Preparation and characterization of novel polythiophenes bearing oligo(ethylene glycol) spacers and porphyrin units: Optical and electrochemical properties
Résumé
Two thiophene monomers: 3-methyltetra(oxyethylene)oxy-4-methylthiophene (MT) and a monomer containing a meso-3,5-ditert-butyl-tetraphenylporphyrin unit linked via a tetra(ethylene glycol) spacer (MTP) were synthesized and characterized. Both monomers were copolymerized in different ratios MT:MTP (2:1 and 4:1), using FeCl3 as oxidizing agent, to give the corresponding copolymers (CTP-1 and CTP-2). MTP was also homopolymerized under the same reaction conditions to give the homopolymer (PTP). The obtained monomers and polymers were characterized by FTIR, 1H and 13C NMR spectroscopies. On the other hand, the optical properties of the polymers were studied by absorption and fluorescence spectroscopy in THF solution. All polymers exhibited the typical absorption bands of the porphyrin units: a Soret band at λ = 422 nm and four Q-bands between λ = 500 and 700 nm, as well as an additional band at λ = 451 nm, due to the polythiophene backbone. PTP, CTP-1 and CTP-2 showed fluorescence in the region between λ = 500 and 800 nm. Finally, the electrochemical properties of MTP and the obtained polymers were studied by cyclic voltammetry. Tetraphenylporphyrin (TPP) was used as model compound for comparative purposes. The obtained electrochemical data revealed the presence of the redox processes due to the porphyrin and the thiophene units. The reactivity of MTP toward electrochemical polymerization was studied.