Crown Ether-Based Ion-Selective Organic Semiconductors by Molecular Design

This perspective highlights recent advances in the development of π-conjugated organic semiconductors with ion-selective motifs, with a particular focus on crown ether-functionalized small molecules and polymers that selectively recognize biologically relevant metal cations such as Na⁺, K⁺, and Ba²⁺. Through the utilization of the size complementarity between the crown ether cavity and target ions, various systems have been designed that show pronounced optical responses such as hypsochromic shifts, ratiometric absorption changes, fluorescence modulation, and aggregation-induced emission. Such properties can be ascribed to ion-induced conformational changes, π-conjugation modulation, and controlled intermolecular packing. Besides optical sensing, ion-selective interactions have been successfully utilized for the development of applications for electronic devices such as organic electrochemical transistors, wherein selective ion binding modulates charge transport in both p-type and n-type semiconductors. The incorporation of ion recognition motifs into π-conjugated backbones has made it possible to achieve selective dedoping, controlled aggregation, and large current modulation, thus proving the concept of ion-selective organic electronic devices. Moreover, the application of crown ethers has been shown to enhance processability, morphology, and electrochromic properties. These advancements demonstrate the growing importance of structurally modified organic semiconductors in adaptive electronics and bioelectronic sensing.