Benzothiazolinic spiropyrans

R. Guglielmetti, R. Meyer, andC. Dupuy, Synthesis of a photochromic benzothiazolinic spiropyran,... 

The investigation of the colored form of spiropyrans by theoretical calculations started at the dawn of studies on photochromic compounds. The pioneering studies of a benzothiazolinic spiropyran were published by Guglielmetti and coworkers, who investigated the different planar forms of the open-form stereoisomers by calculations of the atomic interaction energies,31 the extended Hiickel method,3133 the PPP method,32 and theCNDO/2 method.34 The results of molecular mechanical (MM) calculations on spiropyrans and spirooxazines were compared with the X-ray structures and used to explain H NMR data.35... 

A. Samat, R. Guglielmetti, Y. Ferre, H. Pommier, and J. Metzger, Conformational study of the open forms of benzothiazoline spiropyrans by estimation of the steric interaction energy and the electronic stability of the system (EHT [extended Huckel theoryl Method),./. Chim. Phys. 69, 1202-1210 (1972). 

A. Le Beuze, A. Botrel, A. Samat, and R. Guglielmetti, Structural study of benzothiazolinic spiropyrans by the theoretical and experimental determination of dipole moments,/. Mol. Struct. 40, 77-87 (1977). 

H. Pommier, A. Samat, J. Metzger, and R. Guglielmetti, Electronic structure of benzothiazolinic spiropyrans (closed and open forms) by the CNDO/2 method, J. Chim. Phys. 72, 589— 594(1975). 

In view of the difficulties encountered in direct interpretation of the vibrational spectra of spiropyrans, Davin-Pretelli et al.w proposed a more rational approach. They investigated first the IR and Raman spectra of the two constituent moieties of the photochrome under study. Thus, from a preliminary IR and Raman study of benzothiazolines and 2/f-chromenes, which served as models, they were able to give a satisfactory assignment of the spectra of a series of benzothiazolinic spiropyrans.9 Moreover, on the basis of the vibrational data for 2//-chromenes, the set of bands at ca. 1250 cm-1 was unambiguously assigned to vibrations involving... 

M. Guiliano, E. Davin-Pretelli, G. Mille, J. Chouteau, and R. Guglielmetti, Infrared and Raman spectroscopic studies of benzothiazolinic spiropyrans and merocyanines, Helv. Chim, Acta 61, 1072-1085 (1978). 

Over the years, many spiropyran structures have been prepared. The pyran component consists of benzopyran or naphthopyran and the heterocyclic part consists of indoline, benzothiazoline, benzoxazoline, benzoselen-azoline, phenanthridine, acridine, quinoline, benzopyran, naphthopyran, xanthene, benzodithiole, benzoxathiole, and saturated heterocyclic rings such as pyrolidine and thiazolidine. 

Benzothiazolinospiropyrans 77 have been extensively studied by Gugliel-metti s group.31 Studies were carried out on aerated toluene solutions, and photodegradation was quantified in terms of V /2- The effect of substituents on both the benzothiazoline and chromene moieties was assessed. Photocolorability (Eapp) of this class of photochromes is, in general, lower than that of indolino-spiropyrans (Table 8). 

Guiliano et al. for benzothiazolinonitrospiropyrans9 (Spiro., Scheme 2). In the latter study, the photochromic conversion was performed by UV-irradiating the spiropyrans, dispersed in a solid matrix or dissolved in carbon disulfide (CS2), leading to thermodynamically stable colored species. The IR spectra ofthe colored states thus obtained were compared to those of a stable benzothiazoline photo-merocyanine in the solid state (R=OCH3) and a permanent merocyanine (R=H), (Mero., Scheme 2). From a detailed analysis ofthe IR spectra, it appeared that two... 

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