Photochromic crown ethers

This review surveys our studies devoted to the photoswitchable molecular receptors based on photochromic crown ethers. Photochromic systems described in the review may be classified into three groups according to the reaction types E,Z-isomerization, [2+2]-photocycloaddition reactions and electrocyclic reaction. It has proved the groups to be an especially suitable basis for photochromic systems, and promising for the industrial applications. 

D.-X. Wu, P.-F. Xia, and H.-M. Zhao, Synthesis of photochromic crown ether merocyanine dyes and study of their reverse photochromism, Youji Huaxue, 12, 76-80 (1992). 

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. 

Fedorov, Yu., Fedorova, O., Schepel, N., Gromov, S., Alfimov, M., J. Saltiel (2004) Synthesis and multitopic complex formation of die photochromic bis-crown ether based on benzobis(thiazole), J. Phys. Org. Chem., in press. 

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]. 

H. Durr, A. Thome, H. Kilburg, S. Bossmann, E. Blasius, K. Janzen, and C. Kranz, Supramolecular effects on photochromism—Properties of crown ether-modified dihydroindolizines, J. Phys. Org. Chem. 5, 689-698 (1992). 

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>. 

Molecular design and applications of photochromic crown compounds 03BCJ225. New trends in the chemistry of condensed azacrown ethers and azathiacrown ethers 03JHC1. 

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 ... 

Functionalised conjugated polymers such as polythiophenes were studied from the point of view of the detection and transduction of chemical and physical information into an optical or electrical signal. Their ionochromism (reversible change of colour in the presence of ions), photochromism (reversible change of colour on exposure to light), affinity chromism (tendency to colour change) and electroluminescence of polythiophene complexes with crown ethers and other solutions are discussed in detail [295]. 

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-... 

---