Steady-State and Dynamic Fluorescence Measurements of a Perylene-Labeled Triblock Copolymer: Evidence for Ground-State Dye Aggregate Formation
1999; American Chemical Society; Volume: 32; Issue: 15 Linguagem: Inglês
10.1021/ma990332s
ISSN1520-5835
AutoresMatthew G. Moffitt, José Paulo S. Farinha, Mitchell A. Winnik, U. Rohr, Kläus Müllen,
Tópico(s)Analytical Chemistry and Sensors
ResumoSteady-state fluorescence and fluorescence decay measurements were carried out on a perylene-labeled triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), both in toluene solution and in a thin film. For the polymer solution, the data fit well to a double-exponential function, and the same two lifetimes τshort = 4.4 ns and τlong = 9.2 ns, but with different relative intensities, are recovered at different emission wavelengths. The longer lifetime, τlong = 9.2 ns, is attributed to the presence of dye aggregates, with τshort = 4.4 ns assigned to unassociated dye. This interpretation of decay profiles is supported by steady-state fluorescence measurements: the onset of aggregate emission corresponds to a sharp decrease in the ratio of preexponential factors, Ashort/Along. Excitation spectra of the labeled polymer are found to be dependent on the emission wavelength, suggesting that the population of aggregated dye molecules exists in the ground state prior to excitation. The fractional contribution of unimer fluorescence in the polymer film (fshort = 0.36−0.10) is much smaller than that in solution (fshort = 0.97−0.84), suggesting a higher degree of aggregate formation in the film.
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