Z-scan and DFT approach for investigating the NLO properties of imidazole fused anthraquinone dyes

Abstract

The NLO characteristics of anthraquinone imidazole-fused D-π-A dyes were investigated by Z-scan and density functional theory (DFT) methods. The electronic and photophysical studies i.e. the intramolecular charge transfer (ICT) characteristics were demonstrated by UV-visible analysis, cyclic voltammetry (CV) study, frontier molecular orbital (FMO), molecular electrostatic potential (MEP) and quinoidal character. Thermogravimetric analysis (TGA) of the dyes 2-(9-phenyl-9H-carbazol-3-yl)-3H-anthra[1,2-d]imidazole-6,11-dione (AQ CBZ) and 2-(4-(diphenylamino)phenyl)-3H-anthra[1,2-d]imidazole-6,11-dione (AQ TPA) revealed high thermal stability. The dye AQ TPA demonstrated strong ICT character with high nonlinear susceptibility χ(3) = 3.50×10−13 e.s.u. The dye AQ CBZ 4.40 J cm−2 showed better optical limiting data relative to AQ TPA. The NLO properties of AQ CBZ and AQ TPA were computed using different DFT functionals with varying Hartree Fork (HF) exchange. The dye AQ TPA revealed superior NLO properties in all the used functionals comparative to AQ CBZ. The long-range corrected (LC) functionals (CAM-B3LYP, ωB97 and ωB97X) exhibited almost equivalent NLO properties as proportional to global hybrid functionals (B3LYP, PBE0, BHHLYP and, M06-HF). The calculated NLO properties were correlated with the reference dye. The DFT findings were appropriately correlated with Z-scan results.