Synthesis, spectroscopic properties, and DFT correlative studies of 3,3′- carbonyl biscoumarin derivatives

Abstract

• Photophysical properties of probes Bis-Coumarin derivatives have been investigated. • The probes are more polar in the excited state than the ground state. • HOMO-LUMO & Optical energy band gaps are in agreement with each other. • Chemical hardness studies suggest soft nature for the probes. • MESP plots exhibit both electrophilic & nucleophilic sites. A facile and simple method for the synthesis of a library of 3,3′- Carbonyl biscoumarin derivatives via a one-pot chemical reaction is reported. The synthesized fluorescent dyes were purified and characterized by analytical methods. The IR, 1 H-NMR, and MS results confirmed the corresponding structure of the fluorescent dyes. The absorption and fluorescence spectra of fluorescent dyes were recorded in different solvents of varying polarity to understand the solvatochromic behaviour and dipole moments. Stoke's shift exhibits a redshift with an increase in solvent polarity for all molecules indicating a π→π ∗ transition. The ground state dipole moments of all fluorescent dyes are estimated theoretically from ab initio computations (integral equation formalism of polarizable continuum model) and experimentally from the solvatochromic method and the results are compared. Further, using solvatochromic correlations like Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's, and solvent polarity parameter the excited state dipole moments are determined. Results show that the excited state dipole moments are higher than the ground state dipole moments which suggests that, all fluorescent dyes are more polar in the excited state. The HOMO-LUMO energy gaps computed from density functional theory and absorption threshold wavelengths are found to be in good agreement and also support intramolecular charge transfer (ICT). Using HOMO-LUMO energies, the chemical hardness (η) of the molecules is determined and the chemical stability is discussed. Further, using DFT molecular electrostatic potential (MESP) plots, the electrophilic site and nucleophilic site which are useful in photochemical reactions were identified. The preliminary observations and results suggest that the fluorescent dyes can be considered as potential candidates for fluorescent probes and construction of dye-sensitized solar cell in future