Side-Chain-Assisted Transition of Conjugated Polymers from a Semiconductor to Conductor and Comparison of Their NO<sub>2</sub> Sensing Characteristics
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We designed two different conjugated polymers (CPs) containing alkyl and ethylene glycol (EG) side chains on the thiadiazol quinoxaline-based backbone as a donor-acceptor (D-A) type chain configuration to investigate the effect of a side chain. PTQ-T with an alkyl side chain showed typical p-type semiconducting properties, whereas PTQ-TEG with an EG-based side chain exhibited electrically conductive behavior. Both CPs generated radical species owing to their strong D-A type conjugated structure; however, the spin density was much greater in PTQ-TEG. Upon application to a field-effect transistor sensor for PTQ-T and a resistive sensor for PTQ-TEG, PTQ-TEG exhibited a better NO2 detection capability with faster signal recovery characteristics than PTQ-T. The flexible side chains in PTQ-TEG have a higher potential to enlarge the free volume as well as improve NO2-affinity, promoting the diffusion of NO2 in and out of the PTQ-TEG film and resulting in better NO2 detection capabilities.