Spiropyran metal ions

A spiropyran with a methoxy group at the eight-position, 2a and its derivatives show a blue shift of the absorption peak when a metal ion is attached to form a chelate complex, 2b [4,5]. The type of metal ion has little effect on the wavelength of the absorption maximum, kmax, but it has a strong influence... 

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]. 

L. Atabekyan and A. Chibisov, Spiropyran complexes with metal ions. Kinetics of complexation, photophysical properties and photochemical behavior, Mol. Cryst. Liq. Cryst., 246, 262-266 (1994). 

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>. 

There continues to be a high level of interest shown in photochromic systems. The optically active l,T-bi-2-naphthol gives an optically active intramolecular addition product (37) on irradiation, and on prolonged exposure, cycloreversion occurs which gives evidence for a photoequilibrium between the asymmetric molecules (Cavazza et al). A number of reports within the year describe a variety of aspects of the well-known thermally-reversible spiroindoline-oxazine to photo-merocyanine conversion. For example, the process is sensitised by triplet cam-phorquinone (Favaro et al.), the influence of complexation on indoline and phenanthroline spiropyrans with transition and rare earth metal ions has been described (Atabekyan et al.), and the photochromism of other derivatives in water using vesicles and y-cyclodextrin is reported to be faster than in methanol with the process most favoured in the vesicles (Ishiwatari et al.). 

The Zv - complex of the merocyanine system (57) releases the zinc when it is irradiated with visible light and this results in the formation of the colourless closed spiropyranindoline (58, R = H). When the irradiation is stopped the Zn " complex reforms but this does not happen with the nitro derivative (58, R = NO2) in which it is thought that the nitro group stabilises the phenoxide ion in the open form. Other workers have also studied the complexation of spiropyran based merocyanines with transition and rare earth metal ions. An investigation of the influence of Lewis acids (hexa-fluoropropanol, trifluoroethanol and 2-fluoroethanol) on the stability of the coloured form of spiropyran and spirooxazines has been reported. Protonation of the open system produces a form that is photochemically inert and the behaviour of these acids is markedly different from that of acetic acid with such systems. 

Iron-arene complexes are known to exhibit extremely high photoactivity as initiators. Quantum efficiencies have been found to be greater than I in the photopolymerisation of dicyanate esters. Phenylglycine derivatives have been found to be excellent co-synergists for the iron-arene complexes when used in conjunction with dyes and amines. Complexes of various types have also been proposed. Maleic anhydride-THF complexes have been used for the photopolymerisation of oligourethane acrylates while metal-ion complexes of spiropyran copolymers undergo reversible polymer precipitation. Azo and polyazo initiators have been used to make butadiene-isoprene block copolymers while charge-transfer complexes of morpholine-chlorine induce the radical polymerisation of methyl methacrylate. The presence of zinc chloride enhances the... 

Another application of a photochromic reaction involves the reversibile size control of gold aggregates in nanoparticles by using 5-functionalized spiropyran derivatives. In the dark, the merocyanine form associates with each other, which suppresses the thermal rearrangement. Irradiation, on the contraiy, accurately tunes the dimension of the aggregates due to the different electrostatic properties of spiropyran and merocyanine (Fig. 3). In photocatalysis the effect of changing parameters is often limited, because the process of photon absorption photoexcitation of adsorbate -metal bond occur at some distance. It has recently been shown that when sub 5 nm metal particles are used, the hybridized absorbate-metal ions is excited preferentially. This results is an increased proportion of CO oxidation in H2 rich streams (Fig. 4). ... 

The crowned spiropyran in the electrically neutral form can bind an alkali metal ion with the crown ether moiety. At the same time, the spirobenzopyran portion isomerizes to the corresponding merocyanine form photo-chemically. The zwitterionic merocyanine form of crowned spirobenzopyran moiety brings about a significant change in the metal-ion binding ability. This prompted the authors to apply the compound to photo-responsive ion-conductive materials. They observed that the ion-conductivity was increased by ultraviolet light and decreased by visible light [259]. 

New fluorescent chemosensors for metal ions in solution 12CCR170. Organic nanoparticulate photochromes (mainly, spiropyrans, spirooxa-zines, and diarylethenes) 13COC1771. 

Figure 49 Photocontrol of metal ion binding by aza-crown ether-containing spiropyrans. (Reproduced from Ref. 92. Royal Society of Chemistry, 1991.)...

Extension of this work to other aza-crown ethers and thiacrown ethers containing spiropyrans, spirooxazines, and spirothiopyrans (Figure 50a), based on similar design principles for the binding of different types of metal ions, has subsequently been reported. " " On the other hand, Inouye and coworkers also reported cryptand-containing... 

Application studies of these crown ether-containing spiropyrans as metal ion transporters in liquid membranes (Figme 51a) have also been examined under various lighting conditions. The transportability of Li+ increases... 

Figure 52 Photoswitchable metal ion binding of an iminodiacetate-substitnted nitro-spiropyran. (Reprodnced from Ref. 101. American Chanical Society, 2008.)...

Wojtyk, J.T.C., Buncel, E., and Kazmaier, P.M. (1998) Effects of metal ion complexation on the spiropyran-merocyanine interconversion development of a thermally stable photo-switch. Chem. Commun., 1703-1704. 

K. A. Chibisov and H. Corner, Complexes of spiropyran-derived merocya-nines with metal ions relaxation kinetics, photochemistry and solvent effects, Chemical Physics, vol. 237, no. 3, pp. 425—442, 1998. 

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