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

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 degrees 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 degrees 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 degrees C at 100 mW cm(-2) to over 70 degrees C at 300 mW cm(-2). Furthermore, the azobenzene glass with a sub-ambient T-g of 9 degrees 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.