Well-Defined Pillararene-Based Azobenzene Liquid Crystalline Photoresponsive Materials and Their Thin Films with Photomodulated Surfaces

Photoresponsive materials (PRMs) have long been a hot topic and photo-modulated smart surface is very appealing. Particularly, liquid crystalline PRMs are able to amplify and stabilize photoinduced orientation thanks to their self-assembling and ordering characteristics. Herein, the first pillararene-based azobenzene liquid crystalline PRM with well-defined structure is presented, which can avoid the usually ill-defined composition drawback of polymer PRMs and prevent the severe H-aggregation from suppressing or even completely blocking photoresponse in simple azobenzene derivatives. The pillar[5]arene-based macrocyclic azobenzenes with variant length spacers show wide temperature range smectic liquid crystalline mesophases and excellent film-formation property. The tubular pillar[5]arene macrocyclic framework provides sufficient free volume for azobenzene moieties to achieve reversible photoisomerization and photoalignment; thus, their thin films demonstrate excellent light-triggered modulation of surface free energy, wettability, and even photoalignment-mediated orientation of an upper layer discotic liquid crystal columnar mesophase. Such pillararene-based azobenzene liquid crystals represent novel and promising PRMs with extensive fascinating applications.