Bis photochromes

M. Holderbaum, H. Durr, and E. Hadjoudis, Novel bi-photochromic systems dihydroindolizines with Schiff base moiety, JPhotochem. Photobiol. A, 58, 37-50 (1991). 

Smets and coworkers worked with stretched spirobenzopyran rubber networks obtained by copolymerization of ethyl aaylate with variaWe amounts of a bis-photochrome dimethacrylate as cross-linking agent, namely l,l -(a,a -p-xylyl)-bis-[3, 3 -dimethyl-8-methacryloyloxymethyl-6-nitro-spiro(2H-l-benzopyran-2,2 -indoline)]. The chemical structure of these DIPS-rubbers is given in Fig. 11. 

Fig. 11. Photochromic polyfethyl acrylate) rubber cross-linked with bis-photochrome dimethacrylate...

Holderbaum, M., Dtirr, H., and Hadjoudis, E., Novel bi-photochromic systems dihydroindohzines with a Schiff base moiety, /. Photochem. Photobiol, A Chem., 58, 37, 1991. 

The benzospiropyran polymer networks having spirochromophores as cross-linking agents were made by copolymerization of ethylacrylate with variable amounts of bis-photochrome dimethacrylate, l,l-(a,ot -/7-xylyl)-... 

The copolymerizations were carried out in benzene solution (50 vol%), in the presence of diisopropyl peroxydicarbonate as the initiator, on the surface of glass or mercury. A representative condition is 100 mmol of ethylacrylate, 0.66 mmol of bis-photochrome dimethacrylate, and 0.096 mmol of diisopropyl peroxydicarbonate. Table 4 summarizes the photoresponsive polymers with spirobenzopyran chromophores. 

The classical example of a photochromic process involving an homolytic dissociation is the formation of a red-purple free radical by photolysis of bis(2,4,5-triphenyliniida2ole) [63245-02-3] C 2B3qN (2 )-... 

The use of an electron-accepting counter ion leads to a photochromic system that is highly reversible under an inert atmosphere. An anion that has been used successfully is tetra-bis[3,5-di(trifluoromethyl)phenyl]borate anion [79250-20-9], C22H22BF 24 ( )-... 

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 a series of studies, substituents were introduced or varied at the 2-positions of the thiophene rings of di(benzothienyl)ethenes. The reactions of 3-bromo-2(n-aIkyl)-l-benzothiophene with BuLi and octafluorocyclo-pentene gave bis(2-n-alkyl-l -benzothiophen-3-yl)perfluorocyclo-pentenes 60 containing alkyl substituents with a different chain length at position 2 of the benzothiophene ring. The authors stated that the Et-, Pr-, and Bu-containing derivatives exhibit photochromic properties even in the crystalline state (06JPP(A)162). 

The synthesis of photochromic 6n conjugate systems having a bis(2,3 -benzothienyl) unit 75 was described (04CC1010) (Scheme 23). These systems have unusual structures, in which the fluorine atom, the methyl group, or the trifluoromethyl group rather than the heterocycle is located in a vicinal position adjacent to the benzothienyl substituent in the per-fluorocyclopentene moiety. 

The reaction of 2,5-disubstituted 3-furyl bromides with butyl-lithium and octafluorocyclopentene in dry tetrahydrofuran (THF) at —78°C gave bis(furyl)ethenes 82 (06JMC4690). Photochrome 83 (05JOC10323, 06EJ03105) (29-46% yield) and a series of its derivatives 84 (55-65%) containing different substituents at position 6 of the ben-zofuran ring were synthesized from 3-bromo-2-methyl-1-benzofuran (08JPP(A)146). 

Thenoines with urea in acetic acid give 4,5-bis(2,5-dimethyl-3-thienyl)-lH,3H-imidazol-2-one 239, whose treatment with acid chlorides affords photochromes 240 in good yields (02IZV1588). Thenoine 213 with an excess of l,l -carbonyldiimidazole produces l,3-dioxol-2-ones 241 in high yields (02IZV1588). However, thenoine with l,l -thiocarbonyldiimidazole gives 4,5-bis (2,5-dimethyl-3-thienyl)-l,3-oxathiol-2-one 242 instead of the expected thione (04ZOR1743) (Scheme 69). 

The synthesis of a fluorescent photochromic system 274a with a high fluorescence contrast ratio by covalently joining a highly fluorescent zinc bis(acylamidine) allowing effective energy transfer from the excited state of the dye to the photochromic component has been reported (08JPP(A) (200)74). 

Fused aziridines are interesting compounds owing to the fact that the strained three-membered ring can easily open and cause dipolar cycloaddition reactions as well as their photochromic properties. Therefore, most of this chapter covers the chemical and photochemical properties of bi- and tricyclic aziridines. Some properties of aziridinyl ketones are also reviewed, in particular, reactions leading to aziridinyl anils. 

The fullest investigation of the photochromic properties of various bi- and tricyclic aziridines in the crystalline state and systematization of the data were carried out by Orlov et al. [120] with aziridines containing different substituents R, Ri and the bridge group M (Scheme 1.45). 

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