Star-shaped molecules containing both azochromophores and carbazole units as a new type of photoresponsive amorphous material

Abstract

We synthesized a series of star-shaped molecules containing both azo chromophores and carbazole units (nCz-AZ-X), where n is the number of carbazole units (n = 3 and 6) and X represents cyano (CN) and nitro (NT) as the electron-withdrawing groups on the azobenzenes. The azo compounds existed as amorphous solids at room temperature with glass transition temperatures (T_g) of 89, 86, 74 and 73 °C for 3Cz-AZ-CN, 3CZ-AZ-NT, 6Cz-AZ-CN and 6Cz-AZ-NT, respectively. Thin solid films of the azo molecular glasses were obtained by spin-coating. The formation of the photoinduced self-structured surface patterns was investigated by irradiating the solid thin films of the azo molecular glasses with a uniform laser beam (532 nm, 200 mW cm⁻²) at normal incidence. The formation of surface-relief-gratings (SRGs) was studied by exposing the thin films to an interference pattern of the laser beams (532 nm, 80 mW cm⁻²). The formation of both the self-structured surface patterns and SRGs showed a close correlation with the electron-withdrawing groups of the azo chromophores and the content of the carbazole units in the molecules. The development of these new star-shaped molecules can add a new member to the category of azo molecular glasses and lead to a deeper understanding of the photoinduced effects and their correlation with molecular structures.