Molecular bodipy-based rotors as promising viscosity sensors
Creating materials with specific properties is the most important task of modern chemistry and materials science. “Nano assembling” with sol-gel precursors is one of the methods to obtain multifunctional materials. Production of materials with desired properties requires covalent or non-covalent functional molecules immobilization into the polymer matrix. In this context, the control over hydrolysis and polycondensation processes in sol-gel systems to increase the efficiency of hybrid materials synthesis and their implication characteristics gets new particular importance.
Organic dyes may be the objects of immobilization, among which there are boron fluoride complexes of dipyrrins (Bodipy) characterized by intensive chromophore and fluorescent properties as well as high quantum yield. Bodipy with a phenyl substituent in the meso-position in dipyrrin system was assumed to be used as a molecular rotor. Molecular rotors are fluorescent molecules, parts of which are able to rotate relative to each other resulting in nonradioactive energy dissipation of the excited state of the molecule that reduces the emissivity of the compound. Fluorescence characteristics of these compounds are largely determined by the properties and, above all, the viscosity of the medium. Molecular rotors properties make Bodipy a promising compound for immobilization into a polymer matrix. It gives both specific functional properties and the opportunity to study and control sols and gels formation in such systems.
Spectral and fluorescent properties of meso-phenyl substituted Bodipy were studied in a model system of ethanol-ethylene glycol with various component ratios at different temperatures, changes in fluorophore spectral characteristics at different dynamic viscosity of the system being recorded. Both fluorescence intensity and the relative quantum yield of meso-substituted Bodipy were found to be greatly dependent on the solution viscosity. The fluorescence dependence on the solvents amounts is of an extreme character due to the changes in the intermolecular interactions. The changes in temperature caused linear variations of the fluorescence intensity for meso-phenyl substituted Bodipy. Similar changes were observed for the values of the quantum yields. The revealed dependence of fluorescence characteristics on dynamic viscosity indicated the possibility of using meso-phenyl substituted Bodipy to determine local viscosity in the solution and produce hybrid functional materials that will be used in future.
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