A novel azobenzene-based amorphous molecular material with a spiro linked bifluorene

Abstract

A novel, high T_g azobenzene-based amorphous molecular material, spiro-ADA, was designed and synthesized via a palladium catalyzed amination reaction. The introduction of bulky spiro linked bifluorene with the non-planar structure of triphenylamine of spiro-ADA prevented crystallization of the molecules and led to good amorphous film formation and thermal stability with a high glass transition temperature of 147 °C. Photoinduced behavior such as optically induced birefringence, diffraction efficiency, and surface relief gratings (SRGs) were investigated in relation to their unique molecular structures. Because of the high concentration of azobenzene groups and a low molecular mass, the films showed a very rapid response to linearly polarized light, a high diffraction efficiency of 38.7%, and a large modulation depth of around 320 nm. In addition, the thermal stability of SRGs inscribed on the spiro-ADA film was measured and found to be very stable below T_g despite its low molar mass and the absence of any chain entanglement.