Synthesis, crystal growth, and second-order nonlinear optical properties of new pyridinium salts

Abstract

Three series of new organic pyridinium salt chromphores with high nonlinearities and crystal growth characteristics have been designed and synthesized through modifying the cations and counteranions. The chromophores with strong coulomb interactions to surpass the intermolecular interaction have been adopted to induce the non-centrosymmetric packing of molecules which is advantage to high macroscopic second-order optical nonlinearities. At the same time, heterocycle was introduced to substitute phenyl group of the DAS (4-N, N-dimethylamino-4′-N′-methyl-pyridinium tosylate) cation, which can form a series of new pyridinium-based chromophores to extend the molecular structure of NLO materials. Kurtz powder tests revealed that out of these pyridinium salts, the maximum powder second harmonic generation (SHG) efficiency is 1300 times of urea standard at the non-resonant wavelength of λ=2109 nm. The effect of heterocycle on the nonlinear properties and crystal growth abilities of the new developed materials have been studied. Single crystals were successfully obtained from methanol by slow cooling and evaporation methods. The reasons for considerably different macroscopic nonlinearities of these compounds have been explored in terms of intermolecular interactions.