Nonlinear optical properties and spectroscopic characterization of aniline in singlet, triplet and quintet state using quantum chemical methods

This work reports spectroscopic characterization and nonlinear optical properties of aniline in singlet, triplet and quintet state using quantum chemical methods. Finite field approach has been used for the prediction of spin dependent first (β) and second (γ) hyperpolarizabilities of aniline. The geometrical parameters and vibrational frequencies of aniline in singlet state at B3LYP/6-311++G(df,pd) level from this work are in excellent agreement with the experimental determinations. The dependence of hyperpolarizabilities on method and basis set used for the calculations is shown. Four vibrational modes are blue shifted and remaining red shifted in triplet than the corresponding modes in singlet. The only blue shifted mode in quintet is the C–N in plane bending mode and blue shifted by 30 cm−1. There is no red shift or blue shift observed for the C–H in plane bending and C–H asymmetric stretching modes in quintet. All other modes are red shifted in quintet than the singlet. The β and γ values of aniline in quintet are higher than the singlet. The basis set effects on β and γ are found to be greater than the electron correlation effects. Larger hyperpolarizabilities in quintet than the singlet demonstrates the possibility of spin multiplicity control of hyperpolarizabilities for the aniline.