Synthesis, characterization and solvent effects on the electronic properties and non-linear optical activity of acridine-1,8-diones-proline based fluorescent probe for visual recognition and selective detection of OH- ion

Design of optical probes for the visual detection and quantification of hydroxide ions in a highly alkaline solution remains a challenge. Here we present the synthesis and photophysical behaviour of a new fluorescent probe (Cmpd-5) intended for hydroxide ion sensing. The UV-vis absorption and fluorescence spectra of Cmpd-5 were studied in a variety of solvents of different polarity. The decay analysis indicated the fast-radiative decay of the probe in all solvents. Further, Cmpd-5 was found to be effective for naked-eye detection of hydroxide ions in the semi aqueous conditions with great sensitivity and selectivity. The transient photoluminescence decay analysis indicated that the average lifetime of Cmpd-5 was increased 2.5 times upon the addition of OH-. To ascertain the electronic features of the compound, density functional theory (DFT) computations were used employing the M06-2X/def2-TZVP level of theory. Molecular electrostatic potential maps were used to identify reactive sites of the molecule in different solvents. We examined the impact of various solvents on Frontier Molecular Orbitals (FMOs), global and local reactivity descriptors. The UV-visible spectra were analyzed using the time-dependent density functional theory (TDDFT) method, and the results of the experiments and the calculated values show reasonable consistency. Theoretical NLO (nonlinear optical) investigations in various solvents revealed that the compound had a greater NLO activity in all solvents than the standard molecule urea. Moreover, non-covalent interactions (NCI) were investigated to assess van der Waals interactions.