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

Abstract

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.