Viscosity-dependent fluorescent compound fluorescence quantum yield

The fluorescence quantum yields of certain compounds exhibit a strong dependence on the viscosity of the medium. As early as 1913, Stark (5) noticed that some dyes which do not fluoresce in ordinary solvents will, however, fluoresce strongly in highly viscous media such as glycerol at low temperatures. A number of studies on the viscosity-dependence of the fluorescence quantum yields of various compounds have appeared (6-12). Particularly noteworthy among these are the work of Oster and Nishijima (6), Forster and Hoffman (7), and Sharafy and Muszkat (8). However, Loutfy (13,14) was the first to exploit this effect for monitoring polymerization reactions. He applied the viscosity-dependent fluorescence probe approach for study of polymerization of vinyl monomers and discussed the potential of such probes for the study of polymeric systems... 

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