Regioisomeric BODIPY derivatives: second-order nonlinear optical properties under an external electric field

Abstract

The present work aims to study the effect of an external electric field as well as arrangement of donor–acceptor groups on the second-order nonlinear optical (NLO) properties of push–pull systems. The first hyperpolarizabilities (β_tot) of acceptor–donor molecules (m-AD and p-AD regioisomers) are investigated based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as the electron-acceptor and benzodithiophene (BDT) as the electron-donor. Calculated results show that the β_tot value (7.49 × 10³ a.u.) of p-AD is larger than that (1.03 × 10³ a.u.) of m-AD. Furthermore, we investigate that the external electric fields (along the positive or the negative directions of x-axis, F_x and F_−x) regulate the NLO properties of the p-AD. (1) As F_x increases, the β_tot values of p-AD are gradually decreased to 0 (F_x ranging from 0 to 30 × 10⁻⁴ a.u.). (2) As F_−x increases, the β_tot values are sharply increased (F_−x ranging from 0 to −30 × 10⁻⁴ a.u.). It is worth noting that the β_tot value is increased to 3.70 × 10⁴ a.u. (F_−x = −30 × 10⁻⁴ a.u.). Moreover, the evolutions of the simulated UV-Vis absorption spectra can well explain the trends of β_tot values under an external electric field. The present work not only provides a deeper understanding of the relationship between structure and NLO properties, but also expands electric field-induced switchable NLO materials.