Self-assembled π-conjugated Cu(ii)–phenanthro[9,10- <i>d</i> ]imidazole superstructures for VOC sensing and enhanced supercapacitor performance

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-<i>d</i>]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 <i>via</i> 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 materials for aqueous supercapacitor applications.