condon analysis; State specific
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2024.115469

[Display omitted] •Absorption-emission characteristics of n-methylindoles in solvents were obtained.•The electronic properties were obtained at DFT/TD-DFT CAM-B3LYP-6-311++G(d,p) level.•The solvatochromic effects were investigated through LR and SS approaches.•The effect of methyl position on the electronic transition characteristics was outlined.•SS solutions give greater accuracy than LR for the solvatochromic effects for higher polarities. The light absorption emission characteristics of n-methylindoles (n = 1–7) have been explored thoroughly by taking solvatochromic, substitution position, and solvation model effects into account. Experimental UV–Vis and Fluorescence spectra were recorded between 200 and 400 nm, and 250–800 nm, respectively, in cyclohexane, dichloromethane, and acetonitrile. Molecular geometry optimizations and excited state calculations were conducted using DFT and TD-DFT methods with a long-range corrected hybrid exchange–correlation functional CAM-B3LYP. Absorption emission characteristics were determined based on the polarizable continuum model accompanied with Linear-Response and State-Specific formalisms. Absorption spectra were resolved using Franck-Condon analysis for a more accurate representation of experimental data and underlying vibronic transitions were determined. Overall, although the Linear-Response and State-Specific approaches provide a quantitative explanation of experimental spectra, the approach used for the calculations can affect the solvent polarity-dependent shifts by nearly an order of magnitude. Besides, the State-Specific model provides slightly better results in the determination of Stokes shifts. The shouldered fluorescence peak observed in weakly polar solvents diminishes at higher polarities indicating the elimination of solute–solute interactions and domination of solute–solvent interactions with increasing solvent polarity.