Author:

Keywords:

hyper-rayleigh-scattering, terahertz-wave generation, hyperpolarizability tensor components, 2nd-order polarizability tensor, intramolecular charge-transfer, aggregation-induced emission, high-frequency demodulation, transition-metal-complexes, 2nd-harmonic generation, stilbazolium-salt, Science & Technology, Physical Sciences, Chemistry, Organic, Chemistry, HYPER-RAYLEIGH SCATTERING, TERAHERTZ-WAVE GENERATION, HYPERPOLARIZABILITY TENSOR COMPONENTS, AGGREGATION-INDUCED EMISSION, HIGH-FREQUENCY DEMODULATION, CHARGE-TRANSFER MOLECULES, METAL-TO-LIGAND, STILBAZOLIUM-SALT, PUSH-PULL, ELECTROABSORPTION SPECTROSCOPY, 0304 Medicinal and Biomolecular Chemistry, 0305 Organic Chemistry, Organic Chemistry, 3404 Medicinal and biomolecular chemistry, 3405 Organic chemistry

Abstract:

Six new dicationic 2D nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by nucleophilic substitutions of 2,6-dichloropyrazine with pyridyl derivatives. These compounds have been characterized as their PF6- salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Large red shifts in the intense, pi -> pi* intramolecular charge-transfer (ICT) transitions on replacing -oMe with -NMe2 substituents arise from the stronger pi-electron donor ability of the latter. Each compound shows a number of redox processes which are largely irreversible. Single crystal X-ray structures have been determined for five salts, including two nitrates, all of which adopt centrosymmetric packing arrangements. Molecular first hyperpolarizabilities beta have been determined by using femtosecond hyper-Rayleigh scattering at 880 and 800 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly 2D, with dominant "off-diagonal" beta(zyy) components. Stark (electroabsorption) spectroscopic measurements on the ICT bands afford estimated static first hyperpolarizabilities beta(0). The directly and indirectly derived beta values are large, and the Stark-derived beta(0) response for one of the new salts is several times greater than that determined for (E)4'-(dimethylamino)-N-methyl-4-stilbazolium hexafluorophosphate. These Stark spectroscopic studies also permit quantitative comparisons with related 2D, binuclear Ru-II ammine complex salts.