A Highly Stable Diketopyrrolopyrrole (DPP) Polymer for Chemiresistive Sensors

A novel donor–acceptor (D‐A) conjugated polymer, poly[bis(2‐ethylhexyl)3‐(3′′,4′‐bis(dodecyloxy)‐[2,2′:5′,2′′‐terthiophen]‐5‐yl)‐1,4‐dioxo‐6‐(thiophen‐2‐yl)pyrrolo[3,4‐ c ]pyrrole‐2,5(1 H ,4 H )‐dicarboxylate] (PDEB), comprising an electron‐accepting carbamate side‐chain bearing thiophene‐flanked diketopyrrolopyrrole (DPPTh) and an electron‐donating 3,3′‐bis(dodecyloxy)‐2,2′‐bithiophene (C12‐BTO) is synthesized. The carbamate side‐chains in this polymer can be thermally removed at a moderate temperature, forming an insoluble polymer poly[3‐(3″,4′‐bis(dodecyloxy)‐[2,2′:5′,2″‐terthiophen]‐5‐yl)‐6‐(thiophen‐2‐yl)‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione] (PDNB) with high solvent resistance. PDNB has a high highest occupied molecular orbital energy level of −4.68 eV and a narrow band gap of 1.05 eV, which makes it dopable by HCl to form a stable conductive polymer PDNB:HCl with moderate conductivity of 0.24 S cm –1 . A chemiresistive sensor based on PDNB:HCl can distinguish ten common volatile organic liquids with unique current–time profiles under a low operation voltage of 1 V. Importantly, a single sensor can be used many times and remain functional over a long period of time in air, indicating its extraordinary operational and environmental stability. The results demonstrate that PDNB is a promising material for reusable chemiresistive sensors.