Síntese e caracterização espectroeletroquímica de derivados eletrocrômicos e fluorescentes de polipirrol e politiofeno

Abstract

The electrochemical and optical properties of poly[3-(N-pyrrolyl)propyl dansylglicinate] (PDGP) films prepared by electrochemical polymerisation in acetonitrile (CH3CN)/boron trifluoride diethyl eterate (BFEE) were investigated. The PDGP films presented electrochromic behaviour, changing their colour from greenish-yellow to greyish-blue at the neutral and oxidised states, respectively, being fluorescent properties with emission in λ = 562 nm in dichloromethane CH2Cl2 solution. The poly[2-(3-thienyl)ethyl dansylglycinate] (PDGTE) deposited onto ITO by casting were also electrochromic, with colour varying from yellow to bluish-grey at the neutral and oxidised states, respectively, besides present yellow light emission (λ = 547 nm) in CH2Cl2 solution. Therefore, the properties presented by PDGP and PDGTE films make them potential candidates for application in displays and optoelectronic devices. Besides that, an unprecedented monomer and its respective polymer, the 3-(1-pyrrolyl)propyl-N-(2-[4-(dimethylamino) phenylazo benzoate] (MRPy) was synthesised with 57 % yield. The polymer PMRPy was chemically synthesised by using an usual polymerisation route involving the monomer oxidation with FeCl3. The PMRPy was also prepared by electrochemical polymerisation in CH3CN/ BFEE. The monomer and polymer were characterised by conventional methods of analysis of organic compounds, as 1H NMR, 13C NMR and FTIR. The films of polypyrrole (PPy) and PPy doped with Methyl red (PPy/MR) were prepared in order to compare their electrochromic properties with the films of PMRPy. It was observed colour changes for the PMRPy films, from the yellow color in the reduced state to dark magenta in the oxidised state, whilst the PPy/MR films showed colour variation from yellow in the reduced state to magenta in the neutral state, and a bluish-gray color in the oxidised state. The colour changes PMRPy films were also investigated after exposure to HCl vapours presented dark magenta color fading to yellow when immersed in 0.1 mol L-1 NaOH solution. The characteristics presented by the PMRPy film make this material a good candidate for application as active layers in optoelectronic devices, pH sensors, as well as magenta-colored films derived from polypyrrole, very limited in the literature.