Crystal Engineering of Acentric Styryl Quinolinium Crystals with Strongly Hydrogen-Bonded Phenolic Anions

We report on new acentric styryl quinolinium crystals with phenolic sulfonate counteranions and investigate their supramolecular interactions that affect their quadratic nonlinear optical properties. The phenolic group acting as an electron-donor as well as hydrogen-bond donor site is located at one end of the anion, while the sulfonate group acting as an electron-acceptor as well as hydrogen-bond acceptor site is located at the opposite end of the anion. New styryl quinolinium crystals with 4-hydroxybenzenesulfonate and 6-hydroxynaphthalene-2-sulfonate counteranions exhibit a large macroscopic optical nonlinearity with very efficient second harmonic generation (SHG) efficiency. In styryl quinolinium 4-hydroxybenzenesulfonate crystals, the styryl quinolinium cation chromophores exhibit an acentric ordering with a high order parameter close to 1.0, which is optimal for electro-optic applications or THz-wave generation. The 4-hydroxybenzenesulfonate counteranions form strong head-to-tail hydrogen bonds, and they are also packed in acentric layers. The direction of the polar axes in cation and anion layers is practically identical. Therefore, the introducing phenolic group acting as an electron-donor as well as hydrogen-bond donor to the sulfonate counteranion is a potential technique for crystal engineering to tailor molecular ordering as well as the physical properties of salt-type quinolinium derivatives.