Versatile Thermochromic Supramolecular Materials Based on Competing Charge Transfer Interactions

Abstract

Stimuli-responsive supramolecular materials are of paramount importance for a broad range of applications. It is essential to impart versatility, sustainability, and scalability into these materials. Herein the authors report the design and synthesis of a new class of thermochromic supramolecular materials, which can easily be processed from water via a reversible sol-gel transition. The supramolecular materials are composed of a bis-bipyridinium acceptor, a π-electron-rich naphthalene derivative donor, and halogen counterions. Long helical nanofibers can be assembled in water, gelating at room temperature. Inked designs, thin films, and aerogels are solution-processed to exhibit thermochromic behavior based on competing π → π* and n → π* charge transfer interactions. By using different π-electron rich donors, and counterions, the authors demonstrate that both the color observed at room temperature and at high temperatures can be tailored. The results open up the door to develop novel amphiphile-based thermochromes with water processability and a large tunable color palette.

Bis‐Bipyridinium Gemini Surfactant‐Based Supramolecular Helical Fibers and Solid State Thermochromism

“…Both techniques confirmed the entangled fibrous morphology of the CT assemblies. Interestingly, much like the fibers assembled from a similar bis‐bipyridinium acceptor and a dihydroxynaphthalene‐based π‐electron‐rich donor previously reported, a racemic mixture of helical fibers with different handedness were clearly observed by SEM and TEM. The formation of chiral helical aggregates without the presence of a chiral molecular template most likely resulted from a “non‐topological symmetry breaking”, which manifests during the donor–acceptor complex formation and is subsequently amplified during self‐assembly, fiber growth, and fiber bundling .…”

Assembly and Chiral Memory Effects of Dynamic Macroscopic Supramolecular Helices

“…In a previous study, we developed a series of donor–acceptor supramolecular assemblies that can form nano‐ and meso‐scale fibers in aqueous solution . These materials were composed of two components: an amphiphilic π‐electron‐deficient bis‐bipyridinium‐based acceptor ( 1 ⋅4Br) and a π‐electron‐rich donor.…”

“…Higher concentrations of the donor and acceptor led to gelation of the aqueous solution, which was reversible under thermal treatment (Figure S2). The hydrogel matrix was comprised of highly‐entangled supramolecular fibers, similar to those formed by 1 ⋅4Br and other achiral donors . In contrast to the racemic amount of left‐handed (M) and right‐handed (P) helical fibers formed with achiral donors, a dominating presence of M helices was observed [Figure b (center) and c (top)] by scanning electron microscopy (SEM).…”

“…In ap revious study,w ed evelopedaseries of donor-acceptor supramolecular assemblies that can form nano-and mesoscale fibers in aqueous solution. [19] These materials were composed of two components:a na mphiphilic p-electron-deficient bis-bipyridinium-based acceptor (1·4Br) and a p-electron-rich donor.A lthough both the donor and the acceptor were achiral molecules, the resulting self-assembled fibers were helical, exhibiting ar acemic mixtureo fh andedness without any external chiral influence. In this study,ac hiral a-amino acid donor, [14d, 20] tryptophan (Trp), was exploited to direct the formation of enantiomerically pure self-assembled architectures (Figure 1a).…”

“…The hydrogel matrix was comprised of highly-entangled supramolecular fibers, similart ot hose formed by 1·4Br and other achiral donors. [19,22] In contrastt o the racemic amount of left-handed (M) and right-handed( P) helical fibers formed with achiral donors, ad ominating presence of Mh elices was observed [ Figure 1b Fiber-fiber bundling was observed by SEM (Figure 1c), in which multiple smallerf ibers merged and generated thicker ones while maintaining the original helicity, thus affording macroscopic enantiomerically pure heliceso fi ncreasing size. This bottom-up process was surprisingly efficient and robust, generating single-handed helices under aw ide range of processing conditions (drop-casting, spin-casting, precipitation,r ecrystallization, etc.).…”