2- perfluorocyclopentenes

Photochromic dithienyl- and dibenzothienylethenes, particularly those containing the central 1,2-perfluorocyclopentene fragment, belong to the major group of compounds, which have attracted the attention of researchers in the field of information storage (optical memory) and optical switches because their starting (A) and cyclic (B) forms are, in most cases. 

Abstract The review considers the synthesis and structures of photochromic products, in which hetaryl substituents are separated by the centtal 1,2-perfluorocyclopentene moiety. It was also briefly presented main methods for synthesis of octafluorocyclopentene and its reactivity. Among methods used for the synthesis of the photochromes, the reactions of hthium derivatives of thiophene, benzothiophene, and other heterocyclic compounds with octafluorocyclopentene, 1,2-dichlorohexafluorocyclopentene, and their analogues are described. Another general method for the synthesis of dihetarylethenes, considered in the review, is based on the McMurry reaction involving the initial... 

The synthesis and structures of the photochromic products in which the hetaryl substituents are separated by the central 1, 2-perfluorocyclopentene fragment are described in the present review. The first section briefly presents the main methods for the synthesis of perfluorocyclopentene and its reactivity that predetermines methods for the synthesis of photochromic dihetarylethenes. The second section directly deals with the methods for the synthesis of these photochromes, and spe-ciflc features of their structures are described in the third section. The photochromic properties of the products, for minor exceptions, are not considered. 

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... 

Here typical syntheses of symmetrical products are considered. In Scheme 2, the treatment of bromide 1 with butyllithium under standard conditions in the presence of perfluorocyclopentene affords photochrome 2 (31 %) (99IZV979). Derivatives 3 and 4 were synthesized in a similar way (98KGS927). 

Typical syntheses of unsymmetrical derivatives include 27 (98CL1123), 28 (08SA1065), and 29 (Scheme 10). The perfluorocyclopentene fragment in the latter compound is bound to different positions in the thiophene moieties (95CL969, 04CC1010). 

In addition to thiophenes, the above reactions of perfluorocyclopentene, as well as of fluorinated derivatives of cyclobutene and cyclohexene, can be carried out with fused thienyl derivatives and various heterocycles forming relatively stable anions. 

New macromolecules 99 and 100 can easily be synthesized in four steps from l,2-bis(5-bromo-2-methyl-3-thienyl)perfluorocyclopentene by the Sonogashira coupling reaction (05T12256). 

A comparative analysis of the spectroscopic and photochromic properties of dithienylperhydro- and perfluorocyclopentenes were reported in 03EJO1887 and 05JPC9437. Their photochromic properties are similar, but the perhydro derivatives were shown to be thermally and photochemi-cally less stable. 

Unsaturated perfluoro- or polyfluorohalocycloalkenes are hydrolyzed in alkaline media. Perfluorocyclopentene, when treated with alkali, gives 2//-pentafluorocyclopenta-l,3-dione (14).21... 

Perfluorocyclopentene when treated with potassium hydroxide in methanol gives heptafluoro-2-methoxycyclopentene (19) in 62% yield and with sodium methoxide yields product 19, hexa-fluoro-l,2-dimethoxycyclopentene (20), and pentafluoro-3-methoxycyclopent-2-enone (21).72... 

Figure 1 shows a typical diarylethene derivative absorption spectral change.1121 Upon irradiation with 313 nm light, a colorless hexane solution of l,2-bis(2,4-dimethyl-5-phenylthiophen-3-yl)perfluorocyclopentene la turned blue, in which an absorption maximum was observed at 562 nm. 

---