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Photochromic imidazolium based ionic liquids based on spiropyran
Simon Coleman1, Robert Byrne, Nameer Alhashimy
1Biomedical Diagnostics Institute, National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland.
Physical Chemistry Chemical Physics : PCCP
|May 15, 2010
Summary
A new photoswitchable compound, SP(Im), integrated into ionic liquids shows a ten times faster thermal relaxation rate than standard spiropyrans. Covalent attachment influences ionic liquid properties without affecting conductivity or viscosity upon photoswitching.
Area of Science:
- Materials Science
- Physical Chemistry
- Supramolecular Chemistry
Background:
- Ionic liquids (ILs) possess unique nanostructured domains.
- Photoswitchable compounds like spiropyrans can exist in two forms: spiropyran (SP) and merocyanine (MC).
- Understanding the behavior of photoswitchable molecules within ILs is crucial for developing advanced materials.
Purpose of the Study:
- To synthesize and characterize a novel imidazolium benzospiropyran derivative, SP(Im).
- To investigate the stability and thermal relaxation rates of SP(Im) in various imidazolium-based ionic liquids.
- To determine the impact of covalently attaching SP(Im) to an ionic liquid cation on its physicochemical properties.
Main Methods:
- Synthesis of SP(Im) via alkylation of an imidazole to a photoswitchable compound.
- Characterization of SP(Im) in imidazolium-based ILs with varying cation side-chain lengths.
- Comparative analysis of SP(Im) with a standard spiropyran (BSP) regarding stability and thermal relaxation.
- Investigation of rheological and transport properties (ionic conductivity, viscosity) at higher concentrations.
Main Results:
- SP(Im) exhibits a thermal relaxation rate approximately ten times faster than BSP (13.9 x 10⁻³ s⁻¹ vs. 1.0 x 10⁻³ s⁻¹ in [C₆mIm][NTf₂]).
- Covalent attachment of SP(Im) integrates the photoswitchable moiety into the non-polar IL domains, unlike unbound BSP.
- Ionic conductivity decreased by up to 23% for SP(Im), with the effect increasing with cation side-chain length.
- Photoswitching of SP(Im) did not alter conductivity or viscosity, suggesting mobility is key to property control.
Conclusions:
- The covalent linkage of SP(Im) to the imidazolium cation enhances its integration into IL nanostructures, leading to faster thermal relaxation.
- The stabilization of the merocyanine form of BSP is influenced by IL charge and domain interactions, affecting its lifetime.
- The observed changes in ionic conductivity are attributed to the influence of the covalently attached photoswitchable group on IL structure and ion mobility.
- SP(Im) offers a promising route for developing photoswitchable ionic liquid systems where conductivity and viscosity are not compromised by light-induced changes.
