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 pi-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.