Enhanced Chemiresistive Sensor Performance through Superior Accessibility to Metal Complex Sites via Triptycene-Skeleton Coordination Nanosheets

Conventional chemiresistive sensors based on metal oxide semiconductors offer high sensitivity, fast response, and low cost. However, the requirement for high-temperature operation is a major issue. Recently, conductive π-conjugated coordination nanosheets composed of metal ions and π-conjugated planar ligands have attracted attention as active materials for chemiresistive sensors operating at room temperature (RT). However, their tendency toward multilayer formation, driven by strong interlayer interactions, impedes access to metal complexes (active sites), thereby reducing their performance. In this study, we synthesized a composite (NiHATT/CNT) consisting of a coordination nanosheet (composed of nickel ions and the triptycene-based three-branched ligand, 2,3,6,7,14,15-hexaaminotriptycene (HATT)) and a carbon nanotube (CNT). We evaluated the humidity response of the chemiresistive sensors using NiHATT/CNT as the active material. The introduction of the triptycene skeleton allowed the square-planar metal complexes to form perpendicular to the two-dimensional surface, thereby allowing analytes to easily access the active sites. Consequently, the NiHATT/CNT chemiresistive sensor exhibited a significantly greater response than the sensor using an active material consisting of a conventional coordination nanosheet with a planar π-conjugated ligand. This demonstrates that the chemical design that provides high accessibility to the metal complexes in NiHATT by introducing a triptycene skeleton enhances the sensing performance of the NiHATT/CNT composite.