How much length of boron-nitride incorporated benzene like structures can produce efficient harmonic generation at their low-lying excited states?

Abstract

In this study, exploring the nonlinear optical (NLO) responses by utilizing boron nitride (BN) units as benzene like fused ring chromophores (BTN1-BTN8) are made by correlating their planarity. The chromophore structures containing ring sizes of 3 and 4 (BTN3 and BTN4) demonstrates their significant NLO responses, while higher ring sizes show a decline as their structure become more curved. Their quantum chemical calculations are performed to optimize their molecular structures for their various chemical stability related parameters. Their dipole moments (µtot) ranges between 1.27D for BTN2 to 4.43 D for BTN8 while their average linear polarizability (<α0>) varies from 5.98–7.56 electrostatic units (e.s.u). The chromophore BTN4 exhibits its highest first order hyperpolarizability (β0) value of 9.91 e.s.u. The chromophore BTN3 has the largest second order hyperpolarizability (γ0) value of 11.98 e.s.u and it also has the highest ionization potential (IP) of 5.64 eV, while chromophore BTN4 had a remarkably low EA of −4.91 eV. Their vertical IP (VIP) values ranged from 6.21 eV for BTN1 to 7.56 eV for chromophore BTN7. The chromophore BTN1 displayed a maximum absorption (λmax) at 656 nm with an oscillator strength (f) of 0.0473 and an excitation energy (E) of 1.89 eV. The chromophore BTN4 exhibits a λmax of 366 nm, an f of 0.0012, and an E value of 3.39 eV. The chromophore BTN8 showed the highest λmax value of 1023 nm, an f of 0.0023, and an E value of 1.21 eV.