Guest-conditioned multicolor writing on cellulose nanocrystal canvases

Abstract

Supramolecular smart paper has been created by embedding ionic macrocycles within cellulose nanocrystal films. The films can be written on with inks composed of colourless π-electron-rich molecules to reveal colourful, rewriteable patterns.

Self-Assembled Gels of Cellulose Nanocrystals for Diffusion-Controlled Color Switching

“…Guests Gp2 and Gn2 have phenylene and naphthalene cores, respectively, and two ethylene oxide units on their side arms; both Gp2 and Gn2 can form distinctive, colorful host−guest complexes in solution and in the gel states upon binding with CBPQT 4+ . 33 Gp2 and Gn2 show almost identical hydrodynamic radii (R H = 0.44 and 0.46 nm, respectively; see Table S2). Their different π-electron character, however, differentiates the self-assembly properties of Gp2 and Gn2 with CBPQT 4+ .…”

“…The chemical shifts for the aromatic signals matched well with those reported for compounds Gn2 (Figure S5) and Gp2. 33 This suggested that the aromatic cores retained their electron-rich character, which is important for their self-assembly with CBPQT 4+ .…”

“…The viologen protons a, b, and d split into two sets of resonances due to a slow rocking of the naphthalene core within the host, which breaks the symmetry of CBPQT 4+ ; this phenomenon has been previously demonstrated for naphthalene-containing guests. 33 The guest protons shifted drastically, e.g., proton H3 showed a 4.52 ppm upfield displacement, indicative of strong π-stacking interactions with the host (Figure 3c). All changes observed by 1 H NMR spectroscopy were consistent with those identified for the smaller analogue, Gn2, and indicated the formation of an inclusion complex with CBPQT 4+ .…”

“…In previous studies, we demonstrated that an in-film guest trading process would be possible based on the different stability of the host−guest complexes. 33 For example, according to their solution K a , when a film loaded with Gp2 ⊂ CBPQT 4+ was submerged in a solution of Gn2, Gn2 could easily displace Gp2 from the host cavity (because K a of Gn2 ≫ K a of Gp2) and turn the film from orange to purple. Since both are small molecules and have a high diffusion rate, it could be hypothesized that a film would show purple even if it was submerged in a solution containing Gp2 and Gn2 in equimolar concentrations (Figure 5a).…”

“…The same process was also achievable in CNC-CBPQT 4+ films. 33 While we have thoroughly studied the effect of the guests' core on defining the color of the in-gel complexes, 33 the impact of the lateral glycol chains on the guests has been overlooked. In principle, elongation of the lateral chains on the guest may increase the size of the guest and slow down its diffusion within CNC-CBPQT 4+ materials.…”