Electrochemical and spectroelectrochemical studies on polythiophene derivatives
The polymerisation of dithienylethylenes (cis and trans 1,2-di(3-thienyl) ethylene, DTE-cis and DTE-trans), thiophene dithiolenes (4,5-dithiophen-3-yl-[1,3] dithiol-2-one, Th-3,3,4,5-di-thiophen-2-yl-[1,3]dithiol-2-one, Th-2,2,4-thiophen-3- yl-5-thiophen-2-yl-[1,3]dithiol-2-one, Th-2,3 and 4,5-di-(5-methyl-thiophen. -3-yl)- [1,3]dithiol-2-one, Th-3,3Me), and nickel dithiolenes (bis[1,2-di(3-thienyl)-1,2-ethenedithiolene] nickel tetrafluoroborate, Ni(Th-3,3)2 and bis[1,2-di(2-thienyl)-1,2-ethenedithiolene] nickel tetrafluoroborate, Ni(Th-2,2)2) was carried out and the resultant polymers were analysed by electrochemical and spectroelectrochemical methods. The voltammetric behaviour of the electropolymerised PDTE-cis and PDTEtrans suggested that polarons and bipolarons were produced upon oxidation. Nevertheless, the formation of a conducting state was not observed in the SNIFTIRS measurements. Upon I2 chemical doping, PDTE-cis and PDTE-trans showed increased stability in the doped state and the SNIFTIRS response of PDTE-trans, revealed similar IR characteristics to those of conductive polymers. The voltammetric and IR behaviour of the dithiolenes, PTh-3,3, PTh-2,2 and PTh-2,3 was similar to that of many conducting polymers. From the UV-Visible spectra of the neutral films it was determined that PTh-3,3, PTh-2,2 and PTh-2,3 have a bandgap of 2.04,2.30 and 2.18 eV, respectively. The electrochemical and SNIFTIRS results for PTh-3,3Me were noticeably different from the other dithiolene polymers revealing a poorly conductive polymer. The solid-state modification of PTh-3,3 to produce a new TTF derivatised polythiophene was carried out. The inclusion of TTF into the PTh-3,3 film was confirmed by voltammetry and IR data that also suggested that only partial modification of the polymer had occurred. The voltammetry of polyNi(Th-3,3)2 and polyNi(Th-2,2)2 showed a redox couple attributed to the electrochemistry of the nickel dithiolene centre, confirming the incorporation of the metal complex into the polymer. Whilst the SNIFTIR spectra of polyNi(Th-3,3)2 showed the characteristic features of metal dithiolenes, the IR behaviour of polyNi(Th-2,2)2 was more comparable to that of conducting polythiophenes. This result indicates that charge delocalisation in polyNi(Th-2,2) occurs through the Ni dithiolene sites disrupting the typical electroactivity of the dithiolene unit. For the polyNi(Th-3,3)2 films, the nickel dithiolene sites seem to be electronically isolated, preserving the aromaticity of the dithiolene system.