Photochromic pyran compounds
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United States of America Patent
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Jan 27, 2004
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Feb 7, 2002
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Jun 7, 2000
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Abstract
Photochromic pyran compounds and their use in synthetic resin objects of all types, especially for ophthalmic applications, particularly spiro compounds having a fluorene structure derived from naphthopyrans, which are known as spirofluorenopyrans. By introducing respectively only one strongly electron donating or withdrawing group at specific positions in the periphery of the pyran dye, photochromic compounds obtained which in the excited state are distinguished by an expanded color spectrum, while simulataneously offering comparably good bleaching rates and good durability.
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