Terminal Hydroxylated Side‐Chains Enhance Ionic‐Electronic Coupling Efficiency in Small‐Molecule Semiconductors

ABSTRACT Small‐molecule semiconductors play a crucial role in organic electronics. However, when employed as organic mixed ionic‐electronic conductors (OMIECs), their limited ionic transport capabilities will obstruct efficient ionic‐electronic coupling. To address this issue, we propose a universal strategy by introducing terminal hydroxylated ethylene glycol (EG‐OH) side chains onto small‐molecule semiconductors. The 4Cl‐PDI‐EG‐OH, synthesized using this strategy, exhibits higher transconductance, faster response time, and better stability than the common ethylene glycol (EG)‐based 4Cl‐PDI‐EG in organic electrochemical transistors (OECTs). X‐ray single‐crystal diffraction and spectroscopic studies reveal that the terminal hydroxyl interlocking promotes the formation of ordered side‐chain arrangements, broadening the ionic transport channels. Concurrently, this induces the formation of short‐range charge‐transfer (CT)‐coupled J‐aggregates ( J CT ) within the backbones, maintaining efficient carrier mobility, thus achieving high‐efficiency ionic‐electronic coupling. Further applying this strategy to representative small‐molecule skeletons yields significant performance improvements. Specifically, BTP‐EG‐OH exhibits a remarkable transconductance of 101.9 mS, which is comparable to that of many high‐performance polymer‐based OECTs. This study shows that the EG‐OH side chain represents a superior choice compared to the currently common EG side chain for developing high‐performance small‐molecule OMIECs.