Synthesis and photophysical properties of pyrene-functionalized nano-SiO2 hybrids in solutions and doped-PMMA thin films

Luminescent pyrene-functionalized nano-SiO2 (nano-SiO(2)Pyr) hybrids were synthesized and characterized using thermogravimetry, infrared, UV-vis absorption and, X-ray photoelectron spectroscopy, as well as field emission transmission electron microscopy (FETEM). The organic substituents immobilized on the nano-SiO(2)Pyr hybrids accounted for approximately 10% of the total weight. Polyethylene glycol 200 (PEG200) was found to be the most suitable solvent to suspend the nano-SiO(2)Pyr hybrids compared to other commonly used organic solvents. FETEM images indicated an average SiO2 nanoparticle diameter of approximately 12 nm and a 1- to 2-nm thick organic species functionalization layer. Several emission peaks were recorded at wavelengths of 380-580 nm and were designated as emissions arising from either the monomer or excimer of the pyrene substituents. Excimer formation was concentration and solvent polarity dependent, with higher concentrations and a stronger solvent polarity benefiting excimer formation. Further, nano-SiO(2)Pyr hybrids were doped in poly(methyl naethacrylate) (PMMA) thin films; fluorescence spectra indicated that the excimer could be formed almost exclusively from neighboring nano-SiO(2)Pyr hybrids. Time-resolved fluorescence decays revealed that the emission lifetimes of nano-SiO(2)Pyr monomers and excimers were approximately 190 ns and 65-100 ns in the PEG200 solution, respectively, which was shortened to 0.45 ns to tens of ns in doped PMMA thin films, depending on the nano-hybrid concentration. Thus, the present study not only provides a method to prepare luminescent nano-materials but also a route to investigate excimer formation in solutions and thin films. (C) 2016 Elsevier B.V. All rights reserved.