Metals photochromic crown ethers

It is known from literature that several reversible photochemical reactions, such as geometric isomerism of azobenzene [7], electrocyclic reaction of dihydroindolizines, fulgides and diarylethylenes with heterocyclic groups [8-10], dimerization of anthracene [11], and photochromic reaction of spirocompounds [12] have been also employed to provide photocontrol over metal-ion binding ability of crown ethers. 

It was found that the linking of styryl dye fragment to benzocrown ether results in novel photochromic compounds CESD (Crown Ether Styryl Dyes) possessing interesting physico-chemical properties (Scheme 1) [13], The dyes are intensively colored and show significant hypsochromic shifts upon complexation with alkaline earth metal cations in acetonitrile solution. Reversible photochemical reaction E,Z-isomerization is observed for both dyes and their complexes. 

Takeshita, M., Irie, M. (1998) Photoresponsive tweezers for alkali metal ions. Photochromic diarylethanes having two crown ether moieties, J. Org. Chem., 63, 6643-6649. 

The photochromism of fulgide-related diesters (fulgenates) 7-9, possessing crown-ether moieties, is described in Section 4.2. The most notable feature was that photochromic coloration did not occur when a host-specific alkali metal salt was added.181... 

The ability to tune the photochromic behavior of crown ether-bound spiropyrans, 4a and 5a, by connecting them to metal ions, was investigated by Kimura and his coworkers [10,11]. This complexation of the crown ether moiety with a metal ion accelerates the transformation from spiropy-ran, 4b to merocyanine, 4c, by light or heat. When this complexation effect is weak, thermodynamic equilibrium favors the spiropyran form, and... 

Spironaphthoxazine with a crown ether, 8, also shows photochromic behavior that is sensitive to the type of alkali and alkaline earth metal ions [14]. Other derivatives of spiropyran and spiro oxazine, 9-12, which can chelate metal ions were synthesized, and the effects of complexation on their photochromic behavior have been investigated [15-17]. 

The photochromism of spirobenzopyrans is a well-documented phenomenon that arises from the photoinduced reversible isomerization between spiropyran and merocyanine forms . In spirobenzopyrans carrying a crown ether moiety (e.g., Ill), this interconversion process is affected by metal ion complexation. A strong interaction of the crown ether unit with a metal ion caused the thermal isomerization of the spirobenzopyran residue to the corresponding merocyanine form with simultaneous suppression of the UV-induced isomerization process (negative photochromism) (Scheme 3). Conversely, a weak metal ion interaction induced a positive photochromism <2001JOC1533, 2002EJ0655>. 

Kimura et al. [259] reported applying organic photochromic compoimds to photochemical switching of metal-ion complexation and ionic conduction by combining photochromism with metal-ion binding property of crown ether derivatives. They synthesized vinyl polymers, incorporating a crowned spirobenzopyran moiety at the side chain ... 

Crown ether-bound styryl dyes have been studied by Fedorova and her coworkers. The photochromic properties of the dyes, 91, are based on reversible trans-cis isomerization and [2 + 2]-photocycloaddition. They exhibit a strong preference for formation of complexes with heavy metal ions [72]. Due to its specific structure, the betaine-type dye is able to form an anion-capped trans-isomer. Intramolecular coordination in the anion-capped isomer enhances its stability and causes a sharp deceleration of its dark trans-... 

The photoinduced expulsion of metal ions can also be achieved by the coupling of the crown-ether moiety into the family of the photochromic triarylmethane leuconitriles... 

Alfimov, M.V., Vedernikov, A.I., Gromov, S.P., Fedorov, Yu.V., Fedorova, O.A., Churakov, AV., Kuz mina, L.G., Howard, J.A.K., Bossmann, S., Braun, A, Woemer, M., Sears, D.F., Saltiel, J. (1999) Synthesis, structure and ion selective complexation of trans and cis isomers of photochromic dithia-18-crown-6 ethers, J. Am. Chem. Soc., 121, 4992-5000 b) Stanislavskii, O.B., Ushakov, E.N., Gromov, S.P., Fedorova, O.A, Alfimov, M.V. (1996) Crown-containing styryl dyes. 14. The influence of N-substitute length on the complex formation of betainic chromogenic 15-crown-5-ether with alkaline earth metal cations, Russ. Chem. Bull, 45, 564-572. 

---