Synthesis, crystal structures, and solid state quadratic nonlinear optical properties of a series of stilbazolium cations combined with gold cyanide counter-ion

Abstract

Three salts built up from (E)-4′-(dimethylamino)-stilbazolium (DMAS)H⁺, (E)-4′-(diethylamino)-stilbazolium (DEAS)H⁺, (E)-4′-{2-(methoxymethyl) pyrrolidinyl}-stilbazolium (MPS)H⁺, and gold cyanide as a counter-ion, are reported. The crystal structures have been solved for (DEAS)H⁺ Au(CN)₂⁻ (Cc space group), and for (MPS)H⁺ Au(CN)₂⁻ (P1 space group). The semi-empirical (ZINDO) calculated static hyperpolarizability (β₀) of (MPS)H⁺ is equal to 147 × 10⁻³⁰ cm⁵esu⁻¹, in solid state, which is 25% higher than that of the cation of the well known (E)-4′-(dimethylamino)-methylstilbazolium tosylate (DAST). (MPS)H⁺ Au(CN)₂⁻ exhibits a unique crystal structure in which the cations are perfectly aligned. This combination of large hyperpolarizability and strict 1-dimensional character leads to a giant d_zzz quadratic susceptibility (χ⁽²⁾) tensor component estimated between ∼4500 pm V⁻¹ (∼11 × 10⁻⁶ esu) and 12 400 pm V⁻¹ (∼30 × 10⁻⁶ esu) at 1.064 μm, by a confocal μ-SHG technique. The use of such material in ultra-thin devices is critically evaluated.