Photochromic applications

The chromene ring of spirobenzopyrans such as (168) and (169) is opened by treatment with mineral add and closed again by alkali — a reaction of potential importance in the thermochromic or photochromic application of such compounds (69T5995,74JOU1516). 

Valence tautomerism refers to the interconversion of isomers without any accompanying rearrangement including proton transfer. Heterocyclic examples are essentially electrocyclic reactions (Scheme 15). If one of the isomers is colored and the position of the equilibrium can be changed by heat or light, the heterocycles can have useful thermochromic or photochromic applications. 

In his position as Associate Director of Research and Development, Optical Products, Dr. Crano managed the entire photochromies research program. He led the team of scientists that synthesized and evaluated hundreds of candidate photochromic dyestuffs, and directed all of the product and process development involved in the various Transitions lenses. In addition, his responsibilities included R D on non-ophthalmic photochromic applications, and on other optical coatings and resins. 

The application of nonlinear optical recording techniques for reversible optical data storage based on the excitation of photochromic molecules by two-photon processes also has been described (154). 

Nonadiabatic transitions definitely play crucial roles for molecules to manifest various functions. The theory of nonadiabatic transition is very helpful not only to comprehend the mechanisms, but also to design new molecular functions and enhance their efficiencies. The photochromism that is expected to be applicable to molecular switches and memories is a good example [130]. Photoisomerization of retinal is well known to be a basic mechanism of vision. In these processes, the NT type of nonadiabatic transitions play essential roles. There must be many other similar examples. Utilization of the complete reflection phenomenon can also be another candidate, as discussed in Section V.C. In this section, the following two examples are cosidered (1) photochromism due to photoisomerization between cyclohexadiene (CHD) and hexatriene (HT) as an example of photoswitching molecular functions, and (2) hydrogen transmission through a five-membered carbon ring. 

The present photoelectrochemical deposition/dissolution method is applicable to reversible control of the particle size. A typical application taking advantage of the method is the multicolor photochromism. Additional applications include surface patterning and photoelectrochemical actuator. The patterning is possible by using a thiol-modified silver... 

Spironaphthooxazine 33 is commercially available as a photochromic compound. Due to its excellent lightfastness, many spironaphthooxazines have been synthesized and their photochromic properties have been investigated for industrial applications. Spironaphthooxazine is colorless (Xmax < 400 nm), and its photomerocyanine form mainly gives blue color. 

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. 

The first chapter of the book deals with leuco-spiropyrans and related spiro compounds, which constitute one of the classes of leuco compounds not of the redox type. Such materials are photochromic, and are of major technical importance. The author, Hiroyuki Nakazumi of the Department of Applied Chemistry at the University of Osaka Prefecture, is well known for his researches in functional dye chemistry, particularly photochromic materials, and he provides a very useful update of the field, covering mechanisms, synthesis, spectra and applications, together with a useful section on approaches to near-infrared absorbing photochromic dyes. 

The compound exists normally as the trans or ( )-isomer 21a. This molecule is essentially planar both in the solid state and in solution, although in the gas phase there is evidence that it deviates from planarity. When irradiated with UY light, the ( )-isomer undergoes conversion substantially into the cis or (Z)-isomer 21b which may be isolated as a pure compound. In darkness, the (Z)-isomer reverts thermally to the (F)-isomer which is thermodynamically more stable because of reduced steric congestion. Some early disperse dyes, which were relatively simple azobenzene derivatives introduced commercially initially for application to cellulose acetate fibres, were found to be prone to photochromism (formerly referred to as phototropy), a reversible light-induced colour change. C. I. Disperse Red 1 (22) is an example of a dye which has been observed, under certain circumstances, to give rise to this phenomenon. 

As for the relevant application, recently, a specific photochromic compound, 1,2-bis(2 -methyl-5 -phenyl-3 -thienyl)perfluorocyclopentene (BP-BTE), and the analogs of HBO, 2,5-bis(5,-0 rt-butyl-benzooxazol-2 -yl)hydroquinone (DHBO), were employed in the high-contrast, reversible, photochromic switching of fluorescence emission and its perfect nondestructive readout (Fig. 14). Due to the large... 

In addition to the biological properties of many of these compounds, certain ring systems are of interest for electronic applications (compound 43), as fluorescent dyes (compound 330), or as photochromic materials (Equation 121). 

QDs excited by single or multiple photons exhibit multixponen-tial decays, in our hands generally with two components of <10 and 10-25 ns. This property renders the nanoparticles useful reagents for the systematic modulation of emission via a technique we have denoted as photochromic FRET (pcFRET, Fig. 12.5 see [1, 2, 134]). The method was developed in order to circumvent inherent limitations in the quantitative determination of FRET in cells, particularly in imaging applications. We have classified pcFRET as a member of the family of so-called acceptor depletion methods [1, 2] due to the reversible change in the structure, and thus spectroscopic properties, of the photochromic compound (e.g., a diheteroarylethene) serving as the FRET acceptor. The key... 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

Optical lithography, in compound semiconductor processing, 22 193 Optically active citronellol, 24 506 Optically transparent porous gel-silica, 23 75, 76 Optical materials nonlinear, 17 442-460 second-order nonlinear, 17 444—453 third-order nonlinear, 17 453-457 Optical memory, photochromic material application, 6 602 Optical microscopy, 16 467-487 history of, 16 467-469 in kinetic studies, 14 622 liquid immersion, 15 186 Optical mode density, 14 849, 850-852 Optical multichannel analyzers (OMAs), 23 143... 

VIII. Further Applications Photochromic and Photorefractive Materials... 

VIII. FURTHER APPLICATIONS PHOTOCHROMIC AND PHOTOREFRACTIVE MATERIALS... 

---