Ultrasound Stimulated Nucleation and Growth of a Dye Assembly into Extended Gel Nanostructures

A squaraine dye functionalized with a bulky trialkoxy phenyl moiety through a flexible diamide linkage ( GA‐SQ ) capable of undergoing self‐assembly has been synthesized and fully characterized. Rapid cooling of a hot solution of GA‐SQ to 0 °C results in self‐assembled precipitates consisting of two types of nanostructures, rings and ill‐defined short fibers. The application of ultrasound modifies the conditions for the supersaturation‐mediated nucleation, generating only one kind of nuclei and prompting the formation of crystalline fibrous structures, inducing gelation of solvent molecules. The unique self‐assembling behavior of GA‐SQ under ultrasound stimulus has been investigated in detail by using absorption, emission, FT‐IR, XRD, SEM, AFM and TEM techniques. These studies reveal a nucleation growth mechanism of the self‐assembled material, an aspect rarely scrutinized in the area of sonication‐induced gelation. Furthermore, in order to probe the effects of nanoscale substrates on the sonication‐induced self‐assembly, a minuscule amount of single‐walled carbon nanotubes was added, which leads to acceleration of the self‐assembly through a heterogeneous nucleation process that ultimately affords a supramolecular gel with nanotape‐like morphology. This study demonstrates that self‐assembly of functional dyes can be judiciously manipulated by an external stimulus and can be further controlled by the addition of carbon nanotubes.