Spirooxazines , photochromic

S. Aramaki and G. H. Atkinson, Spirooxazine photochromism picosecond time-resolved Raman and absorption spectroscopy, Chem. Phys. Lett., 170, 181-186 (1990). 

N. Tamai and H. Masuhara, Femtosecond transient absorption spectroscopy of a spirooxazine photochromic reaction, Chem. Phys. Lett. 191, 189-194 (1992). 

G. Baillet, G. Giusti, and R. Guglielmetti, Study of the fatigue process and the yellowing of polymeric films containing spirooxazine photochromic compounds, Bull. Chem. Soc. Jpti. 68, 1220-1225 (1995). 

SURVEY OF VIBRATIONAL STUDIES ON SPIROPYRAN AND SPIROOXAZINE PHOTOCHROMES... 

J. Aubard, P. Lareginie, G. Buntinx, V. Lokshin, G.Levi, and R. Guglielmetti, Time-resolved resonance Raman spectroscopy of spirooxazine photochromes Experimental evidences for a TTC isomer open form in various solvents, J. Raman Spectrosc. (to be submitted). 

Spirooxazine is an aza analogue of spiropyran in which the carbon atom at 3-position is replaced by a nitrogen atom. Historically, the photo-chromic phenomenon of spiroindolinooxazine derivatives was found after discovery of photochromic spiroindolinobenzopyran.72... 

Spirooxazine compounds are useful in the field of plastic lenses, such as sunglasses and ski goggles. The plastic photochromic sunglasses have been in the marketplace since the early 1980s, and their market share is presently ca. 70%. The excellent lightfastness of the spironaphthooxazine series makes such applications possible, compared to other photochromic compounds. 

Scheme 10.4 Reversible photochromism of spirooxazine 247 involving interconversion with...

Photochromic systems that have been examined in both of these approaches include spiropyrans, spirooxazines, diarylethenes, dihydroindolizines and azoben-zenes. A schematic of a disk structure is shown in Figure 1.14. To produce the... 

Spiropyrans, and spirooxazines, better known for their photochromic behaviour (see sections 1.22 and 1.23), also exhibit thermochromism. The ring opening to produce the highly coloured merocyanine form is induced by heating either the solid or... 

There have been relatively little ultraviolet-visible (UV-Vis) spectroscopic data for 1,4-oxazines, but selected data are presented in Table 8. UV spectroscopy is important for photochromic compounds, such as spirooxazines. The UV spectra of 33 spirooxazines in five different solvents are collected in a review <2002RCR893>, and the more recently reported examples of photochromic oxazines 65, 66, 101, and 102 are shown here. It can be seen from Table 8 that both adding methoxy substituents to the oxazine and changing to a more polar solvent give a UV maximum at a higher wavelength. This solvent effect can also be seen in the case of 102, which also has important fluorescence properties, discussed in Section 8.06.12.2. 

The merocyanine form of spirooxazines can react with free radicals, which is important as it causes degradation of the photochromic materials <1995JOC5446>. 

Cycloadditions have also been used to form benzoxazines, especially in the syntheses of photochromic materials. The reactants are typically an alkene such as 296 and a phenanthrenequinone monoxime or a l-nitroso-2-naphthol 295. Scheme 32 shows the synthesis of two photochromic materials 297 and 116 <1981TL3945>. The latter is a spirooxazine, for which a two-step mechanism, also shown in Scheme 32, was later suggested <2004BMC1037>. 

The medicinal use of the photochromic oxazine 379 was discussed in the previous section. The principle of photochromism was shown in Scheme 3, Section 8.06.5.1. Photochromic spirooxazines 101, 116, and 297 that have appeared in this chapter and their various substituted derivatives have been patented as photochromic materials <2003WO42195> and used as photochromic dyes in a microsphere-based sensor <2005USP19954>. The compound 299 is also used as photochromic material <2005S1876>. More detailed information about the applications of spirooxazines can be found in a review <2002RCR893>. The phenoxazine 380 has also been patented for use in optics <2005SUA2246491>. 

Their resistance to photooxidation is also good relative to most other families of photochromic compounds. In this property they are comparable to the spirooxazines, which again adds to the complementary character of the two families. The color of the open forms can be tuned over a large range of the visible spectrum, by substituents on the naphthyl moiety or on the aromatic groups present on the sp3 carbon atom of the pyran ring. 

J. Aubard, C. M Bossa, J. P. Bertigny, R. Dubest, G. Levi, E. Boschet, and R. Guglielmetti, Surface enhanced Raman spectroscopy of photochromic spirooxazines and related spiropyrans, Mol. Cryst. Liq. Cryst., 246, 275-278 (1994). 

The first photochromic spirooxazine compounds synthesized (1970) belonged to the spiroindolinonaphthoxazine ring system. Generally, they were colorless in dilute organic solvents and polymer matrices and became blue upon exposure to UV light. 

The photochromic response of spirooxazines was shown to be somewhat affected by the substituent on the indolino nitrogen5 (Table 2.2). For various 1-alkyl-5,6-dimethyl-9 -methoxy NISOs in cellulose acetobutyrate, photochromic activity increased in the order 1-methyl < 1-ethyl < 1- n-propyl < l- -butyl. However, the effect was not straightforward. 

The spirooxazines derived from hydroxynitrosodibenzofurans have been disclosed by Yamamoto and Taniguchi.13 These photochromic compounds are interesting because their colored forms have two absorption bands in the visible range. For instance, compound 17 had absorption bands at 460 and 632 nm in methyl alcohol after UV irradiation. 

Aramaki et al.30 examined the photochromic reactions of spirooxazines by picosecond time-resolved Raman spectroscopy. Vibrational resonance Raman spectra of the merocyanine isomer(s) recorded over a 50-ps-1.5-ns interval did not change. This indicated that the open ring opening to form a stable merocyanine isomer or the distribution of isomers31 was complete within 50 ps and that the isomer(s) distribution remained unchanged for at least 1.5 ns. 

Malatesta35 proposed the key intermediate product (compound 28) of the oxidative degradation of photochromic spirooxazines. These species may result from the photochromic irreversible degradation of the spirooxazines even under conditions of partial or total absence of oxidation as, for example, in polymers coated with thin films of barrier agents such as SiO 2, SiOxCy, AI2O3, and MgO. 

Malatesta et al.36 disclosed that spirooxazines react easily in their open merocyanine (MC) forms with free radicals to give deeply colored, reduced, free-radical adducts (FRA) that are devoid of photochromic activity. The radicals attack the C5I=C6 double bond of MC and yield stable, deeply colored, free-radical adducts (compound 29) that can no longer close back to the corresponding spiro form. The adducts absorb in the 510-560-nm region and are characterized by high molar absorptivities. 

Kawasaki et al.40 disclosed the use of hindered phenols such as 2,6-di(tert-butyl)phenol as stabilizers for spirooxazines in poly (vinyl butyral). The hindered phenols not only improved photochromic durability but also photochromic response, besides accelerating the thermal recovery rate. 

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