Red Emitting Hydroxybenzazole (HBX) Based Azo Dyes: Linear and Non Linear Optical Properties, Optical Limiting, Z Scan Analysis with DFT Assessments.

Herein, we report the hydroxybenzazole (HBX) containing azo dyes for "linear and non-linear optical" (NLO) applications. These bi-heterocyclic dyes have HBX scaffold (decorated with ESIPT core) and connected to another thiazole moietiy through azo bond. In DMF and DMSO, dyes are "emissive in yellow-red region" and "large Stokes shift" in the range of 62-121 nm were observed. "Nonlinear absorptive coefficient" (β), "nonlinear refractive index" (ƞ2), "third order non-linear optical susceptibility" (χ3) in DMSO, ethanol and methanol were calculated using simple and effective "Z-scan technique" having "Nd: YAG laser" at 532 nm wavelength. 4.46 × 10-13 (e.s.u.) was the highest (χ3) was observed in DMSO among all the dyes. Optical Limiting (OL) values are in the range of 7.61-19.06 J cm-2 in solvents. Thermo Gravimetric Analysis (TGA) supports that, these compounds are useful for numerous high-temperature practices in the construction of electronic as well as optical devices. Band gap was calculated by CV as well as by DFT in acetonitrile. The same trend was observed when these HOMO-LUMO gaps were correlated in between CV and DFT. To gain more insights into structural parameters, molecular geometries were optimized at "B3LYP-6-311 + G (d,p)" level of theory. Further, "Molecular Electrostatic Potential" (MEP), "Frontier Molecular Orbitals" (FMO) were presented using "Density Functional Theory (DFT)". Global hybrid functional (B3LYP, BHandHLYP) and range separated hybrid functionals (RSH) i.e. CAM-B3LYP, ωB97, ωB97X, and ωB97XD were used to calculate linear and NLO properties. Graphical Abstract.