The results of studies on the structure and nature of the electronic states of spiropyrans (SP) and the products of their photochromic reactions as well as the mechanism of the dissociation of the Cspiro–O bond and the formation of a coloured form of the SP are surveyed and analysed. Also analysed are the mechanisms of the α-dissociation and predissociation of the bond, which make it possible to explain satisfactorily the dependence of the quantum yield of the photocolouring reaction on the structure of the SP, the nature of the matrix, and temperature. The prospects for the utilisation of the photochromic SP are discussed. The bibliography includes 179 references.

https://iopscience.iop.org/article/10.1070/RC1987v056n02ABEH003262/pdf

The Photochemistry and Photophysics of Spiropyrans

The synthesis and spectrokinetic properties of photochromic spiropyrans in solution are reported. The most important results obtained during the last two decades, including the synthetic access to azaheterocyclic and non-azaheterocyclic spiropyrans are described, as each series confers its own particularities to the photocoloration. The influence of the structure (skeleton, heteroatoms, substituents) on the stability of the photomerocyanines is discussed in terms of electronic (correlation of Hammett type) and steric effects. The role of structural parameters and of solvent effects on the electronic distribution of the colored form is also emphasized.

Synthesis and Spectrokinetic Properties of Photochromic Spiropyrans

This chapter describes the formation of bicondensed products resulting from the reaction in a basic medium of a 2,3-dimethylbenzothiazolium salt and salicylaldehyde, under specific conditions. It also explains the mechanism of their formation, decomposition, and the influence of the nature of the quaternary salt or the aldehyde substitution on the condensation behavior. Based on this understanding, it can be concluded that two competitive reactions with the intermediate anhydrobase occur. A mechanism to explain the formation of bicondensed products is proposed, with evidence for their dissociation in solution (in acid or neutral medium). The use of spectroscopic evidence (nuclear magnetic resonance (NMR)and electron spectroscopy) for the degradation of the bicondensed products is also presented. Finally, the chapter describes a thermographic recording material based on the thermoreactive properties of the bicondensed products.

Chapter 23 – Spiropyrans and Related Compounds

Spectrophotometric and ESR measurements have been made in a study of photodecomposition and thermodecomposition reactions of spiropyrans (SPs) of the indoline and oxaindan series of solutions and in the crystalline state, at various temperatures. From an analysis of the experimental data, involving certain concepts developed previously regarding the mechanisms of photochemical reactions of SPs, it has been concluded that the most probable reactions of photodecomposition and thermodecomposition of SPs are α-rupture of a bond and the formation of a chemically active biradical, as well as irreversible reactions of SP ion radicals that arise as a consequence of phototransfer and dark transfer of electrons in associates of various species of the SP.

Mechanism of photodecomposition of spiropyrans

Synthesis of a new photo-stable spiropyran

3′, 3′-Dimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline) -1′-propionic acid [I] was modified with a methoxy group at 8th position of the pyran ring. The stability of photoresponsive activity was 3.4 times higher than that of [I]. The new spiropyran is promising for the photocontrol of enzyme activity.

KarubeIsao

Papers

Synthesis of a new photo-stable spiropyran.