resumo
A commercial poly(acrylic acid) (PAA, M(n) = 450 000 g mol(-1)) has been labeled with high levels (9.1 mol %) of pyretic by reaction with 1-pyrenylmethylamine in the presence of boric acid. The modified polymer was found to display an unusual photophysical behavior closely resembling that found for pyrene in constrained environments. The appearance of a band at longer wavelengths in the excitation spectra when collected at the long wavelength emission band was attributed to the spectra of a dimer. The emission of this dimer was particularly enhanced in dioxane:water solvent mixtures with low dioxane content. From time-resolved fluorescence measurements in the picosecond time domain, two decay components were obtained: a fast. decay (4-10 ps) at short wavelengths, which becomes a rising component at longer wavelengths, and a second exponential (2-4 ns) related to the emission of the relaxed dimer. Time-resolved emission spectra were seen to change with time, revealing the emission contribution of two species. This is one of the first reports where the dynamics of dimer formation in a pyrene derivative have been observed.
palavras-chave
STEADY-STATE FLUORESCENCE; WATER-SOLUBLE POLYMERS; EXCIMER FORMATION; CONFORMATIONAL RELAXATION; POLY(ETHYLENE OXIDE); POLY(ACRYLIC ACID)S; CHAIN DYNAMICS; ASSOCIATION; SPECTROSCOPY; PHOTOPHYSICS
categoria
Chemistry
autores
Costa, T; de Melo, JSS; Castro, CS; Gago, S; Pillinger, M; Goncalves, IS
nossos autores
Isabel Maria de Sousa Gonçalves
Professor associado
Martyn Pillinger
Investigador Principalagradecimentos
Financial support from the Portuguese Science Foundation (FCT) through FEDER and FOCI is acknowledged. T.C. and S.G. thank the FCT for Ph.D. (SFRH/BPD/47181/2008) and postdoctoral (SFRH/BPD/25269/2005) grants, respectively.