Photoinduced solid-to-liquid transition of an N-benzylideneaniline derivative towards smart glass

Abstract

The potential of azobenzene derivatives that can undergo photoinduced solid-to-liquid transition at room temperature has been demonstrated in many fields such as photo-actuators, energy storage and photo-switchable adhesives. However, both their natural yellowish colour and slow liquid-to-solid phase transition restoration limit their universality in applications. Here, a colourless N-benzylideneaniline derivative molecule with asymmetric side-group substitution (MCN) is synthesized. The small molecular crystal of MCN achieves a reversible photoinduced crystal-to-isotropic liquid transition at room temperature. Due to the short half-life of MCN metastable isomers, the phase transition restoration rate here is significantly faster than that of azobenzene derivatives. As a result, only a single wavelength light source is needed to achieve complete phase change control. The phase transition behaviour of MCN is in situ monitored by using a UV-vis absorption spectrometer in a time-driven mode and a polarizing optical microscope, and its phase transition mechanism is proposed. Furthermore, a smart glass with photo-switchable transmittance is developed by mixing an MCN crystal with a commercial liquid crystal (5CB).