A new amorphous dithienocyclopentapyrene-benzothiadiazole (PyDT-BT) polymer with high-mobility and strong red light emission

Abstract

Due to the contradictory molecular design principles required to achieve both high mobility and strong luminescence, the development of polymer semiconductors that simultaneously possess these characteristics remains a significant challenge. To address this issue, the development of structurally innovative conjugated polymers is highly desired. Herein, two dithienocyclopentapyrene (PyDT) donor units with either centro- or axial-symmetry were designed and synthesized, and subsequently copolymerized with a benzothiadiazole (BT) acceptor to afford cs-PyDT-BT and as-PyDT-BT. The resulting polymers exhibit pronounced position- and molecular-weight-dependent characteristics. Specifically, cs-PyDT-BT displays low crystallinity and a nearly amorphous microstructure, yet achieves higher charge-carrier mobility and intense red emission (∼670 nm) relative to its counterpart as-PyDT-BT, which shows higher crystallinity, lower mobility, and a red-shifted emission (∼690 nm). Furthermore, the influence of molecular weight was systematically investigated for cs-PyDT-BT. As the molecular weight increased, the film-state photoluminescence quantum yield (PLQY) gradually decreased, with the maximum value reaching 22%, while the highest mobility of 1 cm² V⁻¹ s⁻¹ was obtained at a medium M_n of approximately 100 kDa. This molecular design strategy provides new insights for developing next-generation conjugated polymers that combine strong luminescence with high mobility, thereby advancing multifunctional integrated polymeric materials.