Study of self-defocusing, reverse saturable absorption and photoluminescence in anthraquinone PMMA nanocomposite film

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⁽³⁾ in AQ1 3.43 × 10^-13 e.s.u relative to the dye AQ2 which has only ESIPT core. But, the dye AQ2 6.27 J cm^-2 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.

Role of annealing on the structural and optical properties of nanostructured diaceto bis-benzimidazole Mn(II) complex thin films

A coordination complex, manganese incorporated benzimidazole, thin films were prepared by chemical bath deposition method. Structural characterization of the deposited films, carried out by Fourier transform infrared spectroscopy, Raman and electron paramagnetic resonance spectral analyses, reveals the distorted tetrahedral environment of the metal ion with bis-benzimidazole ligand. Further the molecular composition of the deposited metal complex was estimated by energy-dispersive X-ray spectroscopy. The prepared thin films were thermally treated to study the effect of annealing temperature on the surface morphology and the results showed that the surface homogeneity of the films increased for thermally treated films up to 150°C. But distortion and voids were observed for the films annealed at 200°C. The Raman analysis reveals the molecular hydrogen bond distortion which leads to the evaporation of the metal complex from the thin film surface with respect to annealing temperature. The linear and nonlinear optical properties of the as prepared and annealed films were studied using ultraviolet-visible transmittance spectroscopy, second harmonic generation and Z-scan analyses. Films annealed at 150°C show a better linear transmittance in the visible region and larger SHG efficiency and third order nonlinear susceptibility when compared with the other samples. Further, the film annealed at 150°C was subjected to optical switching analysis and demonstrated to have an inverted switching behavior.

Spectral, morphological, linear and nonlinear optical properties of nanostructured benzimidazole metal complex thin films

Metal organic materials are widely investigated to find their suitability for nonlinear optical applications due to the advantage of combined organic and inorganic properties. In this work benzimidazole based metal organic thin films of dichlorobis (1H-Benzimidazole) Co(II) and dichlorobis (1H-Benzimidazole) Cu(II) were deposited by chemical bath deposition method. The deposited films were annealed at 100, 150 and 200 °C to investigate the effect of annealing on the properties of thin films. Surface homogeneity of the films was increased with the annealing temperature due to the surface diffusion of the films and the same was evidently shown by Raman spectroscopy and Atomic Force Microscopy studies. But annealing the films at 200 °C yielded bulk patches on the surface due to the distortion of molecules. Linear and nonlinear optical properties of the films annealed at 150 °C showed relatively higher transmittance and improved nonlinear optical properties than the other as prepared and annealed samples.