Vinylene‐Bridge‐Mediated Isomeric Dimer Acceptors With Ultranarrow‐Bandgap for High‐Sensitivity Near‐Infrared Organic Photodetectors

The development of dimeric acceptors (DMAs) for near‐infrared optoelectronics is hindered by inherent structural limitations including compromised planarity and reduced conjugation, which lead to blue‐shifted absorption spectra. Herein, we develop two vinylene‐bridge‐mediated isomeric DMAs based on multi‐selenophene substitution, named DYSe‐4 and DYSe‐5, distinguished by the different spatial positions of vinylene bridges. The DYSe‐4 and DYSe‐5 demonstrate record‐narrow optical band gaps of 1.29 and 1.27 eV. Compared to DYSe‐4, DYSe‐5 demonstrates reduced dihedral distortion, improved stacking orderliness, and enhanced intermolecular interaction. Consequently, the PBDB‐T:DYSe‐5‐based rigid organic photodetector (OPD) achieves an ultralow dark current of 9.7 × 10 −11 A cm −2 and a peak specific detectivity ( D sh *) of 9.7 × 10 13 Jones at zero bias. The flexible counterpart exhibits a responsivity of 0.54 A W −1 at 870 nm, setting a new benchmark for flexible near‐infrared OPDs. Extending beyond conventional externally powered photoplethysmography, we further construct a transmission‐mode sensing platform by integrating a mechanoluminescence (ML) emitter with porcine skin tissue. This work not only achieves a further redshift in the absorption of DMAs and elucidates the structure‐property‐performance relationships of isomers but also establishes a foundational architecture for ML‐driven health monitoring systems that operate without external power sources.