Non-linear optical properties of 2,7-naphthyridine derivatives for optical switching applications: a DFT study

A series of hitherto unreported naphthyridine push-pull chromophores for non-linear optical (NLO) applications including optical switching are reported. NLO parameters of these compounds have been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Compared to the parent naphthyridine, these compounds showed smaller values for the energy gap and higher values for non-linear optical parameters. In the gas phase, the dynamic hyperpolarizability values for the electro-optic Pockels effect and second harmonic generation at dispersion frequencies of 1064 nm and 1907 nm were more than the static value. From the simulated absorption spectra, the peak absorption wavelength was red shifted with the extended substitution and natural transition orbital analysis yields the percentage contribution of the dominant orbital pair transition from ground to excited state of all the studied compounds. After analyzing the solvent effects in both polar and non-polar mode, the frontier molecular orbital (FMO) energy gap and hyperpolarizability can be effectively tuned which could lead to remarkable implications for organic NLO applications. Density functional theory calculations are also applied to the naphthyridine derivatives to acquire the dipolar or octupolar contribution to first order hyperpolarizabilities. The dispersion and solvent effect studies divulged the enhancement in dipolar or octupolar contribution and hyper Rayleigh scattering (HRS) hyperpolarizabilities (beta HRS). A series of novel 2,7-naphthyridine derivatives were designed with potential applications in optical switching. The electronic properties and nonlinear optical properties of the designed compounds were extensively studied using DFT.