The Beginnings of HABI Chemistry at DuPont

The discovery of a photochromic oxidation product of triphenylimidazole by Hayashi and Maeda [1] stimulated wide interest in hexaarylbiimidazole dimers. At that time, an effort to develop photochromic windows and related products was underway at the DuPont Company under the direction of Dr. George R. Coraor, and Hayashi and Maeda s work was examined and duplicated. Fortunately, this interest attracted several synthetic chemists who were eager to develop related compounds with superior properties, what ever these might be. Obviously, for the proposed application, there was a need for a large number of reversals, different colors from the purple of the parent radical and different speeds of photolysis and recombination. 

Cescon and Dessauer synthesized over 100 different biimidazoles, with the able assistance of Robert Jenkins and Edward Urban. 

The photolysis of the various dimers was carried out in a wide range of different solvent and solid media, including the conventional solvents as well as binders such as polyvinyl butyral, cellulose acetate butyrates, etc. Inevitably the photochromic behavior was relatively brief due to the fatigue reaction, which we found to give rise to the parent triaryUmidazoles. 

Cescon proposed the synthesis of a photochromic polymer, based on the imidazole derived from terephthaldehyde. A bisimidazole was indeed synthesized, but on oxidation gave a deep blue color, which was identified as the monomeric oxidation product. 

Dessauer was aware of a very stable triphenylmethane leucodye tris(/7-A,A-diethylamino-o-tolyl)methane, which had been considered for a commercial product for the important spirit duplicating market. It was found by Cescon and Dessauer that the leucodye salt could be easily oxidized to give a deep blue color in solution, and a deep blue print when the exposure was carried out on filter paper that had been immersed in a solution of these components. 

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