Spiropyran compound

A spiropyran compound bearing a pyridinium group and a long alkyl chain behaves as a surfactant. The components shown in Scheme 1 exhibit reverse photochromism in polar solvents. The colored merocyanine form is more stable than the spiropyran form in the dark. Upon photoirradiation at A>510 nm, the polar merocyanine form is converted to the hydrophobic spiropyran form so that the CMC (critical micelle concentration) of the surfactant decreases. Consequently, when the initial concentration is set between the CMC of the two forms, photoirradiation induces a sudden formation of micelles at a certain conversion to the spiropyran form corresponding to the CMC of the mixed micelle of the two forms. 

Photoresponsive polymers can be obtained by introducing photochromic units, such as azobenzene or spiropyran groups, into the macromolecules of polymeric compounds. As described in Chapter 1 of this book, photochromic compounds can exist in two different states, such as two isomeric structures that can be inter-converted by means of a light stimulus, and the relative concentrations of which depend on the wavelength of the incident light. For instance, in azobenzene compounds, photochromism is due to trans-cis photoisomerization around the N=N double bond, while in spiropyran compounds photochromism involves interconversion between the neutral spiro form and the zwitterionic merocyanine form (Figure 1). 

Fig-1 Photochemical reactions responsible for photochromic behaviour in a) azobenzene derivatives, b) spiropyran compounds, c) fulgides, and d) triphenylmethane derivatives. 

T. Yoshida, A. Morinaka, and N. Funakoshi, UV Light assisted vacuum deposition of spiropyran compounds, Thin Solid Films, 162, 343-352(1988). 

V. Pimienta, G. Levy, D. Lavabre, A. Samat, R. Guglielmetti, and J. C. Micheau, Computer analysis of the thermoreversible photochromism of spiropyran compounds evaluation of absorption spectrum and quantum yield, Mol. Cryst. Liq. Cryst., 246, 283-286 (1994). 

T. Tanaka, T. Imura, K. Tanaka, and Y. Kita, Spiropyran compound Mid its manufacturing method, Japanese Kokai Pat. 02,69,471 (1990). 

M. Melzig and H. Zinner, Photochromic spiropyran compounds, World Pat. Appl. WO 95/00504 (1995). 

However, the spiropyrane compounds are not useful to determine the polarity of ionic liquids with strong hydrogen-bond acceptors as complexes form that exhibit no solvato/photochromism. 

The novel synthesis of spiropyranes and w-spiropyrane compounds were described in a recent report, which employs ultrasound as the energy source to promote the condensation reaction between the indoline or the w-indoline and the desired salicylaldehyde, as well as the potential of the method which offers advantages over the conventional method. The photochromic compounds employed in this study are shown in Figure 1. 

Moreover, a low molar mass spiropyran compound entrapped in a membrane consisting of plasticized poly(vinyl chloride) rendered the latter photoresponsive. A membrane potential change of more than 100 mV was induced by irradiation with light [27]. For further details and additional references, the reader is referred to the relevant reviews [11, 28]. 

The reaction between isatin derivatives 44, malonodini-trile 21, and CH acids 43 led to the formation of spiropyran compounds 46 by the application of a variety of catalysts. Yuan et al. reported the use of 10mol% cupreine 45 as an organocatalyst that led to spiro compounds with enhanced enantiomeric excess (Scheme 13.15) [23]. The reactions are conducted in dichloromethane or 1,2-dichloroethane as solvents at 0 °C, while the addition of 4 A molecular sieves provides shorter reaction times and higher ee s. 

When spiropyrans are treated with acids they are converted into spiropyran salts , which exhibit photochromic behavior differing from that of the parent spiropyran compounds. The gross mechanism proposed is illustrated in Figure 14.9. In the dark at room temperature, the compounds give colored solutions due to the presence of the 0-protonated merocyanine species III. The open form is converted by irradiation with visible light to the iV-protonated spiro form IV. As spiropyrans are fairly strong bases in the open form but very weak bases in the clos spiro form, the charged species IV can lose a proton and the neutral species I can be actually formed. 

Plaquet, A, Guillaume, M., Champagne, B., Castet, F., Ducasse, L., Pozzo, J.L., and Rodriguez, V. (2008) In silico optimization of merocyanine-spiropyran compounds as second-order nonlinear optical molecular switches. Rhys. Chem. Chem. Phys., 10, 6223-6232. 

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