Photochromic spirofluorenopyran compounds
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United States of America Patent
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Dec 18, 2001
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N/A
app pub date -
Apr 25, 2000
filing date -
May 29, 1998
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Abstract
Photochromic spirofluorenopyran compounds corresponding to the general formula (I): ##STR1## in which B, B', R.sub.1 to R.sub.4 and G have the meanings defined herein. The compounds of the invention are useful in the production of photochromic articles, particularly articles made of synthetic resin materials, and exhibit rapid darkening and brightening rates, as well as long useful service lives. By appropriate selection of substituents, it is possible to adjust the properties of the compounds such as absorption maxima (color), brightening rate, etc.
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