Diaryl-ethenes

Masahiro Irie received his B.S. and M.S. degrees from Kyoto University and his Ph.D. in radiation chemistry from Osaka University. He joined Hokkaido University as a research associate in 1968 and started his research on photochemistry. In 1973 he moved to Osaka University and developed various types of photoresponsive polymers. In 1988 he was appointed Professor at Kyushu University. In the middle of the 1980 s he invented a new class of photochromic molecules - diaryl-ethenes - which undergo thermally irreversible and fatigue resistant photochromic reactions. He is currently interested in developing singlecrystalline photochromism of the diarylethene derivatives. 

Hereafter, a and b indicate the closed- and open-ring form isomers, respectively. The photocyclization and cycloreversion quantum yields were determined to be 0.46 and 0.015, respectively.1121 In the absence of oxygen, the coloration/decoloration cycle could be repeated more than 2000 times.[13] The basic performance of diaryl-ethenes is described below. 

A reversible photocyclization forms the basis for molecular switches with the diaryl-ethene structure (Scheme 11)J37- Irradiation of the colorless, nonconjugated, open form 24a with UV light results in ring-closure to the colored, conjugated form 24b. With visible light, the process can be reversed. 

One example is the formation of helicenes by dehydrocyclization of diaryl ethenes (Scheme 7), which was well investigated by the groups of Calvin and Kagan [110-114]. 

Professor at Kyushu University. In the middle of the 1980 s he H invented a new class of photochromic molecules - diaryl-ethenes - which undergo thermally irreversible and fatigue resistant photochromic reactions. He is currently interested in developing singlecrystalline photochromism of the diarylethene derivatives. 

Very few asymmetric [4+2] photocycloadditions have been described in the literature [11]. However, reported examples are usually found to proceed with good levels of selectivity. The intramolecular [4+2] photocycloaddition of the diaryl-ethene derivative (114) was found to proceed smoothly with good diastereoselec-tivity (de = 86.6% in toluene at -40 C) (Scheme 27) [155]. When the dielectric constant was increased slightly, the de was found to increase this was also the case as the temperature was lowered. The mechanism of the asymmetric induction is described in detail. 

The Dithienylethene System and Related Compounds. The area of diaryl-ethenes has been the subjeet of a review.Calculations have been carried out dealing with the photochromism of such compounds.A description of the preparation of diarylethene nanoparticles has been published, and a decrease in photocyclization was attributed to aggregation. Some novel photochromic diarylethenes have been synthesized. The photochemistry exhibited by these compounds suggests that they could be of use as optical switches.Tian and Yang have reviewed the area of diarylethene photochromic switches. 1,2-Bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene is at the basis of a new photochromic liquid crystal system. Yokoyama and his co-workers have patented details for such photochromic materials." ... 

A class of substances which fulfills these conditions are the fulgides (Fig. 12.2). Equally useful and frequently investigated are the diaryl-ethenes and the dithienyl-ethenes (Fig. 12.3) and similar molecules. In both cases, the photochromism is based on a bonding isomerisation. Here, a tt bond is transformed into a a bond, accompanied by a ring closure. This leads in solution to a new absorption line... 

Electrocyclization - helicenes. Brief cover reviews of the synthesis of helicenes were published.In the formation of helicenes and substituted phenanthrenes via the photochemical electrocyclization of diaryl-ethenes in the presence of iodine as an oxidant, the addition of THF... 

The preparation of substituted diaryl-ethenes, stilbenes, and analogues (e.g., stilbazoles) has been achieved by Wittig [45] or Homer-Emmons reactions [46] of substituted benzaldehydes and benzyl-triphenylphosphonium halides or benzyl-diethoxyphosphonates (see Scheme 4). 4-Methylpicolinium salts [96a,b] or 4-meth-ylpicoline-A-oxides [96c], upon reaction with benzaldehydes under basic conditions lead directly to the corresponding stilbazo-lium salts or stilbazole-TZ-oxides, respectively. As of late, the metal-catalysed cross-... 

Helicenes. A systematic investigation of chemically induced asymmetric photosyntheses of helicenes has led to the preparation of hexahelicenes (415) from the 1,2-diaryl-ethenes (416) the bridged helicene (417) has been obtained from the heptahelicene diester (418) by standard reactions. 

The 1,1-diaryl-2,2-difluorocthane derivative (2.2g) and 2% ethanolic KOH (60 mL) were heated under reflux for 2.5 h. Then, the alcohol was evaporated under reduced pressure and the residue repeatedly extracted with Et20. The combined ethereal solutions were washed with H20 and dried (MgS04). The Et,() was evaporated, and the colorless oil thus obtained distilled under reduced pressure. Recrystallization (MeOH) gave the ethene derivatives summarized in Table 5. 

Alkyl phenyl telluriums and diaryl telluriums react with Grignard reagents in THF or diethyl ether in the presence of catalytic amounts of nickel- or cobalt-phosphane complexes. Tellurium is precipitated. The organic groups combine to form in most cases all three possible coupling products in ratios determined by reaction conditions . The reaction of ( Z,)-phenylethenyl phenyl tellurium and phenyl magnesium bromide formed almost exclusively ( Zj-stilbene in quantitative yield. ( ZJ-Ethoxycarbonylethenyl phenyl tellurium and phenyl magnesium bromide reacted differently ( Fj-ethoxycarbonyl-(phenyl)-ethene and diphenyl tellurium were produced. Tellurium was not formed. ... 

Novel 2,6-DiarYl-Substituted Diimine Catalysts 39 Tab. 2.4 Ethene polymerization reactions with 6c after hydrogen addition. ... 

The tosyl group could alternatively be eliminated during the reaction when a base, such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU), was present, as is the case for the photolysis of 1,2-diaryl-l-tosylstilbenes that led to phenanthrenes or their heterocyclic analogues in one step (Scheme 14.15, path h). These results were consistent with a mechanism involving a base-induced ehmination of p-toluene-sulfinic acid from 9-tosyl-4a,4b-dihydrophenanthrene as intermediate, formed by photochemical cyclization of the starting ethene [88]. 

Tadros etal. reported the dimerization of l-bromo-2,2-bis(p-methoxyphenyl)ethene in acetic acid under sunlight irradiation. However, recent reports concerning this type of compound, l,l-diaryl-2-haloethenes, present a more complex reaction system with several processes taking place such as hydrogen abstraction, rearrangement, dimerization, and capture of the solvent. 

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