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

Graphical abstract: - Abstract: 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 (E_opt = 0.59 ± 0.03 eV), the transport energy band gap (E_gtrans = 1.17 ± 0.20 eV) and the exciton binding energy (E_b = 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