Time resolved fluorescence anisotropy of basic dyes bound to poly(methacrylic acid) in solution

Abstract

Soluções de poli(ácido metacrílico) atático, PAMA com peso molecular na faixa de (1,6 a 3,4) x 10 5 g mol -1 , e com corantes fluorescentes 9-aminoacridina ou azul do nilo ligados à cadeia, foram estudados por medidas fotofísicas em função da viscosidade e polaridade do solvente. O comportamento dos segmentos da cadeia do PAMA nas vizinhanças da sonda fluorescente foi descrito pela mudança na rotação difusional dos corantes. O etilenoglicol expande a cadeia polimérica quando comparada com a forma mais compactada do corante-PAMA em 50% água/etilenoglicol. A variação do tempo de relaxação rotacional do corante ligado ao PAMA indica uma expansão progressiva da cadeia polimérica para uma forma aberta em etilenoglicol.Solutions of atactic poly(methacrylic acid), PMAA, with molecular weights in the range of (1.6 to 3.4) x 10 5 g mol -1 , and labeled with the fluorescent dyes 9-aminoacridine or Nile blue were studied by photophysical measurements as a function of solvent viscosity and polarity. The conformational behavior of the PMAA chain segments around the fluorescent probe was reported by the change in the rotational diffusion of the dyes. Ethylene glycol swells the polymer chain compared with the more contracted conformation of PMAA in 50% water/ethylene glycol. The change in the rotational relaxation time of the dye bound to PMAA with the decrease of water content in the solvent mixture indicates a progressive expansion of polymer chain to a more open coil form in solution.Keywords: dyes, polyelectrolytes, PMAA, rotational diffusion, solvent friction IntroductionPhotophysical studies of polymers in solution have been extensively reported in recent years. 1,2 Time resolved fluorescence spectroscopy (TRFS) was found to be particularly useful in the study of several types of polymers in solution, and in the presence of additives. 3-10 Time resolved anisotropy decay of a fluorescent probe attached to a polymer chain reflects the rotational relaxation of the probe, and the local dynamics of the polymer segments in solution. 2 The dependence of the segmental dynamics as a function solvent viscosity was studied by TRFS using anthracene attached to 1,2 polybutadiene. 11,12 The polymer local dynamics as well as the structural properties and relaxation processes of polymer and blends were studied by steady state and dynamic fluorescence using anthranyl and pyrenyl groups. [13][14][15] Fluorescence studies of polymethacrylic acid (PMAA) and polyacrylic acid (PAA) containing aromatic fluorescent probes such as naphthalene, anthracene and pyrene have been carried out by many authors to elucidate the properties of those polyelectrolytes in different solvents, pH, and surfactant addition. [16][17][18][19][20] Fluorescence anisotropy reflects the microviscosity and the solubilization dynamics of the probe molecule in solutions of polyelectrolytes. Reports in the literature using polarization and anisotropy of rhodamine 6 G in ethylene glycol demonstrate that the depolarization properties of the probe have relations with the solv...

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