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

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 (µ_tot) 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 (λ_max) 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 λ_max of 366 nm, an f of 0.0012, and an E value of 3.39 eV. The chromophore BTN8 showed the highest λ_max value of 1023 nm, an f of 0.0023, and an E value of 1.21 eV.