Structural and photophysical properties of alkylamino substituted 2-arylidene and 2,5-diarylidene cyclopentanone dyes

• A set of alkylamino substituted 2-arylidene and 2,5-diarylidene cyclopentanones have been synthesized and characterized.
• The spectroscopic and photophysical properties of these compounds have been measured in solvents of various polarity.
• The spectroscopic and photophysical properties of these compounds exhibited solvent dependence.
• These compounds have been shown to exhibit solvatochromic and photoinduced internal charge transfer properties.
• A few of the compounds have been shown to undergo excited state protonation when dissolved in glacial acetic acid.

A series of alkylamino substituted 2-arylidene and 2,5-diarylidene cyclopentanone compounds were synthesized. Spectroscopic and photophysical properties of these compounds have been measured in a variety of solvents. Absorption and fluorescence maxima have been correlated with the Empirical Scale of Solvent Polarity (ET(30)). Theoretical TD-DFT spectral calculations and Lippert–Mataga analysis support the internal charge transfer (ICT) nature of the S0 → S1 excitation for these compounds, with higher degrees of ICT depicted for the alkylamino substituted 2,5-diarylidene cyclopentanones. Photophysical properties consisted of measuring the fluorescence quantum yields (Φf) and lifetimes (τf) in a variety of solvents. Radiative and nonradiative decay constants have been determined from the Φf and τf data. Variation with solvent in the nonradiative rate of decay is interpreted in terms of a competition between internal conversion and intersystem crossing. Lastly, two compounds presented have been shown to undergo excited state protonation in glacial acetic acid.