N-Type Small-Molecule Semiconductors for Bioelectronic Applications

Organic electrochemical transistors (OECTs) have drawn tremendous attention in research communities all over the world due to their biocompatibility and synthetic tunability. In the last few years, molecular design has been playing an essential role in developing organic semiconductors for OECT devices. Previous research was mainly concentrated on the design of p-type materials for OECTs. Ever since a novel polymer comprising the naphthalene diimide (NDI) monomer was successfully designed and synthesized in 2016, considerable efforts have been devoted to developing novel n-type channel materials. The quick development of this field during the past few years can be attributed to the synthetic methods, various materials design strategies and device engineering protocols. With the emergence of novel molecules, detailed structure-property relationships of channel materials and reasons for their excellent performance should be explored further.<br/>The work I will present is about a series of n-type small-molecule semiconductors based on naphthalene diimide (NDI) and perylene diimide (PDI) building blocks. When functionalized with different ion-transporting groups at the imide nitrogen positions, such as different length linear and cyclic ethylene glycol motifs, mixed ionic-electronic conduction properties were observed for thin films in aqueous environment. The solubility and aggregation behavior of these organic mixed conductors can be modified without changing the optical and electrochemical properties of the π-systems. Besides, PDI functionalized with an ion-selective ethylene glycol moiety exhibited good ion doping of the thin film with markedly different behavior in sodium chloride and potassium chloride solution, which paves the way for ion-selective mixed conductors as promising materials in organic electrochemical transistors and biosensors.