Building Block Dependent Morphology Modulation of Cage Nanoparticles and Recognition of Nitroaromatics

Morphology of nanomaterials has a strong impact on their chemical/physical properties, and controlled synthesis of such materials with desirable morphology is a major challenge. This article presents the role of a building block in the morphology of organic cage particles. In this context, three organic cages (A(3)X(2), B3X2, and C3X2) were devised from triphenylamine-based dialdehydes (A-C) and a flexible triamine (X) by utilizing dynamic imine chemistry. All of the synthesized cages were characterized by various spectroscopic techniques, which suggested the formation of [3+ 2] assembled architectures. Though the cages are isostructural, structural variation in the aldehyde building blocks imparted by the incorporation of phenyl moieties into the triphenylamine core produces morphologically diverse cage particles, as indicated by SEM. The synthesized cages were found to be fluorescent; the reduced analogue of cage A(3)X(2) (A(3)X(2)(r)) was tested to explore its use as a chemosensor for the detection of nitroaromatic explosives. The experimental findings suggest high selectivity and sensitivity of A(3)X(2)(r) towards picric acid (PA) among the various nitroaromatics tested. A theoretical investigation of fluorescence quenching suggested that formation of a ground-state charge-transfer complex with a resonance energy-transfer (RET) process could be the main reason behind such selectivity of the cage towards PA.