Stilbene compounds, photochromic

The photochemical ring closure of certain stilbenes, eg, the highly methyl substituted compound (2) [108028-39-3], C22H2g, and their heterocycHc analogues is the basis for another class of photochromic compounds (31—33). 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

It was only recently that these phenomena were detected photochemically using photochromic molecules whose chromophores undergo a reversible photoisomerization reaction. The photochemical reactions involved in these processes are mainly the trans-ds isomerization of aromatic azo compounds and stilbene derivatives as well as the ring opening/dosure reaction of spirobenzopyran derivatives . ... 

Topics which have formed the subjects of reviews this year include theoretical studies of the photochemistry of thiiranes, photoaddition of amines to aryl olefins and arenes, the synthesis of heterocyclic compounds, photoamination directed towards the synthesis of heterocycles, selective addition of organic dichalcogenides to carbon-carbon unsaturated bonds, photocyclisation mechanisms of c/5-stilbene analogues, synthetic utility of the photocyclisation of aryl-and heteroarylpropenoic acids, photochromic diarylethenes, spiropyrans, cy-clophanes, and polycondensed aromatics," photochromic organic media, photophysics and photochemistry of P-carbolines, and the photochemical synthesis of macrocycles.Chirality switching by light has also been described. ... 

Cis trans photoisomerization of olefins has been reviewed repeatedly. Ross and Blanc [22] reported on photochromism of several classes of compounds containing C=C and N=N double bonds. Fischer [23,24] highlighted certain aspects of photochromism and reversible photoisomerization. Hammond [2] and his group put the understanding of the sensitized isomerization of stilbene on a firm basis. Saltiel et al. [25-28] presented several reviews about the mechanism of cis trans photoisomerization of 1,3-dienes, alkenes, and stilbenes. Mazzucato [29] compared the properties... 

Electron cyclizations of the cw-stilbene type can lead to highly coloured compounds that can be of some industrial value. A few examples of photochromism of this type with... 

Photoisomerization of azobenzenes has been widely developed as photochromic compounds. Lots of papers sriU appeared in this subject from basic chemisty to applications. Some examples were described. Harada et al., reported the effect of cyclodextrin derivatives bearing photo-isomerized stilbene moiety. Single molecule conductance of E- and Z-4, 4 -(ethane-l,2-diyl)dibenzoic acids (E-l and Z-1) was determined using scanning tunnelling microscopy (STM). The dynamics of photoisomerization of E- and Z-urocanic acids (E- and Z-2) driven by Hg-free... 

The dimesitylbotyl borepin (169) underwent [2 + 2] photocycloaddition to give (169). A cast firm of (169) from a toluene solution showed photochromic behaviour with a colour change from colourless to deep blue. On the other hand, the bis-boron bridged stilbene (170) upon 254 nm irradiation afforded the novel boron-containing heterocyclic compound (171). ... 

It has long been known that the stilbene-type photoq clization occurs readily with styryl-heteroarenes and 1,2-diheteroaryl ethenes. Such processes not only provide a convenient access to novel as well as known polynuclear heteroarenes, but also in the latter series of these photoactive compounds, have been widely researched for a number of years as photochromic systems that have potential for development as the key element in data storage devices and as molecular switches. ... 

The other common photo-induced initial step is the cis-trans isomerisation as in the case of stilbenes and azobenzenes. Scheme 2.3. Other systems consist of two steps, a cis-trans isomerisation followed by cyclization, as in diarylethenes. Scheme 2.4, and fulgides. Scheme 2.5. In the case of diarylethenes the photoisomerisation step is avoided by "freezing" the compound in its cis configuration through an appropriate structural modification. This prevents the initial isomerisation process and the photochromism is only controlled by the cyclization reaction. Scheme 2.4, bottom. [4]... 

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