Unveiling π–π interactions in triptycene-phenazine/SWCNT redox chemistry using ESR spectroscopy

Abstract

Grasping the intricate π–π interactions between redox-active organic materials and conductive carbons is key to optimizing the performance of organic electrodes in energy storage devices. However, their precise role in redox chemistry remains elusive. In this work, the geometric congruence between the triptycene-phenazine (Trip-Phz) molecule, with its paddle-wheel structure, and the curved single-walled carbon nanotubes (SWCNTs), enables the self-assembly of Trip-Phz/SWCNT composites for aqueous supercapacitors. The Trip-Phz/SWCNT composites demonstrate well-defined redox peaks on cyclic voltammograms, coupled with a specific capacitance of 410 F g⁻¹. Our study goes one step further by capturing the electrochemically induced radicals through electron spin resonance (ESR) spectroscopy. The theoretically predicted robust π–π interactions between the inner-layer Trip-PhzH₆³˙⁺ radicals and SWCNTs facilitate the electron transfer effect, leading to an ESR silent state. Conversely, the ESR spectra of the outer-layer radicals feature a Dysonian line, attributive of the high conductivity of the Trip-Phz/SWCNT composites (∼10² S cm⁻¹). The insights gained from this research inspire the design of stable organic/carbon electrodes for advanced energy storage devices.