A computational study of the nonlinear optical properties of carbazole derivatives: theory refines experiment

The nonlinear optical (NLO) properties of N-ethyl dicyanocarbazole (1), N-ethyl cyanoethylacetatecarbazole (2), and N-ethyl dimethylacetatecarbazole (3) are studied with traditional hybrid and long-range corrected (LC) density functional theory (DFT) methods. The carbazoles are predicted to have planar structures with a high degree of π-conjugation and charge transfer, resulting in measurable NLO responses. The DFT data here calculated allow us to refine and correct previously reported experimental hyperpolarizabilities for these compounds. Experimental UV–vis absorption bands (related to hyperpolarizabilities estimated via solvatochromism) are also accurately reproduced by LC-DFT when using gap fitting schemes. The effects of different functionals on the HOMO–LUMO energy gaps and eventually on the total hyperpolarizabilities are discussed.