Novel 2H-pyran-3-carbonitrile dyes – Synthesis, solvatochromism study, and DFT, TD-DFT computations

Abstract

In this paper, we report two new 2H-pyran-3-carbonitrile derivatives having two different coumarin parental units with intramolecular charge transfer (ICT) and twisted intramolecular charge (TICT) properties. The absorption and emission spectra are studied in different organic solvents at room temperature. The dye 3b shows red shifted absorption and emission compared to the dye 3a because of the rigidized structure. 2H-pyran-3-carbonitrile derivatives exhibit strong fluorescence properties in various solvents and show positive solvatochromism. The dyes 3a and 3b show maximum fluorescence quantum yield in chloroform and tetrahydrofuran (ϕ: 0.81, 0.90). The bathochromic shift of absorption/emission spectra and increase in dipole moment after excitation of the dyes 3a and 3b indicate the intramolecular charge transfer (ICT)/Twisted intramolecular charge transfer (TICT) character of the emitting singlet state. Density functional theory (DFT) and time dependent-density functional theory (TD-DFT) computations have been used to understand the structural, molecular, electronic and photophysical parameters of the push-pull dyes. The ratio of ground to the excited state dipole moment of the synthesized dye is calculated with the help of Bakhshiev and Bilot–Kawski correlations.