Pyrene-Labeled Water-Soluble Macromolecules as Fluorescent Mimics of Associative Thickeners

Temperature-Controlled Interactions between Poly(N-isopropylacrylamide) Mesoglobules Probed by Fluorescence

“…Information about the mode of excimer formation, either quasi-instantaneous or diffusion controlled, can be gained from the analysis of the rise time of the excimer determined from time-resolved fluorescence decays and from the wavelength of the excimer emission maximum retrieved from the fluorescence spectra. 23,26,28 The photophysical properties of pyrene were exploited recently to monitor PNIPAM samples end-labeled with 1pyrenylbutyl groups acting as hydrophobic substituents. Polymers ranging in molar mass (M n ) from 7.6 to 44.5 kg/mol were prepared and named Py n -PNIPAM, with n equal to 1 or 2, depending on whether one or both ends of the chain were labeled with pyrene.…”

“…Fluorescence spectroscopy is particularly useful to study how hydrophobes interact with each other and with the PNIPAM chain during the heat-induced phase transition of PNIPAM in water. Pyrene, a hydrophobic fluorophore, stands out as a powerful tool to study hydrophobically modified water-soluble polymers in aqueous solution. − The widespread use of pyrene arises from its spectroscopic properties: the high quantum yield (0.32 in cyclohexane) and long lifetime of its emission, the sensitivity of its fluorescence spectrum to the polarity of the local environment, and the ability to form an excited dimer called excimer. − When pyrene absorbs a photon of UV light, either the excited pyrene may fluoresce in the blue region of the visible spectrum as an isolated entity, the monomer, with a lifetime τ M , or it may encounter diffusionally a pyrene molecule in the ground-state and form an excited-state dimer, or excimer. The excimer fluoresces in the green region of the visible spectrum with a lifetime τ E0 .…”

“…A relative measure of the amount of excimer produced can be estimated from the ratio of the excimer-to-monomer fluorescence intensity, the I E / I M ratio, computed from the experimental fluorescence spectra. Information about the mode of excimer formation, either quasi-instantaneous or diffusion controlled, can be gained from the analysis of the rise time of the excimer determined from time-resolved fluorescence decays and from the wavelength of the excimer emission maximum retrieved from the fluorescence spectra. ,, …”