DFT studies of a novel phenothiazine-based fluorescent probe (PFP) for its physiochemical and thermodynamic properties

Herein, DFT studies were carried out of a novel Phenothiazine-based Fluorescent Probe (PFP) for its physio-chemical and thermodynamic properties. Various aspects were investigated including optimized geometry, frontier molecular orbitals, molecular electrostatic potential, density of states, UV-Vis emission spectra and reactivity parameters. DFT studies reveal that molecular modeling, including the optimization of molecular structures like PFP, is crucial for understanding complex molecules and their characteristics. The energy difference (∆E) between the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) was determined to be 4.48 eV. MEP maps indicate the nitrogen and sulfur atoms in the thiazine ring appear red, indicating high electron density. Similarly, the benzene rings appear blue thereby indicating lower electron density. The DOS spectrum confirmed the HOMO-LUMO gap and provided insights into the availability of electronic states at specific energy levels. High DOS intensity indicated many accessible states, while zero intensity indicated none. Time-Dependent Density Functional Theory (TD-DFT) calculations predicted the absorption maximum at 365 nm and emission spectra for PFP, with a calculated maximum emission at 656 nm. Coordination with water shifts the emission to 690 nm, showing a redshift of 44 nm. Moreover, the theoretically calculated maximum emission of probe PFP was determined to be λ em = 656 nm, whereas maximum emission spectra of probe PFP with water coordination is calculated as λ em = 690 nm which is red shifted 44 nm. These theoretically calculated values significantly deviate from experimental value. This deviation occured because the absorption and emission spectra recorded in solvents of different polarity result in different wavenumbers and intensities. Graphical abstract