Investigation of new push–pull pyridine-1-oxide derivatives as 1D NLO chromophores with vanishing dipole moment

Abstract

The non-linear optical properties of new one-dimensional (1D) hyperpolarizable chromophores bearing a pyridine-1-oxide donor group and a 4-nitrophenyl acceptor group, linked by CC or NN double bonds have been studied. These molecules present a true intramolecular donor/acceptor charge transfer (ICT) leading to high β hyperpolarizability, but unlike the classical ICT chromophores exhibit a vanishing dipole moment μ. Such a property can lead to a better control of the non-centrosymmetric alignment of the hyperpolarizable chromophores in the solid state, as observed previously in 3-methyl-4-nitropyridine-1-oxide crystals (POM). Due to the lack of dipole moment β cannot be measured by EFISHG. In this paper, the synthesis, modeling of μ and β, and hyper-Rayleigh scattering (HRS) hyperpolarizability measurements of 4′-nitro-4-stilbazole- N-oxide and its azo analogue, as two representative chromophores in this series, are reported. The values are compared with these of the polar analogue 4-methoxy-4′-nitrostilbene (MONS). Hartree-Fock calculations confirm their vanishing dipole moment and give β-values in good accordance with those obtained experimentally by HRS. Longer 1D chromophores in this series are currently under investigation.