Sunglasses, photochromic

The colored form of spironaphthopyran 32 absorbs at A,max of ca. 450 m,70 and the closed spiro form is colorless, which has no absorption band above 400nm. Bulky substituent group is especially important for photochromic sunglass. Introduction of the spiroadamantane or spirobi-cyclo[3.3.1]heptane into the 2-position of naphthopyran increases the resistance to photo-fatigue reaction, since endocyclic double bond induced by 1,7-hydrogen shift in the colored form cannot be formed in 2-adamantyl or 2-bicycloheptanyl group. 

Spirooxazine compounds are useful in the field of plastic lenses, such as sunglasses and ski goggles. The plastic photochromic sunglasses have been in the marketplace since the early 1980s, and their market share is presently ca. 70%. The excellent lightfastness of the spironaphthooxazine series makes such applications possible, compared to other photochromic compounds. 

Photochromic sunglasses should ideally be colourless under low-light conditions, be converted rapidly to a form with an appropriate absorption spectrum under intense light, and revert quickly to colourless under low light. All of this needs to happen efficiently over a wide temperature range and the system must be capable of an almost infinite number of cycles. 

At that time we became aware of photochromic sunglasses Lord and Taylor s (a New York City department store) offered some for around 16, and we bought a pair. But were not impressed with their performance. We thought that they employed some materials then available from American Cyanamid, which reported that they had photochromic materials for sale. We continued to dissolve HABIs in ever more purified solvents obtained from Paris and Sperati, and finally managed to fill some glass cells that actually lasted about 2 weeks,... 

Photochromic lenses are often used in prescription eyeglasses—eyeglasses that are worn to correct vision. Having photochromic lenses protects the eyes and, similar to sunglasses, shields the user from bright sunshine outdoors. Some prescription eyewear can be tinted like sunglasses. 

Obvious applications of photochromism include glasses which darken according to the intensity of the surrounding light, and such glasses have now been available for some time both in the form of plate glass for windows and in the form of lenses for sunglasses. Their action is very slow, it takes indeed many minutes for the photostationary state to be established. This is due to the fact that the photochromic effect takes place at the molecular level... 

One of the most widely used photochromic compounds for sunglasses is prepared easily as follows reaction of 2,7-dihydroxynaphthalene with a mixture of sodium nitrite and sulfuric acid... 

This experiment confirmed the fact that photochromic materials are beginning to find a broad range of applications that goes beyond their familiar use in sunglasses, windows, and other everyday devices. As researchers develop abetter understanding of the fundamental principles involved in the way photochromic materials operate, advanced applications in molecular switches, nanocomputers, and other nanometer-scale devices are likely to become much more common. 

Practical applications of photochromism at first (ca. 1955-70) concentrated on the spiropyrans, and especially on BIPS compounds, because of their ready availability, photosensitivity, convenient thermal fade rates, and good color contrast when perceived by the human eye. However, applications in which the dye was required to cycle very many times (e g., an optical binary switch for a photochemical computer memory) or be irradiated continuously (e g., sunglasses, vehicle windshields) were impractical because of the rapid fatigue of these dyes.196... 

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