An easily accessible isospiropyran switch

Abstract

A distinct, modular and switchable isospiropyran can now be prepared in a single step from abundant starting materials. This discovery opens an avenue for developing novel dynamic materials with unique responsive and switchable characteristics.

One-Pot Aldol Cascade for the Preparation of Isospiropyrans, Flavylium Salts, and bis-Spiropyrans

“…Along these lines, we hypothesized a mechanism for the conversion of 5-bromo-2-hydroxyacetophenone into an isospiropyran product (Scheme 1B) with the flavylium as the key intermediate; 20 this mechanism was supported with an isolation of the flavylium intermediate and its X-ray characterization. 15 We believe that the excess of SiCl 4 serves to give Bronsted acid HCl and perhaps removes H 2 O from the equilibrium (via acidcatalyzed conversion of Si(OEt) 4 into silica) and thus drives the transformation toward completion. Possibly, silicon-based monomers or oligomers could also be assisting the condensations by bringing the reactants in a close proximity.…”

“…In light of the one-pot synthesis of bromo-isospiropyran in Figure 1B, 15 we began our study by exploring the reactivity of ohydroxyacetophenones 1−7 holding electron-withdrawing groups (EWGs) in positions 4 and 5 (∑σ = 0−1.52, Figure 2A). 21 For depicting the electronic nature of the substituents, we decided to use Hammett's σ m/p (R 1 , Figure 2A) and σ m /σ + (R 2 , Figure 2A) parameters 21 with a somewhat arbitrary assumption that the stability of the flavylium intermediate directs the reaction's outcome, but also a notion that the resonance form shown in Figure 2A dominates its electron distribution.…”

“…In this vein, acetonitrile formed an O−H•••N hydrogen bond (D = 2.851/2.852 Å and Θ = 165.59/ 169.19°), 22 while the phenol moiety remained fully conjugated (φ = 6.69−6.81°, Figure 2B,C) to the benzopyran ring. Interestingly, the observed solid-state structures are almost identical to the previously reported 17 crystallized with acetone, 15 albeit one of the acetone molecules adopted a different position in the crystal lattice.…”

“…The inability of examined derivatives 13 to stabilize the zwitterionic and opened form of the dyes, in addition to a rapid conversion of the photostationary into thermodynamic equilibrium states, 14 have likely contributed to a lack of interest in further examining these materials. 11 Recently, we reported 15 a facile one-pot preparation of a novel isospiropyran using 5-bromo-2-hydroxyacetophenone (Figure 1B). In the presence of SiCl 4 in anhydrous ethanol, three molecules of the starting ketone thus combined into the product.…”

Spiropyran Sulfonates for Photo- and pH-Responsive Air–Water Interfaces and Aqueous Foam

“…Therefore, foams are of scientific and industrial interest and many studies are dedicated to the understanding of their formation, their properties, stability and structure. In our work, we have investigated spiropyran and merocyanine surfactants 21,[37][38][39][40][41][42][43][44][45] which can undergo photochromic reactions and are applied as new photoswitchable and also pH-responsive building block that can be activated by light and pH stimuli. In fact, we present the first study that addresses these surfactants on a molecular level at the air-water interface and their use as a stabilizer for aqueous foam.…”