π‐Conjugated Polymer–Fullerene Covalent Hybrids via Ambient Conditions Diels–Alder Ligation

The established ability of graphitic carbon‐nanomaterials to undergo ambient condition Diels–Alder reactions with cyclopentadienyl (Cp) groups is herein employed to prepare fullerene‐polythiophene covalent hybrids with improved electron transfer and film forming characteristics. A novel precisely designed polythiophene (M _n 9.8 kD, Đ 1.4) with 17 mol% of Cp‐groups bearing repeat unit is prepared via Grignard metathesis polymerization. The UV/Vis absorption and fluorescence (λ_ex 450 nm) characteristics of polythiophene with pendant Cp‐groups (λ_max 447 nm, λ_e‐max 576 nm) are comparable to the reference poly(3‐hexylthiophene) (λ_max 450 nm, λ_e‐max 576 nm). The novel polythiophene with pendant Cp‐groups is capable of producing solvent‐stable free‐standing polythiophene films, and non‐solvent assisted self‐assemblies resulting in solvent‐stable nanoporous‐microstructures. ¹H‐NMR spectroscopy reveals an efficient reaction of the pendant Cp‐groups with C₆₀. The UV/Vis spectroscopic analyses of solution and thin films of the covalent and physical hybrids disclose closer donor‐acceptor packing in the case of covalent hybrids. AFM images evidence that the covalent hybrids form smooth films with finer lamellar‐organization. The effect is particularly remarkable in the case of poorly soluble C₆₀. A significant enhancement in photo‐voltage is observed for all devices constituted of covalent hybrids, highlighting novel avenues to developing efficient electron donor‐acceptor combinations for light harvesting systems.