Conjugated polymers from acenaphthene imide and acenaphthylene imide: significant modulation of optoelectronic properties by different fused-pentagon rings

Abstract

A novel family of π-extended strong acceptor units, i.e., dibrominated acenaphthene imide derivatives (ANI-2Br), are synthesized by dehydrogenation of the saturated fused-pentagon rings in dibrominated acenaphthylene imide precursors (AI-2Br). With an unsaturated fused-pentagon ring, ANI-2Br is a 12 π-electron non-alternant conjugated system, featuring a remarkable extension of light absorption and π-conjugation compared to its alternant conjugated precursor AI-2Br (a 10 π-electron system). ANI-2Br exhibits a low-lying LUMO at −3.89 eV, showing a very high electron deficiency that surpasses that of most previously reported aromatic mono-imide acceptor motifs. Furthermore, we explore their application in the construction of electron-transporting polymers by alternative embedding of ANI or AI motifs with bithiazole derivatives (P1 and P2) or the thiophene-flanked diketopyrrolopyrrole derivatives (P3 and P4). Notably, the backbone configurations and optoelectronic properties of the resulting polymers can be significantly modulated by different fused-pentagon rings in ANI and AI motifs. Despite the small structural variation from AI to ANI, the copolymers incorporating strong ANI acceptor units exhibit significant differences compared to the analogous AI-based copolymers, including extended absorption band, narrowed bandgap, deep-positioned LUMO (approaching −3.91 eV), and improved carrier mobility. Charge-transport polarities varying from p-type to ambipolar and ultimately to n-type behavior are demonstrated for their film field-effect transistor devices. Among them, the best-performing polymer (P4) shows the highest electron mobility of 0.08 cm² V⁻¹ s⁻¹. The results indicate that dehydrogenation-oxidation of the annulated pentagon rings in the AI and its derivatives is an effective strategy for creating non-alternant conjugated, strong acceptors and their structurally derived conjugated polymers, offering a new route to regulate their optoelectronic properties by different fused pentagon rings.