Spiropyran fragments

Biphotochromic dyads containing dithienylperfluorocyclopentene and spiropyran (naphthopyran) fragments (05AG(E)5048, 05X3719) are... 

The main focus of this chapter is on two well-studied series of photochromic compounds, spiropyrans and spirooxazines, and the comparison of their photo-reactive excited states and molecular structures. The discussion of their photodegradation takes into account the results obtained from spectrophotometric measurements together with the identification of the fragments resulting from photodegradation. Different mechanisms are proposed for the photooxidation reaction. The experimental apparatus and procedures for photodegradation studies are also described. 

Although the proposed mechanism seems attractive and all the fragmentation products, except for the o-naphthoquinone 293, have been identified, it still remains to be demonstrated that the merocyanine forms of spiropyrans and spirooxazines have the ability to induce formation of singlet oxygen, a species on which the entire mechanistic scheme has been based. (This question is being addressed by Guglielmetti s group). 

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). 

Structure of Symmetrical Spiropyrans Consisting ofTwo Benzopyran Fragments... 

Oxaindan Spiropyrans with Polycondensed Chromene Fragments... 

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. 

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... 

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... 

Photochromic LC polymers are usually synthesized via the copolymerization of mesogenic monomers with photochromic mesogenic or nonmesogenic monomers similar to the synthesis of chiral LC polymers (Figure 19), hut, instead of a chiral monomer, a photochromic monomer is used as a mle, its concentration varies from 10 to 60mol.%. Diverse derivatives of azobenzene, spiropyran, diarylethenes, dnnamates, and coumarin-containing derivatives are used as photoactive fragments. 

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