Synthesis and properties of 2-dicyanomethylenethiazole merocyanines

Abstract

Second-order nonlinear optical (NLO) polymers are emerging materials for next generation photonic and optoelectronic devices. The synthesis of high figure of merit (μ.β 0 ) chromophores is crucial to the preparation of such materials, and we have previously reported the facile synthesis of a suite of chromophores with μ.β 0 values of approx. 10,000 x 10 -48 esu. These chromophores possess high permanent dipole moments, a property that, when combined with the high first order polarisability of these molecules, results in high NLO susceptibilities in a spatially ordered arrays of these compounds. However, their high permanent dipole moment renders them susceptible to dimerization and aggregation which has the undesirable effect of cancelling the hyperpolarizability vector associated with these molecules thereby reducing the bulk second order NLO susceptibility.Theoretical and experimental investigations have determined that the electro optical activity of NLO chromophores can be maximised through shape modification. The introduction of bulky substituents onto selected chromophore has been shown to cause the molecular shape to become more spherical (oblate) in nature, and in doing so, this limits intermolecular interactions. Previous work has focussed on the introduction of bulky substituents in order to diminish aggregation. We report here on the synthesis of thiazole based zwitterionic chromophores containing bulky substituents and their spectroscopic properties.