Stable Water Insoluble Radicals of 1,1'',1"'-tribenzyl[4,2'; 4',4'; 6',4''']quaterpyridinium Trichloride for Photochromic Films
The electron relay compound 1,1'',1"'-tribenzyl[4,2'; 4',4'; 6',4''']quaterpyridinium trichloride (R7B) can be chemically or electrochemically reduced to a blue species which is insoluble in water and stable against oxygen in contrast to that obtained by reduction of methyl viologen. The species has a radical electronic structure as confirmed by EPR. Electrochemical reduction of R7B on SnO2 coated glass leads to water insoluble films. The colour of these radicals is dependent on pH; they are colourless in acidic and blue in alkaline solutions, which is ascribed to the reversible formation of a protonated charge transfer radical complex. R7B shows strong fluorescence. Under UV illumination, the excited state of R7B is reductively quenched by electron donors leading to the blue radical. Immobilization of such a system on a solid substrate leads to remarkable persistence of the colour (keeping the photochemically reduced films of R7B in the dark gave no detectable changes after one year) which can be used for long time optical information storage.
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Document Type: Short Communication
Publication date: December 1, 2011
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