title: Star-shaped molecules with polyhedral oligomeric silsesquioxane core and azobenzene dye arms.
abstract: We synthesized a series of hybrid nanomaterials combining organic dyes with polyhedral oligomeric silsesquioxanes (POSS) based on three different azobenzenes: monoazobenzene (4-phenylazophenol), bis-azobenzene (Disperse Yellow 7 and Fast Garnet derivative), and push-pull azobenzene (Disperse Red 1) via hydrosilylation coupling. The azo-functionalized POSS compounds possess high thermal stability, and their branched architecture resulted in effective suppression of molecular aggregation and allowed for direct imaging of individual dye-POSS structures with expected molecular dimensions. Stable, uniform, smooth, and ultrathin nanocomposite films with mixed silica-organic composition and relatively low refractive indices can be fabricated from all azo-POSS branched conjugates. Finally, the photoisomerization behavior of POSS-conjugated 4-phenylazophenol was investigated in solution as well as in ultrathin nanocomposite film. We found that conjugation to POSS core did not affect the kinetics of trans-cis photoisomerization and thermal cis-trans relaxation. Furthermore, rapid and reversible photoisomerization was observed in azo-POSS nanocomposite films. We suggest that the highly stable branched azo-POSS conjugates with high dye grafting density described here can be considered for nanometer-sized photoswitches, active layer material with optical-limiting properties, and a medium with photoinduced anisotropy for optical storage.
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Petr A
authors.initials: PA
authors.lastname: Ledin
authors.forename: Ihor M
authors.initials: IM
authors.lastname: Tkachenko
authors.forename: Weinan
authors.initials: W
authors.lastname: Xu
authors.forename: Ikjun
authors.initials: I
authors.lastname: Choi
authors.forename: Valery V
authors.initials: VV
authors.lastname: Shevchenko
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Tsukruk