Abstract
Tuning the sensing properties of spiropyrans (SPs), which are one of the photochromic molecules useful for colorimetric sensing, is important for efficient analysis, but their synthetic modification is not always simple. Herein, we introduce an alkyne-functionalized SP, the modification of which would be easily achieved via Cu-catalyzed azide-alkyne cycloaddition (“click reaction”). The alkyne-SP was conjugated with a bis(triethylene glycol)-benzyl group (EG-BtSP) or a simple benzyl group (BtSP), forming a triazole linkage from the click reaction. The effects of auxiliary groups to SP were tested on metal-ion sensing and cyanide detection. We found that EG-BtSP was more Ca2+-sensitive than BtSP in acetonitrile, which were thoroughly examined by a continuous variation method (Job plot) and UV-VIS titrations, followed by non-linear regression analysis. Although both SPs showed similar, selective responses to cyanide in a water/acetonitrile co-solvent, only EG-BtSP showed a dramatic color change when fabricated on paper, highlighting the important contributions of the auxiliary groups.
Highlights
A range of stimuli can induce closed forms of well-known photochromic molecules ie, spiropyrans (SPs), to undergo cis-trans isomerization to give rise to open-ring isomers or merocyanines (MCs) with vastly different physicochemical properties [1]
Shiraishi et al reported that a coumarin-conjugated spiropyran showed blue fluorescence after nucleophilic addition of CN− under UV light [5]
Since azide-containing molecules can be conjugated with alkyne-functionalized SP via
Summary
A range of stimuli (light, temperature, or metal ions) can induce closed forms of well-known photochromic molecules ie, spiropyrans (SPs), to undergo cis-trans isomerization to give rise to open-ring isomers or merocyanines (MCs) with vastly different physicochemical properties [1]. Such transformations of SPs enable their use as colorimetric sensors due to the vivid colors of the MC forms [2]. Stubing et al compared the absorbance and fluorescence spectra of methyl-1-aza-crown-functionalized SP with different sizes of the aza-crown moiety [6] These spectra showed the largest changes upon binding of Li+ (among alkali metal ions)
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