Azobenzene molecular glasses with tuned glass transition temperatures: from optimal light-induced motion to self-erasable gratings

Abstract

The rate of photomechanical formation of surface relief gratings (SRG) in thin films of azobenzene materials depends on their glass transition temperature (T_g), with an optimal T_g around 50–60 °C yielding the fastest SRG growth. Herein, the SRG growth of five analogous Disperse Red 1 molecular glasses with T_g values ranging from 9 to 71 °C was studied with two different laser wavelengths (488 and 532 nm). It was found that the optimal T_g for SRG growth increases with laser irradiance, from approximately 50 °C at 100 mW cm⁻² to over 70 °C at 300 mW cm⁻². Furthermore, the azobenzene glass with a sub-ambient T_g of 9 °C can inscribe self-erasable gratings that collapse spontaneously when irradiation is stopped in a repeatable fashion, thereby paving the way for light-controlled optical devices.