Synthesis and characterization of a novel poly(isothianaphthene)–C₆₀ double-cable polymer

A novel poly(isothianaphthene) (PITN)–fullerene (C₆₀) donor–acceptor double-cable polymer soluble in organic solvents is synthesized by a Friedel–Crafts arylation reaction using anhydrous FeCl₃ as the Lewis acid catalyst. The covalent attachment of C₆₀ to PITN has been primarily confirmed by the presence of fullerene skeletal hydrogen at 4.2 ppm in ¹H nuclear magnetic resonance spectrum and a vibrational band at 2856 cm⁻¹ corresponding to the C–H stretching frequency of C₆₀ in the Fourier transform-infrared spectrum. Based on the results of the elemental analysis, the synthesized PITN–C₆₀ double-cable polymer is inferred to have one C₆₀ molecule covalently bound to a trimer of isothianaphthene corresponding to a fullerene content of 64.51 wt%. The UV–visible spectral data indicate that the PITN–C₆₀ retains the electronic properties of both PITN and C₆₀. Density functional theory calculations have been carried out to establish the localization of frontier orbitals in PITN–C₆₀. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of PITN–C₆₀ are obtained as −4.82 and −3.44 eV respectively. The absence of interaction between PITN and C₆₀ in the ground state was ascertained by cyclic voltammetry. Investigation on the photophysical properties of the fullerenated polymer by photoluminescence technique confirms the occurrence of photoinduced electron transfer from PITN to C₆₀. The positioning of energy levels and effective luminescence quenching suggest that PITN–C₆₀ is a viable material for a molecular heterojunction solar cell.