Noncommutative Switching of Double Spiropyrans

Abstract

The spiropyran family of photochromes are key components in molecular-based responsive materials and devices, e.g., as multiphotochromes, covalently coupled dyads, triads, etc. This attention is in no small part due to the change in properties that accompany the switch between spiropyran and merocyanine forms. Although the spiropyran is a single structural isomer, the merocyanine form represents a family of isomers ( TTT , TTC , CCT , etc.) and protonation states. Combining two spiropyrans into one compound increases the number of possible structures dramatically and the interaction between the units determines, which are impeded due to intramolecular quenching of excited states. Here, we show that the coupling of two spiropyran photochromes through their phenol units yields favorable interactions (crosstalk) between the components that provides access to species inaccessible with the component monospiropyran alone. Specifically, the ring opening of one spiropyran unit, which is thermally stable at −30 °C, prevents ring opening of the second spiropyran unit. Furthermore, whereas protonated E - and Z -monomerocyanines were previously shown to undergo thermal- and photo-equilibration, the corresponding protonated E - and Z - bimerocyanines are thermally stable and show one-way photoisomerization from the Z , Z - to an emissive E , E -bimerocyanine form. Subsequent deprotonation at room temperature resets the system to the bispiro ring-closed form, but deprotonation at −30 °C yields the otherwise inaccessible bimerocyanine form. This form is photochemically inert but undergoes a two-step thermal relaxation via the merocyanine-spiropyran form, showing that the connection at the phenol units provides sufficient intramolecular interaction to fine-tune the complex isomerization pathways of spiropyrans and demonstrating noncommutability in photo- and pH-regulated multistep isomerization pathways.

5′-Substituted Indoline Spiropyrans: Synthesis and Applications

“…Symmetric 5 ,5 -dimer SP198 [106] and symmetric and non-symmetric 6,6-bis-SPdimers SP199-SP204 [122][123][124] in which fragments are linked by single C-C-bond were described. SP205 symmetric 5 ,5 -dimer SP-CH 2 -SP was synthesized [125].…”

Insights into extended coupled polymethines through the investigation of dual UV-to-NIR acidochromic switches based on heptamethine–oxonol dyes

“…[42][43][44] However, double-closure has been scarcely reported in the case of molecules that present two spiropyran moieties linked through a p-conjugated moiety. 41,[45][46][47][48][49][50] Herein, the variation of the heterocyclic end groups is useful to control the formation of the bis-spiropyran or to favour the zwitterionic species, while also tuning the optical properties in the NIR range. The different forms were explored by means of pH-dependent absorption spectrophotometric titrations and by studying their optical properties, which were supported by a theoretical investigation, providing a deeper insight into the structureproperty relationships in coupled polymethines.…”

Influence of Acid on Ring-Opening, Fluorescence, Aggregation, Electrochemical Oxidation, and C–C Bond Coupling of Spiropyran Derivatives

“…22 The open form normally has a positively charged N + atom in the indoline segment and a negatively charged phenolate in its zwitterionic structure. 23,24 The effect of acid on conventional spiropyran to yield protonated stabilized MC form and its application has been reported, 21,[25][26][27][28][29] but proton stabilized forms of benzothiazolinic spiropyran has not been investigated. The short-lived stereoisomers of the open form do not allow their detection using NMR techniques.…”