Self-assembled superstructures derived from suitably substituted phenanthro[9,10-d] imidazole-based Zn(ii)/Cd(ii) complexes for selective detection of acetone

Abstract

The design and development of smart materials in developing advanced sensing platforms for volatile organic compounds (VOCs) have attracted increasing attention. π-Conjugated small organic building blocks, which can self-assemble into well-ordered superstructures, offer multiple advantages of high surface area, unique optoelectronic properties, good chemical/thermal stability, and host–guest interaction ability, which make them appealing candidates for VOC sensing. However, the fabrication of stable and well-ordered self-assembled structures from π-conjugated building blocks with appreciable electrical properties and their successful employment in the selective detection of VOCs remains a challenge due to the non-specific interaction between monomers during self-assembly and with other existing VOCs during sensing, respectively. Herein, we have designed and synthesized three phenanthro[9,10-d] imidazole-based ligands; L1, L2, and L3 with three different hydroxy benzene analog substitutions at the 2-position and their corresponding Zn(II) and Cd(II) complexes followed by fabrication into well-ordered superstructures with discrete morphologies for the selective detection of acetone vapour by measuring the contact potential difference using the Scanning Kelvin Probe (SKP). Several experimental analyses suggest that a precise combination of the operative non-covalent interactions along with the metal–ligand interactions drive the overall self-assembly process of these metal coordinated π-conjugated probes and could lead to generation of well-ordered various superstructures. Surface photovoltage measurements using the SKP on the surfaces of films coated with superstructures derived from these metal complexes were carried out both in the dark and under UV (Ultra-Violet) illumination in the presence of different vapours of VOCs. As per the results, under UV illumination, the thin film fabricated with superstructures derived from Cd complexes ((L1)₂M, (L2)₂M and (L3)₂M; M = Cd(II)) exhibit higher sensitivity and selectivity towards acetone in comparison with Zn(II) complexes-based superstructures. Thus, these self-assembled structures generated by the metal complexes of these π-conjugated molecular probes may provide new insights into the fabrication of organic electronic devices for gas sensors.