The HABI Literature

There is a considerable amount of literature dealing with hexaarylbiimidazoles (HABIs). References to these compounds were found in over 130 journal articles as shown in Chemical Abstracts (CA) there were about 1050 patents abstracted in Chemical Abstracts. Most significantly, a very large database exists in the issued (over 1200) and applied patents (over 500) that can be examined on the U.S. Patent and Trade Mark Office website. Several chapters in survey books describe various aspects of HABI Chemistry. 

Dessauer wrote a chapter The Invention of DYLUX Instant Access Imaging Materials and the Development of HABI Chemistry—A Personal History in Advances in Photochemistry, Vol. 28, editors D.C. Neckers, T Wolff and W.J. Jenks, Wiley-Interscience (2005). 

Dessauer and C.E. Looney described some aspects of HABI chemistry in a chapter Low Amplification Imaging Systems in Imaging Processes and Materials Neblette s Eighth Edition, Van Nostrand-Reinhard (1989). 

Koko Maeda, contributed a chapter Hexaarylbiimidazolyl The Choice Initiator for Photopolymers, History of Synthesis and Investigations of Photochemical Properties , and Yi Lin, Andong Liu, Alexander D. Trifunac and Vadim Krongauz c chapter Investigation of Electron Transfer Between Hexaarylbiimidazoles and a Visible Sensitizer in Krongauz and Trifunac s Processes in Photo-Reactive Polymers, Chapman Hall (1995). 

None of these treat the impact that HABI chemistry had on industrial photochemistry, nor do they go into much detail into the patent aspects of HABI based photooxidation, photopolymerization, phototackification and other reactions. Also of necessity, they do not go into much detail about the different compositions that are involved in making this chemistry happen. 

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The author had collected the patent literature diligently, and developed a spreadsheet. Regrettably, long chemical names are generally not searchable in the USPTO database. As a matter of fact, it is amazing how many synonyms for HABIs must be searched, I have identihed the terms that were searched, and the number of hits (Table 5.1). 

Many publications in the literature describe the technical aspects of hexaarylbi-imidzole (HABI) chemistry. The following is an attempt to put these and the reported patent literature into a historical perspective and to add my personal reflections about the times, the scientists, and the emotions that were involved. Although several publications preceded the DuPont work, I believe that it was work in industry that elucidated and commercialized products based on these unique compounds. 

An index of the importance of a chemical compound can be seen from how often it is cited in the literature, or more importantly, for industrial scientists, how often it is mentioned in patents. As can be seen in a later chapter, HABIs have seen a considerable growth in usage, with no sign of abatement, so many years after they were first described in the literature. 

A program to investigate various organic materials as photochromic components in automotive and architectural windows, initiated about 1958 at DuPont seriously examined hexaaryl-biimidazoles (HABIs), which had been reported in the literature [see Chapter 5]. These compounds were relatively easy to synthesize, by the route indicated below (Scheme 8.2). 

The Japanese patent literature contains even more published patent applications that mention HABI technology. However, under Japanese patent law, patent claims have a very narrow scope. Consequently, a whole series of related apphcations might be filed in Japan when only a single apphcation would be filed in the United States. In addition, in Japan patent applications are pubhshed at eighteen months but are not examined until the applicant requests examination and pays an examination fee. Examination formerly had to be requested within seven years of the filing date, since shortened to three years, or the application is considered abandoned. Examination is never requested for a large number of applications so they act as defensive pubhcations. 

As will be quite obvious to the reader, much of the literature of HABIs is reported in patents. DuPont s commercial success in this field rested initially on the Cescon patent. 

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