Octupolar (<i>C</i><sub>3</sub> and <i>S</i><sub>4</sub>) Symmetric Cyclized Indole Derivatives: Syntheses, Structures, and NLO Properties

Several cyclized indole derivatives have been synthesized, and their structures been determined. The <i>C</i><sub>3</sub>-symmetric single-chiral <i>N</i>-phenyltriindole (Tr-Ph3) crystallized in the <i>P</i>1 space group, and the <i>S</i><sub>4</sub>-symmetric saddle-like tetraindole (TTr) crystallized in the <i>I</i>4̅ space group. The Tr-Ph3 and TTr crystals exhibit remarkable powder SHG intensities 5 and 11 times that of KH<sub>2</sub>PO<sub>4</sub> (KDP), respectively. TTr is a useful octupolar core to build <i>S</i><sub>4</sub>-symmetric molecules and crystals for second-NLO materials.