Self-Assembled π-Conjugated Cu(II)–Phenanthro[9,10-d]imidazole Superstructures for VOC Sensing and Enhanced Supercapacitor Performance

Abstract

The development of self-assembled smart materials is a pivotal area of advanced research, particularly for sensing and electronic applications. π-Conjugated small organic molecules can self-assemble into well-ordered superstructures with remarkable optoelectronic, chemical, and structural properties, making them suitable for applications such as volatile organic compound (VOC) detection and energy storage in supercapacitors. However, the self-assembly behavior of Cu(II) complexes derived from π-conjugated ligands, and their potential use in areas such as health, environmental monitoring, and energy storage, remain underexplored. In this study, we designed and synthesized two π-conjugated phenanthro[9,10-d]imidazole-based ligands (S1 and S2) and their corresponding Cu(II) complexes, (S1)₂Cu and (S2)₂Cu. These complexes self-assemble into well-ordered superstructures with distinct morphologies and selectively detect acetone vapors via Scanning Kelvin Probe (SKP) measurements. Their properties are governed by multiple non-covalent interactions in combination with metal–ligand coordination, which control the shape and size of the assemblies. Surface photovoltage measurements under dark and UV conditions, in the presence of different VOC vapors, revealed that (S1)₂Cu exhibits superior selectivity toward acetone compared to (S2)₂Cu. The pseudo-capacitive performance of the self-assembled superstructures was also evaluated in 1.0 M KOH aqueous electrolyte, yielding specific capacitances of 230.0 F g⁻¹ for (S1)₂Cu and 195.0 F g⁻¹ for (S2)₂Cu. (S1)₂Cu also demonstrated higher rate capability and better capacitance retention (75% after 4000 cycles). Overall, this work presents a promising strategy for designing self-assembled superstructures from metal-coordinated π-conjugated systems as advanced functional materials for VOC sensing and potential electrode material for aqueous supercapacitor applications.