Theoretical investigation of organic-inorganic hybrid crystal: Optical transparency and quadratic harmonic coefficients of 2-Amino-5-Nitropyridinium chloride

Abstract

The IR and UV absorption cut-offs ( ${\mathit{\lambda }}_{\mathit{I}\mathit{R}}$ and ${\mathit{\lambda }}_{\mathit{U}\mathit{V}}$ ) of an organic-inorganic hybrid nonlinear optical (NLO) crystal, 2-amino-5-nitropyridinium chloride (2A5NPCl), were investigated in the framework of density functional theory. The macroscopic quadratic NLO coefficients of the crystal were evaluated at the MP2/6-31+G** level coupled with the oriented-gas model. The calculated results reveal that the ${\mathit{\lambda }}_{\mathit{I}\mathit{R}}$ and ${\mathit{\lambda }}_{\mathit{U}\mathit{V}}$ are governed by the asymmetric N–H stretch of ${\mathrm{NH}}_2$ group and the charge transfer (CT) transition from ${\mathrm{Cl}}^{-}$ to 2A5NP⁺, respectively. The optical transparency has been determined in the region 407–1415 nm. The analyses of the electronic absorption spectrum show that the CTs of both Cl⁻ → 2A5NP⁺ and $\mathit{\pi }\to {\mathit{p}}^{\ast }$ within 2A5NP⁺ moiety make dominant contributions to the β values. The studies of the oriented-gas model show that the crystal has large NLO coefficients.