Synthesis and surface relief gratings of three-armed star-shaped molecules bearing 4-(N,N-diphenyl)amino-4'-nitroazobenzene chromophores

Three-armed, star-shaped molecules containing 4-(N,N-diphenyl)amino-4'- nitroazobenzene chromophores were synthesized to study the diffraction behavior after inscribing surface relief gratings. The two molecules differed in terms of their mode of chromophore attachment to the core. In compound 5, they were bound to the core laterally through alkylene spacers, whereas the chromophores were tethered perpendicularly to the core in compound 4. Although 60 wt% of the polar azobenzene chromophores was comprised of large molecules, no aggregation behavior was observed in the absorption spectra of the thin films. The surface relief gratings were elaborated on the surface of the molecular films by the two-beam interference method. The dynamics of grating formation were studied in terms of the diffraction efficiency using two different film samples made up of two star-shaped molecules. The maximum diffraction efficiency of D-(ENAZ) ₃, compound 4, was measured to be about 30%, which was significantly high. The mode of chromophore attachment affected the dynamic properties of the diffraction gratings.