Observation of Fascinating Nonlinear Optical Features of Fluorescent Dye in Selected Polar Solvents by Z-Scan and DFT...

Third-order nonlinear optical (NLO) properties of Acridine Orange (AO) dye were studied using Z-scan method under low power conditions and DFT method. The dye was completely dissolved in polar solvents, including ethanol, methanol, acetone, and 1-propanol. Significant optical nonlinearity was observed in polar liquids, with methanol showing the largest optical susceptibility for the AO dye. The open aperture (OA) Z-scan results indicate both positive and negative nonlinearities, attributed to saturable absorption (SA) and reverse saturable absorption (RSA). The closed aperture (CA) Z-scan results for the AO dye in all solvents demonstrated self-defocusing phenomena, as evidenced by a curve that displayed a peak followed by a valley in transmittance. The nonlinear absorption coefficient and nonlinear refractive index of the AO dye were measured to be the order of 10^-7cm²/W and 10^-2 cm/W, respectively. The third-order NLO susceptibility (χ³) of the AO dye was found to be the order of 10^-7 esu. The effect of solvents on the solute molecules were examined using Kamlet-Abboud-Taft multi-parameter scale, which quantified the contribution percentages of solvent spectral features. Additionally, the NLO properties of the AO dye were investigated using density functional theory (DFT) at the B3LYP/6-311 + + G(d,p) level. Analyses were performed on geometry optimization, Frontier Molecular Orbital (FMO), and Electrostatic Potential (ESP). Furthermore, linear polarizability (α), first-order hyperpolarizability (β), and second-order hyperpolarizability (γ) were computed in various solvents, revealing a solvent-dependent enhancement of NLO properties that aligns with the experimental data.