Pyrazole-Based Metallogels Showing an Unprecedented Colorimetric Ammonia Gas Sensing through Gel-to-Gel Transformation with a Rare Event of Time-Dependent Morphology Transformation

A series of novel pyrazole-based
bis- and tris-amide molecules
have been synthesized and characterized which were found to gel copper
chloride only among other first row transition metals or other copper
salts. All the gels have been thoroughly characterized using infrared
spectroscopy, UV–visible spectroscopy, scanning electron microscopy,
transmission electron microscopy, and rheological studies. The gels
were composed of an infinitely long nanofibrillar network which displayed
an interesting morphological transformation to nanoscale metal–organic
particles (NMOPs), further corroborated by microscopic techniques
and X-ray powder diffraction data. Although NMOPs, hybrid organic–inorganic
nanoparticles, are widely known for their immense applications in
the field of drug discovery and medicine, NMOP-based metallogels are
not so common. Furthermore, this is a very rare example, to the best
of our knowledge, in which such a transformation is observed in metallogelation.
Gel 3 shows another extremely rare and fascinating external
chemical stimuli responsive gel-to-gel transformation with a potential
application of colorimetric ammonia gas sensing.