Spiropyran, photochromic

In his excellent review,2 Krongauz has summarized the effects of polymer matrices on spiropyran photochromism as reported in papers appearing before... 

S. A. Krysanov and M. V Alfimov, Ultrafast formation of transients in spiropyran photochromism,... 

A very simple calix[6]arene-based molecular machine operated by intermolecular photoinduced proton transfer was realized by employing wheel 1, N-decyl pyridylpyridinium axle-like [IT]", that upon protonation could act as a viologen-type guest, and the spiropyran photochrome SP (Fig. 29.9) [33]. This latter component has been selected because its acid-base properties can be photocontroUed so that it can... 

For two-photon memories, a number of media types and reading mechanisms have been used (165). Generally, media comprise two photon-absorbing chromophores dissolved within a soHd polymer matrix. Suitable reversible photochromic dyes are, for example, spiropyrans. Although photochromic materials often suffer from photobleaching, as well as from instability leading to self-erasure, new materials and host environments are under development (172). Bacteriorhodopsin (BR) also has been proposed as a two-photon memory material. 

Photochromism Based on Electrocyclic Reactions. The most common general class of photochromic systems involves reversible electrocychc reactions. Within this general class, the most weU-studied compounds are the indolino spiropyrans and indolino spiroxa2ines. 

The nitro spiropyrans are susceptible to fatigue which has limited their appHcation. Indolino spiroxa2ines exhibit photochromism by way of a mechanism that is very similar to that of the spiropyrans. 

Photoinduced transformations of photochromes (spiropyrans, furan-derived fulgides, dithienylethenes) in polymers 98PAC2157. 

Spectral Transparence Starting from 230 nm R R Spiropyran Light-Induced Ring-Opening Reactions Photochromism ... 

When the substituent groups in the polyphosphazenes were azobenzene [719] or spiropyran [720] derivatives, photochromic polymers were obtained, showing reversible light-induced trans-cis isomerization or merocyanine formation, respectively. Only photocrosslinking processes by [2+2] photo-addition reactions to cyclobutane rings could be observed when the substituent groups on the phosphazene backbone were 4-hydroxycinnamates [721-723] or 4-hydroxychalcones [722-724]. 

The photochromism of the spiropyran depends on the structure of heterocyclic parts, the medium such as solvent or plastic films, temperature, and light energy. Though the actual mechanisms may be more complex, a simple photochromic behavior in the spiropyrans is illustrated in Scheme 1. Initially, a spiropyran is excited by photoirradiation, and then a cisoid isomer arises after dissociation of the C—O bond. Finally, the cisoid form changes to the thermodynamically stable transoid form. The equilibrium between the cisoid and transoid forms largely depends on the substituent groups. The reversal of the colored form to the colorless spiropyran occurs by thermal or photochemical energy. More detailed mechanisms will be described in Section 1.2.1.6. 

Comprehensive and important reviews on photochromism of spiropyrans have been published by Bertelson1 and Guglielmetti2 In the present chapter, general synthetic methods and physical properties of spiropyrans with special reference to leuco dyes will be described. The chapter is divided into the spirobenzopyran, spironaphthooxazine, and spirothiopyran and related compounds. 

Instead of metal chelation, an intramolecular hydrogen bonding between the oxygen atom of phenolate and a hydrogen atom of a carboxylic acid in the 8-position leads to stabilization of the colored form, such as compound 12.20,21 This spiropyran exhibits reversed photochromism, which means that thermally stable species change from the spiro form to the colored form, and thus the colorless form produced by photoirradiation soon converts to thermally stable colored form. 

Solid films of spiropyrans are important in optical data storage. Thin films of spirobenzopyran (1.0 (tm) have been prepared by vacuum deposition, and its reversible photochromism has been confirmed.39 The J-aggre-... 

Spirooxazine is an aza analogue of spiropyran in which the carbon atom at 3-position is replaced by a nitrogen atom. Historically, the photo-chromic phenomenon of spiroindolinooxazine derivatives was found after discovery of photochromic spiroindolinobenzopyran.72... 

Becker and Kolc first examined the photochromism of spiroindo-linobenzothiopyran 44, a thio analogue of spiroindolinobenzopyran (Scheme 19). The closed form of this spirobenzothiopyran is stable and the photocoloration is very slow, compared with spiropyrans.71... 

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. 

Photochromic FRET using as acceptors the photochromic compounds such as spiropyrans [36]. They have the ability to undergo a reversible transformation between two different structural forms in response to illumination at appropriate wavelengths. These forms may have different absorption (and in some cases,... 

In the following, a number of examples are presented with emphasis on how such amplified imaging device can be built in self-supporting polymer materials. The present photochromic compounds (azobenzene and spiropyran derivatives) are rather common and have been used many times in molecular assemblies without touching upon the concept of image amplification. The most recent references are given(4. - 6). 

A spiropyran compound bearing a pyridinium group and a long alkyl chain behaves as a surfactant. The components shown in Scheme 1 exhibit reverse photochromism in polar solvents. The colored merocyanine form is more stable than the spiropyran form in the dark. Upon photoirradiation at A>510 nm, the polar merocyanine form is converted to the hydrophobic spiropyran form so that the CMC (critical micelle concentration) of the surfactant decreases. Consequently, when the initial concentration is set between the CMC of the two forms, photoirradiation induces a sudden formation of micelles at a certain conversion to the spiropyran form corresponding to the CMC of the mixed micelle of the two forms. 

When the initial concentration of the merocyanine form is lower than the CMC of the spiropyran form, the change in surface tension is gradual all through the progression of photoreaction. The value of Ajjq/Acqq remains constant during photoirradiation. Unfortunately, reversibility of this photochromism is poor and the micelle formation/dissociation cycle deteriorates rapidly. 

Chapter 8, by Hobley et al., critically evaluates the existing mechanistic results, especially that of time-resolved investigations, on the photochromic process of spiropyrans and related system. The summary provided should be of great value in the development of these systems as photoswitches. 

The photochromic mechanism for the chromenes is very similar to that for spiropyrans given in Figure 1.1. Under the influence of UV the C-0 bond in the pyran ring is broken to give either the zwitterionic form or, more likely, the cis- and fran.y-quinoidal forms (Figure 1.6). Studies suggest that formation of the cis-quinoidal species occurs in picoseconds, followed by generation of the trans-form in nanoseconds. 

Photochromic systems that have been examined in both of these approaches include spiropyrans, spirooxazines, diarylethenes, dihydroindolizines and azoben-zenes. A schematic of a disk structure is shown in Figure 1.14. To produce the... 

It is possible to attach photochromic molecules onto naturally occurring receptors and enzymes and by so doing be able to photoregulate their binding and catalytic activities. These materials have the potential to be used as chemotherapeutic agents and biosensors, and as bioelectronic materials. In most of this work to date spiropyrans have been used as the photochromic element in the system. 

Spiropyrans, and spirooxazines, better known for their photochromic behaviour (see sections 1.22 and 1.23), also exhibit thermochromism. The ring opening to produce the highly coloured merocyanine form is induced by heating either the solid or... 

Naumov P, Yu P, Sakurai K (2008) Electronic tera-order stabilization of photoinduced metastable species structure of the photochromic product of spiropyran determined with in situ single crystal X-ray photodiffraction. J Phys Chem A 112 5810-5814... 

Photochromism of Spiropyrans. The reversible photochromism of spiro-pyrans has been exhaustively studied by Fischer and his colleagues58 and shown to be a reversible transformation between the spiropyran form A (colorless) and the merocyanine form B (colored). 

To explain their results obtained in the study of photochromism of 1,3,3-trimethylindolino-6-nitro-8-methoxybenzospiropyrane adsorbed on silicic acid, Balny et al.57 have proposed that energy transfer takes place between the singlet states of A (spiropyrane) and B (merocyanine form). 

---