Novel azobenzene precursors for NLO active polyuretanes: Synthesis, quantum chemical and experimental characterization

For the development of electro optical active polyurethanes six new derivatives of 2-{(2-hydroxyethyl)-[4-(4-nitrophenylazo)phenyl]amino}ethanol and two of 2-{(2-hydroxyethyl)-[4-(5-nitropyridin-2-ylazo)phenyl]amino}ethanol were synthesized by azocoupling reaction. Molecular geometry, hyperpolarizability β_FF and ground state dipole moment μ_g were acquired by RHF ab initio (6-31G**) calculations using HyperChem software package. To characterize NLO performance of synthesized azo compounds second order non linear coefficients d₃₁ and d₃₃ were measured as function of chromophore load in guest-host films (PMMA). Eight synthesized compounds can be grouped in four similar gross formula pairs (different position of octyloxy group) with almost equal μ_g β_FF product and different μ_g values. At low chromophore concentrations higher dipole moment compounds perform better. Lower dipole moment compounds have better NLO efficiency at high chromophore loads. Accurate ranking of all chromophores, based on two-level model corrected zero frequency d₃₃(0) values, was not viable due to overestimation of the dispersion factor.