Electrochemical and photoelectronic studies on C60-pyrrolidine-functionalised poly(terthiophene)

A novel donor-acceptor poly(terthiophene) derivative bearing a C60 pendant was electropolymerizated from N-methyl-2-(2-[4,4′’-didecyloxy-2,2′;5′,2′’]terthiophen-3′-yl-ethenyl)fullero[3,4]pyrrolidine (TTh–C60) solution. The electroreduction of TTh-C60 and poly(TTh-C60) showed the presence of complex peaks related to fulleropyrrolidine reduction. The dual nature of these redox couples may be related to increasing Coulombic repulsion or coupling between C60 substituents. Electrochemical, X-Ray photoelectron spectroscopy (XPS), Ultra-Violet photoelectron (UPS) and UV-Vis spectroscopy also confirm the nature of poly(TTh-C60). Electrochemical band gap of poly(TTh-C60) is 0.63 ± 0.20 eV in TBAP electrolyte and propylene carbonate (PC) solution. Furthermore, we obtained the value of optical energy band gap (Eopt = 0.59 ± 0.03 eV), the transport energy band gap (Egtrans = 1.17 ± 0.20 eV) and the exciton binding energy (Eb = 0.58 ± 0.20 eV) for poly(TTh-C60). The ionization energy values (IE) were determined using UPS spectroscopy (IE = 4.92 ± 0.10 eV) and electrochemical investigations of the poly(TTh-C60) polarized in TBAP/DCM (IE = 5.01 ± 0.10 eV) and TBAP/PC solution (IE = 4.95 ± 0.10 eV) demonstrating good coincidence of the value. The electrochemical method revealed, that the location of the Fermi level relative to the valence and conduction bands indicates p-type character of semiconducting poly(TTh-C60). On the other hand photoemission spectroscopy manifests n-type behavior of examined sample. In turn, the UV-Vis result showed that the charge transfer (CT) between poly(TTh) and C60 unit can suggest, that these chromophores are not entirely independent.

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