Biimidazole containing

The phototropic biimidazole containing one mole of yp water per mole of compound analyzed as follows ... 

One day in 1962, MacLachlan called me and said he had an idea, which he had demonstrated, but he did not know how stable the solution he had prepared was—so hurry. I mshed to his lab, and he showed me that he had dipped a filter paper in a solution that contained a biimidazole, a triphenylmethane leucodye, phenanthrenequinone, and Carbowax. He exposed it with a flashgun through a UV-blocking filter and a stencil and was able to bleach out the yellow color, to give a near white pattern. 

A number of tetraazafulvalenes 77 containing a p-quinoid substructure have been synthesized they include phenylogous biimidazoles such as 1,4-... 

A method was devised to determine extinction coefficients of radicals. A flash photolysis unit with filters to confine irradiation to a spectral region where only biimidazoles absorbed was utilized to generate radicals whose initial absorbance was recorded photographically from an oscilloscope. In the same cell another solution was then photolyzed as above. This second solution contained an identical concentration of biimidazole to the first plus leuco Crystal Violet dye, tris-(4-dimethylamino-phenyl) methane, and toluenesulfonic acid. The absorbance of dye produced by oxidation of leuco dye by was observed at an unobstructed wavelength. The extinction of the dye at this wavelength in this medium was determined experimentally. The stoichiometry of radical attack on dye was and the quantum yield of this reaction under... 

The 2-phenyl group can contain up to four substituents, while the 4 and 5 phenyl groups can contain up to three substituents each. The radicals and the dimers are stable and form a photocbromic system, finding utility as components in sun shields or shades. They are prepared by oxidizing the corresponding substituted 2,4,5-triphenylimidazole to form the biimidazole, which is dark stable. 

It should be noted that where the preparative method involves realtively low temperatures and the biimidazole (dimer) is substantially insoluble in the reaction medium as in the above Hayashi et al. procedure, the product precipitates as formed. Sometimes the crude product comprises mixtures of biimidazoles and may contain one or more biimidazoles that are relatively easily dissociated by heat, such as, for example, the 4,4 -isonier. Such thermal instability is, in general, more readily apparent in the liquid, e.g. in solution, than in the soiid. Ihus whereas the solid dimer may be essentially uncolored, i.e. undissociated at room and ordinary storage temperatures, it may become extensively colored, i.e. dissociated to imidazolyl radicals, almost immediately on being dissolved in an inert solvent such as benzene. As the radicals in solntion are in equilibrium with all possible dimeric structures, in time, in the absence of exciting light radiation, the radical color fades as the radicals dimerize to biimidazoles that are not thermally dissociable at that temperature in the particular solvent used. In other words, on equilibration, the system tends to produce biimidazoles that are thermodynamically stable at the temperatures employed. Thus no matter which of the above methods is used to oxidize a particular imidazole, substantially the same dimeric product is obtained on recrystallization under the same conditions. The l,2 -lsomer is such a product, obtained under the conditions described in Example 1. 

In each case, there was obtained a mixture of biimidazoles which contained at least one other isomer in addition to the l,2 -isomer, including the 4,4 -isomer (thermally dissociable at room temperature in solution). 

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