Synthesis and Characterization of Carbazole Based Donor-Acceptor-Donor Type Polymer for NLO Applications

Abstract

Carbazole based NLO polymer was synthesized by using Knoevenagel condensation. The polymer is found to be fully soluble in high polar solvents like dimethyl formamide and dimethylsulphoxide. By using GPC and tetrahydrofuran as a solvent, the molecular weight is found to be 5000 g/mol. Thermal analysis exhibited thermal stability of the polymer up to 400 °C and glass transition temperature (Tg) at 214 °C. The polymer film has good optical transparency. The non-centrosymmetry in the film was induced by corona poling for second order NLO property, whereas z-scan technique is used to understand third order NLO property. The effective TPA coefficient (β) found to be 5.1 X 10−12 m/W. Computational study indicated that the total charge is located at the center of the molecule in HUMO case whereas in the case of LUMO the charge is spreads out from the center of the molecule.

Synthesis and Nonlinear Optical Behavior of Thermally Stable Chromophores Based on 9,9-Dimethyl-9H-fluoren-2-amine: Improving Intrinsic Hyperpolarizability through Modulation of “Push–Pull”

“…It has sensitized investigations in the design of new chemical entities having ultrafast response (short response time) as well as high first (quadratic) hyperpolarizability (β, second-order nonlinear polarizability). , One of the strategies for molecular engineering to design the small molecular materials is to append the electron-rich and electron-deficient groups at the two extremes of a π-conjugated linker unit to produce 1D dipolar donor−π–acceptor (D−π–A)-type architectures. , Optimization of molecular NLO response of such dyads is important as these constitute fundamental building blocks for the bulk materials with bulk nonlinear susceptibility . For enhancing the molecular first hyperpolarizability, noncentrosymmetry , of the compounds is an essential prerequisite. However, most “push–pull”-type D−π–A chromophores are inherently centrosymmetric unless an element of dissymmetry is incorporated. , Alternatively, when incorporated in noncentrosymmetric media, such chromophores show second-order nonlinear bulk susceptibility .…”

“… 13 , 14 Optimization of molecular NLO response of such dyads is important as these constitute fundamental building blocks for the bulk materials with bulk nonlinear susceptibility. 15 For enhancing the molecular first hyperpolarizability, noncentrosymmetry 16 , 17 of the compounds is an essential prerequisite. However, most “push–pull”-type D−π–A chromophores are inherently centrosymmetric unless an element of dissymmetry is incorporated.…”