NLOphoric imidazole-fused fluorescent anthraquinone dyes.

The Z-scan and DFT techniques were explored to investigate the non-linear optical properties of anthraquinone fused imidazole-based D-π-A dyes. With the help of UV-visible spectral analysis, pH study, CV analysis, HOMO-LUMO interaction, MEP plots, and quinoidal character the influence of intramolecular charge transfer characteristics and H-bonding process on electronic and photophysical studies of anthraquinone derivatives were understood. The dyes 2-(4-(diethylamino)-2-hydroxyphenyl)-3H-anthra[1,2-d]imidazole-6,11-dione (AQ1) and 2-(2-hydroxynaphthalen-1-yl)-1H-anthra[1,2-d]imidazole-6,11-dione (AQ2) displayed a single emission with pronounced Stokes shift and thermal stability (upto 290 °C). The dye AQ1 exhibited strong charge transfer character which is explained by the ICT process leading to high nonlinear susceptibility χ in AQ1 3.43 × 10 e.s.u relative to the dye AQ2 which has only ESIPT core. But, the dye AQ2 6.27 J cm showed better optical limiting value. The NLO properties of AQ1 and AQ2 were computed by DFT functionals based on Hartree Fork (HF) percentage exchange. The dye AQ1 exhibits noticeable NLO properties. The global hybrid functionals with HF composition beyond 50% (BHHLYP, M06-HF) and the long rang corrected functionals (CAM-B3LYP, ωB97, and ωB97X) demonstrated comparable NLO properties relative to B3LYP and PBE0. It was observed that the combined effect of ICT and the H-bonding cores enhance the NLO properties. The experimental findings (Z-scan) were successfully correlated with theoretical (DFT) results.