ISSN:
1573-1111
Schlagwort(e):
Clay
;
smectite
;
montmorillonite
;
bentonite
;
catalyst
;
isomerization
;
photochromism
;
ring closure
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract Reversible light induced colour changes have been observed in a variety of organic and inorganic systems: the phenomenon is termed photochromism. Suitable materials have potential uses ranging from data storage to labelling. The fulgide α-2,5-dimethyl-3-furylethylidene (isopropylidene) succinic anhydride shows photochromic behaviour which is modified considerably when the fulgide is supported on a smectite clay. We have shown that Smectites cause a bathochromic shift in the fight absorption of the fulgide and the photochrome of 20 and 80 nm, respectively, relative to the values in hydrocarbon solution. Moreover, the clays catalyse several reactions on different timescales. (1) Z →E isomerization of the fulgide. This process is an acid catalysed interlayer reaction strongly sensitive to the presence of polar molecules even at low concentrations. The most effective catalysts were clays exchanged with trivalent interlayer cations, equilibrated at low relative humidity before use. In toluene, reflux reactions were complete in ≈ I hour. The procedure can be used in a preparative sense. (2) The ring closure reaction to give the photochrome (i.e.E →P). This is a surface (and interlayer) catalysed thermal reaction, taking of the order of a day in toluene reflux. The reaction does not depend to any great extent on the type of smectite used, nor, within reason, on any pretreatment of the clay. (3) The decomposition of the fulgide and photochrome. These reactions were found to be acid catalysed and gave at least four products. The reactions occur in the interlayer region of the clay, but at a rate slower than those listed above, taking months to reach levels at which products could be detected. Although the shifts in light absorption noted above are of potential interest in a range of applications, the chemical activity of the clay, and the resistance of the coloured form to bleaching when supported on the clay, make such usage unlikely.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01133505
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