A Quinoidal J‐Aggregated Indacendiselenophene Exhibiting High Responsivity in Ultra‐Narrowband Organic Photodetection

Organic semiconductors that exhibit narrowband absorption in the near‐infrared (NIR) region are highly sought after for photodetector applications, yet achieving such behavior intrinsically remains a considerable challenge. We report a novel fused quinoidal tetracyanoindacenodiselenophene material (QIDSe‐C16) that forms solid‐state J‐aggregates producing a remarkably sharp absorption band with a full width at half‐maximum (FWHM) of 27 nm centred at 772 nm, closely matching that of its sulfur analogue (QIDT‐C16). Despite exhibiting similar optical and electrochemical characteristics, selenium substitution enhances charge‐carrier mobility and significantly improves device performance. Optimized organic phototransistors (OPTs) based on QIDSe‐C16 display ambipolar transport and excellent photoresponsivity, reaching 289 A W −1 at 780 nm illumination, which is an order of magnitude higher than QIDT‐C16‐based devices and among the best so‐far reported values. Our findings demonstrate that controlling solid‐state aggregation through heteroatom engineering offers an effective route to narrowband, filter‐free NIR photodetectors that combine spectral selectivity with high charge transport.