Thermal isomerization of spiropyran to merocyanine in aqueous media and its application to colorimetric temperature indication

Abstract

Thermally-induced isomerization of spiropyran derivatives in aqueous media has been studied. The colorless spirocyclic (SP) forms of spiropyran derivatives are isomerized to colored merocyanine (MC) forms even in dark conditions at elevated temperature. Equilibrium, kinetic, and deuterium experiments reveal that the thermal SP → MC isomerization is due to the stabilization of MC form by a hydrogen bonding interaction with water molecules. This leads to the ground state energy of the MC form decreasing to lower than that of the SP form, resulting in SP → MC isomerization. The thermal isomerization property is applicable to a rough indication of solution temperature. The spiropyran derivatives, when dissolved in aqueous media under irradiation of visible light with an appropriate light intensity, demonstrate an increase in MC absorbance with a rise in temperature. The absorption response occurs reversibly regardless of the heating/cooling sequence. The spiropyran derivatives therefore have a potential for colorimetric temperature indication.

Hydrochromic molecular switches for water-jet rewritable paper

“…4), the absorption band associated with the 1 O at 588 nm gradually diminishes with the same isosbestic point. The microenvironment with multi-molecular hydrogen-bonding networks 27,28 plays an important role for this water-induced switching phenomenon from 1 C to 1 O , which was demonstrated by the fact that an equilibrium of both 1 C and 1 O coexsits also in some other protic solvents-that is, methanol and ethylene glycol (see Supplementary Fig. 5, Supplementary Table 1 and Supplementary Discussion).…”

“…Inspired by the literature 27-31 studying solvation effects on the isomerization of some spiropyrans in aqueous solutions, we conjectured that the spiropyrans and related molecular switches could be potential hydrochromic dyes. By reviewing existing solvatochromic results of spiropyrans and related molecular switches reported so far, one critical problem preventing them being used practically is the colour instability under ambient light [27][28][29] . This might be due to unfavourable conjugated push-pull zwitterionic structure of their merocyanine isomers, which readily undergoes the ring-closing reaction under visible light.…”

“…11-13 were synthesized 33,34 according to the work reported by F. M. Raymo's group and us. 14-18 were synthesized and purified according to literature 27,35,36 . The detailed synthesis and characterization information for 1-18 was supplied in Supplementary Methods.…”

Reversible Multistimuli‐Response Fluorescent Switch Based on Tetraphenylethene–Spiropyran Molecules

“…[1] Up to now, various stimuli, such as UV/Vis light, [1,2] acid/base, [3] heat, [4] electricity, [5] and mechanoforce [6] all have been reported to accelerate this CF-OF transformation. Due to their excellent stimuli-response properties, spiropyrans have been widely studied for use in data storage, [7] chemical sensors, [8] smart materials, [9] and biological imaging [10] etc.…”

Spiropyran–Amidine: A Molecular Canary for Visual Detection of Carbon Dioxide Gas

“…Previous reports demonstrated that thermal SP!MC isomerisation of spiropyran can occur in aqueous media, even in the dark; this is attributed to the stabilisation of the MC form via a hydrogen bond interaction with water molecules. [23] Under the same conditions, the (1 and 2). The values in parentheses are the pH measurements at complete colour change.…”