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 (λ$_{IR}$ and λ$_{UV})$ 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 λ$_{IR}$ and λ$_{UV}$ are governed by the asymmetric N-H stretch of NH$_{2}$ group and the charge transfer (CT) transition from 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 π → p* 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.