Conjugated Semiconducting Polymer with Thymine Groups in the Side Chains: Charge Mobility Enhancement and Application for Selective Field-Effect Transistor Sensors toward CO and H2S

Conjugated polymers with both high charge mobilities and responsive functionality have received increasing attention because of their promising applications in organic electronic devices and chemo-/biosensors. We successfully incorporated thymine groups in the side chains of diketopyrrolopyrrole (DPP)-based conjugated polymer PDPP4T-T. Our studies reveal that thin films of PDPP4T-T exhibit improved crystallinity and higher charge mobility compared with analogous polymers with pure alkyl chains. This is attributed to the formation of H-bonding among thymine groups, which could strengthen interchain interactions and thus facilitate an ordered packing of polymer chains. Importantly, thin films of PDPP4T-T containing either Pd(II) or Hg(II) ions were successfully fabricated via air-water interface coordination reactions of thymine groups with ions. Thin-film field-effect transistors (FETs) of PDPP4T-T containing Pd(II) ions exhibit a sensitive and selective response toward CO even at a low concentration of 10 ppb. Such an FET-based CO sensor with high sensitivity and good selectivity is achieved for the first time by using polymeric semiconductors. Alternatively, FETs with PDPP4T-T-Hg(II) thin films can be utilized to detect H2S with good selectivity and high sensitivity (down to 1 ppb). Therefore, incorporating thymine groups into conjugated polymers can not only improve semiconducting mobilities but also endow semiconducting thin films with sensing functionality.