Octupolar Molecules for Nonlinear Optics: From Molecular Design to Crystals and Films with Large Second‐Harmonic Generation

We summarize the nonlinear optical ( NLO ) properties of octupolar molecules, crystals, and films developed in our laboratory. We present the design strategy, structure–property relationship, and second‐order NLO properties of 1,3,5‐trinitro‐ and 1,3,5‐tricyano‐2,4,6‐tris( p ‐diethylaminostyryl)benzene ( TTB ) derivatives, TTB crystals, and films prepared by free‐casting TTB in poly(methyl methacrylate) ( PMMA ). The first hyperpolarizability of TTB was fivefold larger than that of the dipolar analogue. Moreover, the TTB crystal showed unprecedentedly large second‐harmonic generation ( SHG ). While TTB crystal films (20 wt% TTB/PMMA ) on various substrates showed appreciable SHG values, the cylinder film exhibited much larger SHG values and large electro‐optic ( EO ) coefficients. The large SHG values and EO coefficients, as well as the high thermal stability of the cylinder film, will make it a potential candidate for NLO device applications.