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

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 (beta(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 beta(tot) value (7.49 x 10(3) a.u.) of p-AD is larger than that (1.03 x 10(3) 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 beta(tot) values of p-AD are gradually decreased to 0 (F-x ranging from 0 to 30 x 10(-4) a.u.). (2) As F-x increases, the beta(tot) values are sharply increased (F-x ranging from 0 to -30 x 10(-4) a.u.). It is worth noting that the beta(tot) value is increased to 3.70 x 10(4) a.u. (F-x = -30 x 10(-4) a.u.). Moreover, the evolutions of the simulated UV-Vis absorption spectra can well explain the trends of beta(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.