Evaluation of the second-order nonlinear optical properties of oxasmaragdyrin-BODIPY derivatives

Using (time-dependent) density functional theory (DFT) methods, we shed light on the electronic and nonlinear optical (NLO) properties of four (BF₂)-oxasmaragdyrin-(3-pyrrolyl) BODIPY derivatives. The static first hyperpolarizabilities (β_tot) and hyper-Rayleigh scattering hyperpolarizabilities (β_HRS) of expanded porphyrins increase in the order 1 < 2 < 3 < 4. The unit sphere representations further clearly exhibit a remarkable increase in the NLO response from 1 to 4. Noteworthily, the BF₂ group and the pyrrole ring yield a positive effect on the enhancement of hyperpolarizabilities of expanded porphyrins. Furthermore, the hyperpolarizability in the static limit is evaluated using the two-state approximation. The calculation results show that four complexes have large HRS hyperpolarizabilities due to the lower excitation energy for the crucial excited state. Furthermore, the HOMO-LUMO energy gap and charge transfer excitation length correlate well with the β_HRS response.