FORMATION OF POLYPYRROLE AND POLYTHIOPHENE WITHIN CU2-MORDENITE AND H+-MORDENITE HOSTS STUDIED BY EPR AND UV-VIS SPECTROSCOPY()

The reactions of pyrrole and thiophene monomers in copper-exchanged mo rdenite have been investigated using EPR and UV-VIS absorption spectro scopy. The EPR spectra show a decrease in the intensity of the Cu2+ si gnal and the appearance of a radical signal due to the formation of ox idatively coupled oligomeric and/or polymeric species in the zeolite h ost. The reaction ceases when ca. 50% of the copper has reacted and di fferences in the form of the residual Cu2+ signal between the thiophen e and pyrrole reactions suggest a greater degree of penetration of the reaction into the zeolite host for pyrrole, in agreement with previou s XPS measurements. The EPR signal intensities show that the average l ength of the polymer chain that is associated with each radical centre is 15-20 and 5-7 monomer units for polypyrrole and polythiophene, res pectively. The widths of the EPR signals suggest that these are at lea st partly due to small oligomers. The UV-VIS absorption spectra of the thiophene system show bands in three main regions: 2.8-3.0 eV (A), 2. 3 eV (B) and 1.6-1.9 eV (D, E, F). Bands A and D-F occur in regions wh ich have previously been observed for small oligomers, 4-6 monomer uni ts in length. Band B is assigned to longer chain polythiophene molecul es. We therefore conclude that the reaction between thiophene and copp er-loaded mordenite produces a mixture of short oligomers together wit h some long chain polythiophene. The UV-VIS spectra of the pyrrole sys tem show bands in the regions 3.6 eV (A), 2.7-3.0 eV (B, C) and 1.5-1. 9 eV (D, F). Assignments of these bands are less certain than for the thiophene case because of the lack of literature data on the spectra o f pyrrole oligomers.