Effect of charge transfer on the first hyper-polarizability of N,N-dimethylaniline and julolidine: a DFT based comparative study.

Context: Quantum mechanical calculations involving electron correlation, frequency dispersion, and solvent effects were carried out to examine the second-order nonlinear optical response of various acceptor, X (-CF3, -CN, -NO2) substituted in N,N-dimethylaniline (DMA) and julolidine(JLD). Here, both DMA and JLD acts as donor and the three substituted groups, X (-CF3, -CN and -NO2) at the para position of both the ring systems as acceptor. The NLO response (βHRS) of -CF3 and -CN substituted DMA and JLD is relatively lower compared to DMA-NO2 and JLD-NO2. The charge distribution is found higher in case of -NO2 substituted DMA and JLD (±443 and ±449) compared to their -CF3 or –CN substitution. Electronic characteristics such as UV-Vis absorption spectra, crucial excited state parameters and charge transfer contribution to βHRS have been used to explain the NLO parameter of DMA-X and JLD-X. Variation of the incident optical frequency of light shows fluctuation of βHRS value and highest values of βHRS are obtain at the λmax frequency of each compound. Solvent polarity variation study on βHRS shows that βHRS varies linearly with the Kirkwood-Onsagar dielectric factor (D). Methods: All computational studies have been carried out using density functional theory (DFT) based method. Since CAM-B3LYP based hybrid functional improves the asymptotic behavior of the exchange interaction by dividing into short-range and long-range components, first hyperpolarizability values in the present study were computed using DFT/ CAM-B3LYP/ 6-31G+(d,p) level of theory. [ABSTRACT FROM AUTHOR]