Morphological Transitions of a Photoswitchable Aramid Amphiphile Nanostructure

Abstract

Self-assembly of small amphiphilic molecules in water can lead to nanostructures of varying geometries with pristine internal molecular organization. Here we introduce a photoswitchable aramid amphiphile (AA), designed to exhibit extensive hydrogen bonding and robust mechanical properties upon self-assembly, while containing a vinylnitrile group for photoinduced cis−trans isomerization. We demonstrate spontaneous self-assembly of the vinylnitrile-containing AA in water to form nanoribbons. Upon UV irradiation, trans-to-cis isomerizations occur concomitantly with a morphological transition from nanoribbons to nanotubes. The nanotube structure persists in water for over six months, stabilized by strong and collective intermolecular interactions. We demonstrate that the nanoribbonto-nanotube transition is reversible upon heating and that switching between states can be achieved repeatedly. Finally, we use electron microscopy to capture the transition and propose mechanisms for nanoribbon-to-nanotube rearrangement and vice versa. The stability and switchability of photoresponsive AA nanostructures make them viable for a range of future applications.

Effects of molecular flexibility and head group repulsion on aramid amphiphile self-assembly

“…3b, via a previously established mechanism. 16 At neutral pH, as shown in Fig. 3c and described previously, 14 compound 1 forms nanoribbons, and at high pH, where electrostatic repulsion is minimized, disordered planar aggregates are observed (Fig.…”

“…[11][12][13] One such design motif is the aramid amphiphile (AA), which produces unusually stable self-assembled nanostructures by incorporating aromatic amide (aramid) domains into the molecular structure. [14][15][16] The prototypical AA is composed of a charged head group, a triaramid structural domain, and a short aliphatic tail (Fig. 1).…”

Thermoreversible Polymorph Transitions in Supramolecular Polymers of Hydrogen‐Bonded Squaramides

“…Importantly, since supramolecular polymorphs exhibit different molecular packing, morphology, and/or properties, controlled polymorph transformations are of great interest to develop stimuli‐responsive systems. However, direct polymorph transitions are challenging to achieve, particularly in organic solvents where solvophobic effects are attenuated [22, 31–42] . Among the scarce non‐aqueous examples, a family of ester‐bisurea monomers has been reported that reversibly self‐assemble into three distinct hydrogen‐bonded (H‐bonded) fibrillar nanostructures depending on the temperature, which provide different viscosity to the solution [38–41] .…”

Controlled release of drug molecules by pillararene-modified nanosystems

“…Macrocyclic compounds, including cyclodextrin, 19 calixarene, 20 cucurbituril, 21 and most recently pillar[ n ]arenes, are considered as excellent hosts to construct host–guest nanosystems. 22–24 Due to their various properties and ability to self-assemble into supramolecular structures through non-covalent interactions, 25 these host–guest nanosystems play a vital role in the fields of controlled release, 26 nanotechnology, 27,28 materials chemistry, 29 artificial molecular machines and artificial ion channels. 30,31 Pillar[ n ]arenes are a type of macrocyclic host which were synthesized for the first time in 2008.…”