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

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 β_HRS are obtain at the λ_max frequency of each compound. Solvent polarity variation study on β_HRS shows that β_HRS varies linearly with the Kirkwood-Onsagar dielectric factor (D).

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.