NLO Properties of 2‐Napthol Monoazo Disperse Dyes by DFT and Z‐Scan Technique – A Detailed Study

Abstract

The non‐linear and linear optical properties of 2‐napthol based four monoazo dyes were examined by computational and Z‐scan methods. Time‐dependent (TD)‐density functional theory (DFT) computations were used to evaluate the linear polarizability (α), first‐order hyperpolarizability (β) and second‐order hyperpolarizability (γ) using global hybrid and range separated hybrid functionals at 6–311+ G (d) basis set. The functional, ωB97 performed better in the determination of linear polarizability (α) and ωB97X−D performed better in the determination of the first‐order hyperpolarizability (β) and second‐order hyperpolarizability (γ) among the global hybrid and range separated hybrid functionals. To support our theoretical findings for α, β, and γ, we have correlated with the Hammett‐coefficient (σ), excited state coefficient (σex) as well as by hyper‐hardness (Γ) relations. Third order NLO parameters – non‐linear refractive index (η2), non‐linear absorption coefficient (β), real parts and the imaginary parts of third order susceptibility (χ(3)), and second order hyperpolarizability (γ) were investigated by close and open aperture methods using Z‐scan technique. The –NO2 substituted dye 2 shows higher value of molecular susceptibility (χ(3)), polarizability (α), and hyperpolarizability (β, γ) parameters among the studied azo dyes. They are likely to have potential applications in optoelectronics and photonics.