Spiropyrans thermochromic properties

V S. Marevtsev, L. L. Zaichenko, V D. Ermakova, S. I. Beshenko, V. A. Linskii, A. T. Gradyushko, and M. I. Cherkashin, Effect of electron-donating and electron-accepting substituents on photo- and thermochromic properties of indolino-spiropyrans, Bull. Acad. Sci. USSR, Chem. Sci. 29, 1591— 1596 (1980) Chem, Abstr. 94, 29901 (1980). 

S. M. Aldoshin, V. A. Lokshin, A. N. Rezonov, N. V. Volbushko, N. Shelepin, M. I. Knyazhanskii, L. O. Atovmyan, and V. I. Minkin, Structures and photo- and thermochromic properties of spiropyrans of the 2-oxaindan series with polycondensed chromene fragments, Chem, Heterocycl. Compd. 1987, 614-624 Chem. Abstr. 108, 131516 (1987). 

As distinct from photochromic spiropyrans and spirooxazines, [2//J-chro-menes do not contain a heterocyclic fragment such as an indoline nucleus. Consequently, in such compounds there are no specific n-a orbital interactions that elongate and weaken the C, iro—O bond, the ruptures of this bond in the excited and ground states being responsible for the photo- or thermochromic properties of spiropyrans and spirooxazines as well as [2// -chromcncs. 

The thermochromism of spiropyrans, discovered in 1926, has been extensively studied. Nearly every known compound of this class leads to deep color on melting (generally red, purple, or blue). However, heating solutions of spiropyrans also causes coloration. Day1 in his review gave a table reporting essentially thermochromic spiropyrans of the indoline and spirobipyran series. Bertelson6 summarized the main spectroscopic and physicochemical data obtained up to 1971. Thermochromic properties of spirooxazines have been more recently reported.7... 

During the past decade, new thermochromic spiropyrans have been described, particularly by Russian teams. For example, spiropyrans of the 2-oxaindane or azaindanone series with polycondensed chromene fragments (1-8), exhibiting photo- and thermochromic properties, have been synthesized by Minkin and co-workers.19,20... 

Krasieva and co-workers21 mentioned the thermochromic behavior of spiropyrans of the dithiolane series (9, 10). These data confirm that the annellation of the benzopyran moiety favors the thermochromic properties of this class of compounds. 

Although the thermochromic properties ofmonospiropyrans (with one pyran ring) have been described extensively, bis-spiropyrans with various structures have also been studied. For bis-spiropyrans in which the merocyanine fragments are... 

V.A. Linskii, T. Gradyushuko and M.I. Cherkashin, Effect of electron donor and electron acceptor substituents on photo and thermochromic properties of indoline spiropyranes. Isv. Akad. Nauk. SSR, Ser. 

B. B. Safoklov, B. Lukyanov, A. O. Bulanov, et ah, Photo- and thermochromic spiropyrans. 21. 2,8"-Formyl-3,6"-dimethyl-4-oxospiro(3,4-dihydro-2H-l,3-benzoxazine-2,2"-[2H]chromene) possessing photochromic properties in the solid phase, Russian Chemical Bulletin, vol. 51, no. 3, pp. 462-466, 2002. 

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