Decoding Molecular Conformations of Dimeric Non-Fullerene Acceptors for High-Sensitivity Near-Infrared Organic...

The molecular conformation and packing behavior of dimeric non-fullerene acceptors (NFAs) remain largely unexplored, limiting their rational design for optoelectronic applications. Here, we report the first single-crystal structures of two imidazole-based dimeric NFAs, revealing well-defined intramolecular π-π stacking and compact molecular packing in the monomolecular state. These structural features lead to shorter π-π stacking distances and enhanced electronic coupling compared to their monomeric counterpart, resulting in improved charge carrier mobility and photoresponse. By varying the length of the alkyl linker, we tailor the optoelectronic properties and suppress the dark current in organic photodetectors (OPDs), enhancing both external quantum efficiency and specific detectivity. Devices based on the C8-linked dimer (H2-C8) achieve a peak detectivity (D_sh ^*) of 2.1 × 10¹⁴ Jones at 880 nm, and maintain values above 3.3 × 10¹³ Jones across 340-960 nm with an ultra-fast photoresponse time of 1.94 (t_rise) and 2.11 (t_fall) µs. These figures of merit place H2-C8 among the best-performing self-powered near-infrared OPDs, with performance on par with commercial silicon photodiodes. Our findings provide direct structural insights into dimeric NFAs and establish a new design pathway for high-performance organic optoelectronic materials.