Spiro indoline-benzopyrans

Distribution of spin density in the framework of trianion-radicals allows determining whether or not there is some conjugation between substituents at different sites. For example, reduction of dinitro spiro(indoline-benzopyran) with potassium tert-butoxide in DMSO proceeds according to Scheme 1.40 (Alberti et al. 1995). 

As shown by means of electrochemical ESR spectroscopic methods and confirmed by ab initio calculations (Alberti et al. 1995), the first electron is accommodated in the more accessible nitrobenzopyran moiety. Next, the second electron fits into the nitroindoline moiety in virtually the same orbital that in the anion radical of mon<9-nitro-spiro(indoline-benzopyran), is occupied by the unpaired electron. The mono-nitro anion radical is also formed by the aforementioned reaction with terf-BuOK in DMSO, Scheme 1-63. 

As to the third step of the step-wise one-electron reduction of t//-nilro-spiro(indoline-benzopyran), the third extra electron is again accommodated into the nitrobenzopyran unit without affecting the spin density distribution on the opposite fragment, which therefore remains essentially identical to that of the anion radical of mono-nitro-spiro(indoline-ben-zopyran). Hence, the spiro-nodal carbon atom prevents conjugate interactions between the indoline and benzopyran moieties. 

This work has allowed an evaluation of the molar absorptivity of the colored species and the quantum yields of photocoloration and photodecoloration. The examples given include a dihydroindolizine compound, a spiro[benzothiazoline-benzopyran], a 2//-chromcne, a spiro[indoline-benzopyran], and the dimer of the triphenylimidazolyl radical. 

Spiro[indoline-benzopyran] 458 is a highly photodegradable photochromic molecule.59,60... 

In the study of photodegradation by conventional methods, the different reaction steps are very difficult or impossible to localize. For example, in the case of spiro [indoline-benzopyran] 4, one cannot be sure whether the stable closed form A or the open unstable form B is the photodegradable species. However, from the dynamic viewpoint, it can be shown that this problem can be resolved by discriminating two ideal kinetic schemes of the ABC type characterized, either by two parallel or two successive photochemical processes (ABC, 2cj)p, 1k, or ABC, 24>s Ik see Table 3). 

Activation energies for the ring opening and for the ring closure of spiro[indoline-benzopyrans] 67-76, spiro[indoline-naphthopyrans] 77-79, and spiro[oxaindane-pyrans] 4, 80 and 81 have been studied in amorphous vitreous state.50... 

This chapter, far from being exhaustive, is aimed at outlining the properties of the radical ions and of the free radicals derived from photochromic compounds independently of whether or not these paramagnetic species are involved in the photochromic process itself. In particular, it will deal with the EPR of dihydro-and dialkyldipyridyl radical cations (viologens) and of the radical anions of a variety of nitro-substituted spirofmdoline-benzopyrans], spiro[indoline-naphtho-pyrans], and spiro[indoline-naphthoxazines] as well as their triphenylgermyloxy nitroxides and with the triplet spectra observed upon irradiation of 2,2,4,4-tetrachloro-1 -keto-1,4-dihydronaphthalene. 

Spirofindoline-benzopyrans], spiro[indoline-naphthopyrans], and spiro[indo-line-naphthoxazines] can rather readily undergo electron-transfer processes in either direction i.e they can be readily oxidized and reduced. Because the presence of nitro groups in their molecular framework normally enhances the photochromaticity of these compounds, several combined electrochemical and EPR studies have been carried out on a variety of mono- and dinitro-substituted spiroindolinic photochromes.52 56-60... 

The numbering of spiropyrans adopted throughout this review is indicated in Figure 1.2. The nomenclature of the spiropyran 1 is given as 1, 3, 3 -trimethyl-spiro[2H-l-benzopyran-2,2 -indoline] it is referred to as spiroindolinobenzopyran and abbreviated as BIPS. 

The first method is perhaps the most common, and is exemplified by the condensation shown in Scheme 3 of a 2-alkyl heterocyclic quaternary salt or the corresponding methylene base with a 2-hydroxy unsaturated aldehyde grouping (which usually is part of an aromatic ring, as in salicylaldehyde). These intermediates have given a broad assortment of spiropyran classes. The ready availability of 1.2.3.3.-tetraalkyl-3/f-indoleninium salts and salicylaldehydes has led to a large number of spiro-(2i/-l-benzopyran-2,2 -indolines) [this name will be used in preference to the correct T,3 -dihydrospiro(2//-l-bcnzopyran-2,2 -(2 //(-indole)]. A common acronym for this class, BIPS, will be used in this chapter as both singular and plural. 

S.-R Heum, M.-S. Hur, P. M. Kazmaier, and E. Buncel, Thermo- and photochromic dyes Indolino-benzospiropyrans. Part 1. UV-VIS spectroscopic studies of 1, .3,.3-spiro(2 //-1 -benzopyran-2,2 -indolines) and the open-chain merocyanine forms solvatochromism and medium effects on spiro ring formation, Can. J. Chem., 69, 1940-1947 (1991). 

DIPS designates 3,3-dunethyl-spiro-2H-l-benzopyran-2,2 -indoline... 

Smets and coworkers worked with stretched spirobenzopyran rubber networks obtained by copolymerization of ethyl aaylate with variaWe amounts of a bis-photochrome dimethacrylate as cross-linking agent, namely l,l -(a,a -p-xylyl)-bis-[3, 3 -dimethyl-8-methacryloyloxymethyl-6-nitro-spiro(2H-l-benzopyran-2,2 -indoline)]. The chemical structure of these DIPS-rubbers is given in Fig. 11. 

Resonance Raman studies of the photochromism of 1 .3, 3trimethyl spiro - [2H-1 -benzopyran-2,2 -indoline] show at least four... 

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