Browsing by Author "Evans, RA"
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- ItemCO2 triggering and controlling orthogonally multiresponsive photochromic systems(American Chemical Society, 2010-08-11) Darwish, TA; Evans, RA; James, M; Malic, N; Triani, G; Hanley, TLWe report a new generic method of reversibly controlling the photochromism of spiropyrans. It was found that the photochromic effect of spiropyrans can be reversibly switched on and off by addition and removal of carbon dioxide (CO2) to spiropyran in alcohol solutions containing an amidine (i.e., DBU) that acts as a CO2 sensitizer. Spiropyrans are not photochromic in the presence of DBU but photochromic when CO2 is subsequently added to the solution. The CO2 is readily removed by inert gas bubbling, thus allowing facile activation and deactivation of the photochromic effect. Carbon dioxide, without the presence of the sensitizing amidine, had no effect on photochromism of the spiropyrans. Other photochromic dyes classes such as spirooxazines and chromenes are not affected by this CO2/DBU stimulus. As a result, orthogonal activation of mixtures of spirooxazines and spiropyrans was achieved to provide four color states (clear, yellow, green, and blue) by varying the combinations of the stimuli of UV, visible light, CO2, and CO2 depleted. This finding now permits the many applications using spiropyrans to be CO2 responsive. © 2010, American Chemical Society
- ItemPhotochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT.(American Chemical Society, 2010-05-07) Yee, LH; Hanley, TL; Evans, RA; Davis, TP; Ball, GEPhotochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers were monitored using NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation. NOESY and ROESY experiments reveal the TTC (trans−s-trans−cis) isomer to be the dominant merocyanine isomer formed on photolysis, with some CTC (cis−s-trans−cis) isomer also present. Significant ROE cross peaks were observed between the “bulk” of the oligomeric units and protons across the entire photochromic core of the molecule, the intensity of these cross peaks suggesting that the interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain. The 2D NMR spectra indicate that there is exchange between the TTC and CTC isomers even at 193 K. This isomerization of the parent spirooxazine compounds, lacking the oligomeric side chains, was found to be acid-catalyzed, and DFT calculations support the strong possibility that it is the protonated merocyanine form that undergoes the facile isomerization process. Interconversion of the different merocyanine isomers is suggested to be fast on the NMR time scale under many experimental conditions, precluding the observation of different isomers using NMR spectroscopy at room temperature. © 2010, American Chemical Society
- ItemSpiropyran, chromene and spirooxazine, mélange á trois: Molecular logic systems through selective and reversible deactivation of photochromism mediated by CO2 gas(Elsevier, 2012-02-01) Darwish, TA; Evans, RA; Hanley, TLWe report a new expanded molecular logic system based upon combinations of spiropyrans, spirooxazines and chromenes, whereby the photochromism of some molecules can be selectively preserved while reversibly deactivating the photochromism of others. The non-photochromic molecules can be reversibly activated by CO2 gas. It was found that the photochromic effect of spiropyrans, in general, and one spirooxazine (with a hydroxyl group on the naphtho-ring) could be reversibly deactivated by DBU, while a chromene and an unsubstituted spirooxazine remained photochromic in the system under the same conditions. The presence of protic solvent was necessary for the deactivation of some of these photochromic molecules and hence it was used as an additional sensitizer in the system. This afforded the expansion of stimuli for molecular logic operations and allowed combinations of the benign stimuli of UV, visible light, CO2, and CO2 depleted with protic and aprotic solvents. This effect provided the mechanism for molecular logic systems that do not suffer from the usual problems of dilution effects and hence become truly reversible. This is highly significant when designing molecular switches to perform logic operations. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
- ItemSpiropyran–amidine: a molecular canary for visual detection of carbon dioxide gas(Wiley-Blackwell, 2011-10-01) Darwish, TA; Evans, RA; James, M; Hanley, TL