Zinc Selective Interactions of Porphyrins Aid Conversion of Nanoaggregates into Luminescent Microstructures: Toward the Development of a Sensing Platform

Supramolecular polymerization of structurally designed porphyrins offers a versatile platform for the fabrication of functional materials with excellent photophysical and biological properties. Herein, we report the synthesis and photophysical investigations of a porphyrin derivative appended with four dipicolylamine units at its meso positions. The molecules in the presence of acid form uniformly sized spherical nanostructures that could effectively transform into large microstructures upon interaction with zinc ions. The interaction of the nanostructures is highly selective, thereby facilitating the development of an ultrasensitive zinc sensing probe, exhibiting a nanomolar limit of detection. The presence of the dipicolylamine units is necessary for the formation of highly luminescent zinc-bound aggregates formed through a synergistic effect of metal–ligand, electrostatic, π–π stacking, and hydrogen-bonding interactions. Distinct spectral changes observed upon zinc binding in the solid state facilitated the fabrication of a dipstick form of the probe that enabled ease of application. The judicious design strategy adopted for the formation of porphyrinic nanosystems provides newer physical insights into the supramolecular polymerization of porphyrins and opens avenues for the synthesis of similar molecular systems with functional properties.