Diradicaloid Strategy for High‐Efficiency Photothermal Conversion and High‐Sensitivity Detection of Near Infrared Light

Abstract Organic molecules are promising near infrared (NIR) photothermal materials because of their structural flexibility and fine‐tuned properties. However, weak NIR absorption and strong fluorescence character lead to low photothermal conversion efficiency (PCE). Herein, NIR quinoidal diradicaloids are designed and synthesized by a heteroaromatic‐bridged Blatter radical strategy. Benefiting from the relatively planar framework and diradical character, these singlet diradicaloids exhibit strong and broad absorption in the NIR region (750–1100 nm) in both solution and aggregate states, which do not show any fluorescence. High PCE up to 71.4% is evaluated under 808 nm laser. On this basis, a NIR detector employing a blend of the diradicaloids and conductive ionic liquid is fabricated, yielding a remarkably high thermal response of 1100% at 0.5 W cm⁻². This work reveals that π‐conjugated diradicaloids are promising candidates for NIR detection.