Polystyrene, fluorescence excited species

Excitation Spectra and Fluorescence Lifetimes. In this section, we further examine adsorption onto colloidal polystyrene by investigating the excitation spectrum of the adsorbed species. In Figure 7a, we show the excitation spectra of Py-PEG-Py(4250) before and after the addition of polystyrene particles. The spectrum undergoes a substantial red shift upon adsorption the main peak moves approximately 4 nm. A similar effect is found in the complexation with PMAA, as shown in Figure 3, where the monomer spectrum is again shifted to higher wavelengths. From these spectral shifts, we infer a spectral sensitivity to the environment. This sensitivity is illus-... 

In another type of application a low molecular fluorescent probe is added to a system containing macromolecules. As would be expected, the rotation of a small species is insensitive to the molecular weight of high polymers, but depends on the "microscopic viscosity" which is a function of free volume. For instance, Nishijima has shown that the microscopic viscosity of liquid paraffin hydrocarbons levels off for molecular weights above 1000 and that the microscopic viscosity of polystyrene containing 10 volume"/ benzene is only 200 times as high as that of benzene (15). Nishijima also showed that the emission anisotropy is a useful index of molecular orientation. Since both the excitation and the emission are anisotropic, the method yields the fourth moment of the distribution function of orientations, while other optical properties (dichroism, birefringence) depend on the second moment (15). 

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