Photochromism of 2-Oxaindan Spiropyrans

SP14-SP17 in liquid and solid solutions are characterized by photochromic 

An increased interest in the synthesis and study of new photochromic spiro-oxazines (SOs) is due to their improved properties compared to SPs, i.e,. then-stability to photodegradation.64 This has stimulated research on the influence of specific structural features of SOs on their properties. The SOs that have been studied by X-ray diffraction analysis to date can be divided into two groups derivatives ofbenzoxazines and derivatives of annellated benzoxazines. The latter 

When the indoline ring is nonplanar, the N(2) has a pyramidal configuration and lies out of the plane of the adjacent atoms by 0.10-0.30 A. The sum of the bond angles at the nitrogen atom N(2) is 340-356.1°. 

The structure of SOI 1 was not affected by annellation of another potentially photochromic chromene ring at the 9- and 10-positions of the naphthalene moiety. Within the limits of experimental error, the Cspiro—0(1) [1.448(8) A] and Cspiro-N(2) [1.424(8) A] bond lengths coincide with the lengths of the analogous bonds in SO 10 and S04. 

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. 

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