This study reports a design strategy for efficient organic nonlinear optical crystals with a large macroscopic optical nonlinearity. In organic ionic crystals, edge-to-face π-π interactions between the cations and the anions contribute to decrease macroscopic optical nonlinearity, because they hinder supramolecular charge-transfer propagation. However, most the benchmark nonlinear optical crystals have been planar-shaped anions based on benzenesulfonate and naphthalenesulfonate, which may lead to increase of edge-to-face π-π interactions. To reduce edge-to-face π-π interactions, non-planar-shaped benzenesulfonate anion with trifluoromethoxy group having near-orthogonal conformations on aromatic rings is introduced. 4-(trifluoromethoxy)benzenesulfonate (OCF3) anions successfully widen the distances between the cations and the anions in the crystal, which lead to decrease of edge-to-face π-π interactions between the cations and the anions. 2-(4-hydroxystyryl)-1-methylquinolin-1-ium 4-(trifluoromethoxy)benzenesulfonate (OHQ-OCF3) crystals exhibit a larger macroscopic optical nonlinearity than 2-(4-hydroxystyryl)-1-methylquinolin-1-ium 4-methylbenzenesulfonate (OHQ-T) crystals having benchmark planar-shaped benzenesulfonate anion.
