Spiro indoline-2,4 pyrans

C. Salemi, G. Giusti, and R. Guglielmetti, DABCO effect on the photodegradation of photochromic compounds in spiro[indoline-pyran] and spiro[indoline-oxazine] series, J. Photochem. Photobiol. A Chem., 86, 247-252 (1995). 

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. 

I. I. Chuev, O. S. Filipenko, S. M. Aldoshin, and O. A. Kozina, Molecular structure of l, 3, 3-trimethyl-6-[(trifluoromethyl)sulfonyl]spiro[indoline-22,2 -benzo[i>]pyran], Russ. Chem. Bull. 43, 1857-1859 (1994). 

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... 

Fig. 5 Smart UV-responsive coating on silica nanoparticles with PNIPAM brushes functionalized with FRET donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,l,3-benzoxadiazole (NBDAE), and photoswitchable acceptors, l -(2-methacryloxyethyl)-3, 3 -dimethyl-6-nitro-spiro(2//-l-benzo-pyran-2,2 -indoline) (SPMA). The UV radiation induces the change from colorless spiropyran derivatives in the outer part of the coating (7) to the fluorescent merocyanine form (2). Thus, FRET with the benzoxadiazole moieties in the inner part of the coating is enabled and the fluorescence color changes from green to red. By variation of the temperature and induction of a collapse of the PNIPAM chains (3), the FRET efficiency can be tuned (4). Reprinted, with permission, from [70], Copyright (2009) American Chemical Society...

Unlike the still-unknown 277-pyran which exists exclusively in the ring-opened form, 277-thiopyran is a well-characterized molecule. Nevertheless, the S-C(2) bond can be cleaved and this is the basis of the photochromic properties observed with spirobenzothiopyrans. Irradiation at 365 nm of the spiro[2/7-l-benzothiopyran-2,2 -indoline] 273 in both the solid state and in solution results in opening of the thiopyran ring and the formation of a colored metastable zwitterionic merocyanine (Equation 21). The open form exhibits solvatochromism, with Amax 588 nm in methanol and 673 nm in acetone. In solution, the thiopyran unit reforms rapidly when irradiation ceases, but continuous irradiation leads to the growth of crystals of the open form <2002JOC533>. 

Spiropyrans SP-2, reported by Miyashita et al., forming chromium complexes on their indoline phenyl ring, can possibly take two diastereomeric spiro forms >[47]. Because of the favorable interaction of the pyran oxygen atom and the chromium atom, the thermal ring closure occurred diastereomerically to give only one diastereomer from the planar merocyanine form generated by photoirradia-... 

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