title: Picosecond dynamics of dimer formation in a pyrene labeled polymer.
abstract: A commercial poly(acrylic acid) (PAA, M(n) = 450 000 g mol(-1)) has been labeled with high levels (9.1 mol %) of pyrene 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.
authors.affiliation: Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Telma
authors.initials: T
authors.lastname: Costa
authors.forename: J
authors.initials: J
authors.lastname: Sérgio Seixas de Melo
authors.forename: Catherine S
authors.initials: CS
authors.lastname: Castro
authors.forename: Sandra
authors.initials: S
authors.lastname: Gago
authors.forename: Martyn
authors.initials: M
authors.lastname: Pillinger
authors.forename: Isabel S
authors.initials: IS
authors.lastname: Gonçalves