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 βFF and ground state dipole moment μg 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 μg βFF product and different μg 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.