Organic Chromophores from D–π–A to D–A’–π–A: Influence of the Auxiliary Acceptor on Energy Levels, Molecular Absorption, and Nonlinear Optical Response

Abstract

In this research article, four organic chromophores of type D–Ai–π–A (i=2–4) combining various auxiliary acceptors (Ai) with phenothiazine (PTZ) as the electron donor, thiophene as the π-conjugated bridge, and tricyanovinyl dihydrofuran (TCF) as the electron acceptor have been structured and theoretically studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The effects of various auxiliary acceptors in D–Ai–π–A chromophores on the nonlinear optical (NLO) response have been examined. In this context, the geometric and electronic structures, intramolecular charge transfer (ICT), NBO analysis, absorption wavelength in different organic solvents, polarizability (α), and hyperpolarizability (β) have been determined. They have been assessed to predict the appropriate candidates for NLO material. The data obtained illustrate that all chromophores with various auxiliary acceptors present a large NLO response ranging from 13541.17 to 66723.38 (a.u), PTZ-2 especially with auxiliary acceptor 2,3-dimethylthieno[3,4-b]pyrazine presents the highest <a> [(879.10 (a.u)) and βtot (66723.38 (a.u)] values. A strong NLO response indicates that this series of organic chromophores with a D-Ai-π-A architecture exhibits large first hyperpolarizability βtot values, which are much greater than those of urea.