Theoretical Investigation of Optical and Nonlinear Optical (NLO) Properties of 3-Azabenzanthrone Analogues : DFT and TD-DFT Approach.

3-Azabenzanthrone based chromophores are investigated to study the effect of different substituents on optical and "non-linear optical (NLO)" properties by means of density functional theory (DFT) with global hybrid functionals (GHs) - B3LYP and BHandHLYP, range separated hybrid functionals (RSHs) CAM-B3LYP, wB97, wB97X, wB97XD and the basis sets 6-31+G(d), cc-pVDZ, and cc-pVTZ. It is observed that the incorporation of an electron withdrawing group at the 1 position and an electron donating group at the 2 and 6 positions of 3-azabenzanthrone system led to more red shifted absorption maxima and showed better NLO response. Molecule 3 with electron withdrawing -CN at the 1 position exhibited the highest absorption wavelength (lambda= 590 nm). The geometries, dipole moments, HOMO-LUMO energy gaps, total hyperpolarizability are calculated to investigate the effect of different substituents on the photophysical and NLO properties of 3-azabenzanthrone based chromophores. The insertion of -CN group at the 1 position of 3-azabenzanthrone system resulted in higher first order hyperpolarizability (beta(0))(.) The beta(0) values of 3, 5, 6 and 12 are found to be the maximum among other remaining molecules as the "Bond Length Alternation (BLA)" and "Bond Order Alternation (BOA)" parameters tend to zero. The charge transfer (CT) properties of these analogues are established using molecular electrostatic potential (MEP) analysis and quinoidal character at the same level of theory.