Molecular Alignment of 4-(Dimethylamino)-4′-Nitroazobenzene Molecules through Pillararene-Based Host–Guest Complexation for Improvement of Nonlinear Optical Properties

Controlling molecular arrangement in organic nonlinear optical (NLO) materials represents a critical challenge for achieving enhanced NLO performance. We report a host–guest recognition system employing propoxylated pillar[5]arene (PrP5) to precisely modulate the solid-state NLO properties of an azobenzene dye─4-(dimethylamino)-4′-nitroazobenzene (DNAB). Single-crystal X-ray analysis unambiguously confirms the formation of a 1:1 inclusion complex (PrP5⊃DNAB) with remarkable structural regularity. The crystal structure reveals that DNAB molecules adopt uniform orientations within the one-dimensional nanochannels formed by PrP5 molecules in the solid state, creating an optimal acentric arrangement that significantly enhances the NLO response. This work establishes pillararene-based cocrystal engineering as a powerful strategy for controlling molecular ordering and photophysical properties in the solid state, opening new avenues for the development of high-performance NLO materials.