First Theoretical Framework of Triphenylamine-Dicyanovinylene-Based Nonlinear Optical Dyes: Structural Modification of π-Linkers

This work was inspired by a previous report [Janjua, M.R.S.A. Inorg. Chem. 2012, 51, 11306-11314] in which the nonlinear optical (NLO) response strikingly improved with double heteroaromatic rings. Herein, series of triphenylamine-dicyanovinylene based donor-pi-acceptor dyes had been designed by structural tailoring of pi-conjugated linkers and theoretical descriptions of their molecular NLO properties were reported. Density functional theory and time-dependent density functional theory calculations were performed on optimized geometries to elucidate the electronic structures, absorption spectra, and NLO properties and also to shed light on how structural modification influences the NLO properties. The simulated absorption spectra results indicate that all of the dyes showed the maximum absorbance wavelength in the visible region. The lowest unoccupied molecular orbital-highest occupied molecular orbital energy gaps of all of the dyes have been found smaller, which results in large NLO response. Calculation of natural bond orbital analysis reveals that electrons successfully migrated from donor to acceptor via pi-conjugated linkers and a charge separation state was formed. High NLO response revealed that this class of metal free organic dyes possess eye-catching and remarkably large first hyperpolarizability values, especially D8 with highest <alpha > and beta(tot) computed to be 771.80 and 139 075.05 au, respectively. Our research presented a vital confirmation for controlling the kinds of pi-conjugated linker that was a significant approach for the design of new appealing NLO compounds. This theoretical framework also highlighted the NLO properties of organic dyes that can be valuable for their uses in modern hi-tech applications.