Mesoporous materials incorporating a zinc(II) complex: Synthesis and direct luminescence quantum yield determination

New luminescent inorganic–organic hybrid materials incorporating the luminescent zinc(II) complex ZnL2 (λem = 457 nm and Φem = 4.4% reference values for ZnL2; HL = chelating ligand resulting from the reaction between salicylaldehyde and 3-aminopropyltriethoxysilane), covalently bonded to different types of mesoporous silica hosts (namely MCM-41, MCM-48 and SBA-15), were prepared via both the methods of grafting post-synthesis (GPS) and one-pot synthesis (OPS). The products obtained, which form the GPS [(GPS)(Zn/MCM-41), (GPS)(Zn/MCM-48), (GPS)(Zn/SBA-15)] and the OPS [(OPS)(Zn/MCM-41), (OPS)(Zn/MCM-48), (OPS)(Zn/SBA-15)] series, contain the ZnL2 guest covalently bonded to the silica framework through silicon–oxygen bonds formed when the silane group is placed at the periphery of the Zn(II) coordination sphere. GPS and OPS materials were characterized by powder X-ray diffraction, N2 adsorption/desorption, thermogravimetric analysis (TGA) and UV/vis spectroscopy. For the new mesoporous materials the emission quantum yield (EQY) was measured by means of an integrating sphere combined with a spectrofluorimeter. The ZnL2 loading (measured by the ZnL2/SiO2 ratio calculated from TGA data) for MCM-41 appears to be independent of the synthesis procedure, whereas, for both MCM-48 and SBA-15, the ZnL2/SiO2 ratio of the materials obtained via OPS is about four times higher than products obtained from GPS. The ZnL2 loaded GPS and OPS series show λem maxima at about 485 and 455 nm, respectively. Moreover, with reference to EQY (GPS)(Zn/SBA-15) and (OPS)(Zn/SBA-15), although featuring ZnL2/SiO2 ratios of 0.13 and 0.45, respectively, they showed similar EQY values: 2% and 5%. On the contrary, (GPS)(Zn/MCM-41) and (OPS)(Zn/MCM-41) which give similar ZnL2/SiO2 ratios (0.09 and 0.14) exhibit very different EQY, i.e. 2% and 22%, respectively.