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 × 10¹³ 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.