Fluorescence properties of a ruthenium complex in silane sols and gels at different pH

Silane gels containing ruthenium Ru(bpy)32+ complex were obtained by the sol–gel method. The gelation of sols at different pH values was monitored by fluorescence stationary and time-resolved measurements. In all tested sols a blue shift of fluorescence emission maximum of the fluorophore was observed during the gelation. Changes in λmax on subsequent days of sol–gel transition depended on starting pH of the sol. An increase of the excited state of fluorophore lifetime in the gelation process was observed. When the gelation was finished the lifetime τ1 was constant. A strict correlation between the blue shift of fluorophore emission maximum and changes in the lifetime of ruthenium complex in this system on subsequent days of the sol–gel transition was observed. On this basis, changes in the fluorophore microenvironment in the sol induced by different rates of competing hydrolysis and condensation reactions were discussed.All observed effects were attributed to the interaction of molecules of the ruthenium complex with hydroxyl groups in the gel net.

Research Highlights
► In the submitted article the fluorescence studies of sol-gel transition for various pH of the sol are presented.
► As a probe the ruthenium complex were used.
► The observed phenomena on fluorescence spectra were ascribed to the interaction of fluorophore molecules with silanol groups formed during gelation in the probe microenvironment.