Modulating the Performance of N-Type Organic Conductors through Cyano Substituent Regiochemistry

Abstract

Cyano groups are compact, polar, and electron-withdrawing moieties that have been extensively utilised to tune the physicochemical properties of pharmaceutical molecules. Moreover, they are inherent acceptors of electrons and hydrogen bonds. Thus, they are expected to exert an unprecedented influence on the characteristics of organic mixed ionic-electronic conductors (OMIECs). However, the regioisomeric effects of cyano substitution on the electron density distribution, swelling, and performance within OMIECs remain insufficiently understood. In this study, we exchange the substituent position of cyano groups in donor-acceptor OMIECs and investigate the structure-mixed conduction characteristics. As a result, increase in the product of μC* was determined to be approximately 8-fold and 22-fold increases for cyanated 2,2'-Bithiophene(2T) and 2,2'-(1,2-ethenediyl)bis-Thiophene(TVT)-based OMIECs. This comprehensive improvement is ascribed to the promoted hydrophilicity and electron-accepting capability of the comonomers. Electrostatic potential calculations reveal a more uniform distribution of negatively charged carriers along the backbone following comonomer substitution, suggesting a higher electrochemical reduction capacity upon its interaction with Na+ ions. Moreover, in situ UV–vis–NIR spectroscopy confirms charged-state formation, while grazing-incidence wide-angle X-ray scattering reveals expanded π–π stacking coherence lengths following doping. These findings establish cyano-substituent regiochemistry as a decisive parameter to boost ionic-electronic transport in n-type OMIECs.