8-Methoxy-6-nitro BIPS

Equation (2.4.2.14), which considers only photodegradation, describes then only approximately the behavior of irradiated spiropyran solutions. The observed deviation is, in the author s opinion, derived from an oxidation process not included in Scheme 14 as the data reported in Figure 4 for 8-methoxy-6-nitro-BIPS (11) seem to indicate. 

Of the three compounds studied, 4, 8, and 11, 8-methoxy-6-nitro-BIPS (11) had the worst performance although it exhibited a very good colorability. The color-ability of spironaphthopyrans was low, and their fatigue resistance slightly better. Spirooxazine 8 has the best photostability and an acceptable colorability (Table 24). 

We have shown38 that 8-methoxy-6-nitro-BIPS (11) is the only photochrome able to sensitize the formation of (h with a quantum yield A = 0.15 that is about one-fourth that of a commonly used singlet-oxygen sensitizer, i.e. methylene blue, for which 0A = 0.57.39 This benzopyran behaves as a good quencher of l02 as well. Unfortunately, in the paper by Guglielmetti and co-workers an analysis of the... 

Detection by SERS of Degradation Products from UV-Irradiated Solutions of 8-Methoxy-6-Nitro-BIPS... 

The absorption maxima in toluene and ethanol, the thermal fade rate constants in toluene and dioxane, and the kinetic parameters AH and AS for a series of F-phenyl- and T-carbethoxymethyl-6-nitro BIPS having also methoxy, bromo, or nitro substituents in the 8-position have been recorded. The effects of the substituents on the Xmax and the rate constants are discussed. The preparation of 1-carbethoxy-methylFischer s base is given in detail.112... 

A BIPS having hydrogen rather than alkyl on the l -nitrogen atom could possibly be formed from the reaction between a 2,3,3-trialkylindolenine and a salicylaldehyde. However, the reactions between 4-nitro-2,3,3,7-tetramethylindole-nine and five different substituted salicylaldehydes (3-methoxy-5-nitro 5-nitro 3-bromo-5-nitro 3-nitro-5-methoxy and 3-nitro) gave only the 2-hydroxy(substitu-ted)styryl dyes, which were not solvatochromic or photochromic. The yields were 3-7% based on 5-nitro-2-methylphenylhydrazine, the precursor of the indolenine used. The NMR, UV, and mass spectrometry (MS) evidence excluded spiro or open zwitterionic structures for these products.81... 

The various techniques of Raman spectroscopy have recently been applied to the spiropyrans, and this is discussed more extensively in Chapter 8 in Volume 2. BIPS and its 6-nitro-, 6-nitro-8-methoxy-, and 6-nitro-5,7-methoxy derivatives were studied by surface-enhanced (SERS) and resonance-enhanced Raman spectroscopy in neutral, acidic, and basic solutions. The complex results are too numerous to summarize here, but two unusual ones are that even in acid solutions the tested compounds gave the SERS spectra of the unprotonated open forms, and that an aged solid sample of 6-nitroBIPS gave results very different from a fresh sample. This was attributed to the existence of two enantiomers of the spiro form, which are slowly interconvertible in the solid state and which have greatly different photocoloration quantum yields.167... 

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