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Published December 17, 2010 | Supplemental Material
Journal Article Open

Syntheses and Properties of Two-Dimensional, Dicationic Nonlinear Optical Chromophores Based on Pyrazinyl Cores

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 PF_6^− salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Large red shifts in the intense, π → π* intramolecular charge-transfer (ICT) transitions on replacing −OMe with –Nme_2 substituents arise from the stronger π-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 β 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" β_(zyy) components. Stark (electroabsorption) spectroscopic measurements on the ICT bands afford estimated static first hyperpolarizabilities β_0. The directly and indirectly derived β values are large, and the Stark-derived β_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 RuII ammine complex salts.

Additional Information

© 2010 American Chemical Society. Received October 5, 2010. Publication Date (Web): November 16, 2010. We thank the EPSRC for support (grants EP/E000738 and EP/D070732) and also the Fund for Scientific Research-Flanders (FWO-V, G.0312.08), the University of Leuven (GOA/2006/3), and the NSF (grant CHE-0802907, Powering the Planet: an NSF Center for Chemical Innovation). I.A. is a postdoctoral fellow of the FWO-V. We thank Dr. Daniela Rusanova-Naydenova for obtaining some of the data presented in Figure 4, and are grateful to Dr Robin Pritchard of the University of Manchester for assistance with solving the crystal structure of salt [2][PF6]2.

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