Fulgides isomers

Thus, X-ray crystallography has been used to establish the geometry of the fulgide isomers and to demonstrate the strain in the molecular structure which results in restricted rotation about the single bond and extended bond angles. 

H. D. Ilge, Photochemistry of phenyl fulgides. XX. Absence of activation barriers for photoisomerization reactions in the excited singlet state of extremely sterically hindered a, 8-di-(4-alkoxypheny 1) fulgide isomers, J. Photochem., 33, 333-347 (1986). 

Fulgides can exist as or Z isomers by rotation around the double bonds in (1.33). This is illustrated for the furano derivative in Figure 1.10. Isomerisation of the yellow Z-fulgide (1.34) to the fi-fulgide (1.35) and cyclisation of this to the red coloured photochrome (1.36), designated as C here but often called the P state, occurs on irra-... 

The corresponding imides (1.40), called fulgimides, are most readily synthesised by conversion of the fulgide into the succinamic acids by reaction with amines, followed by dehydration. Functionalisation of the anhydride can also be achieved by reaction of the fulgides with malononitrile in the presence of diethylamine and subsequent recyclisation with acetyl chloride to give (1.41) from the corresponding E-fulgide and (1.42) from the Z-isomer. 

At least one of the four substituent groups on the fulgide is an aromatic ring, for example, a phenyl group. The structure of the fulgide is skillfully constructed as a hexatriene unit that has two different isomers, a Z form 0) and an E form (4) based on the a,p-unsaturated double bond, R3 and R4 being the same. 

A fulgenolide is a kind of lactone. When R2 is an aromatic group, only the L isomer (9) has photochromic behavior. Fulgenates have excellent photochromic properties, but the absorption band is blue shifted compared with that of the corresponding fulgide. 

Fulgide 1 with four different groups R -R, of which at least one group is aryl, can exist as four geometrical isomers. There are two conventions in use for... 

Since a fulgide, its E, Z isomers, and photocyclized form exhibit different absorption spectra, electronic absorption spectra are often used to investigate the photoreaction of fulgides. The UV absorption spectra data of some aryl lulgides are listed in Table 4.1. 

The R group had little effect on the absorption maximum (Zmax) and molar absorption coefficient (emax) of fulgides and 7,7a-DHBF derivatives. The absoprtion maxima of E isomers were about 348 nm, which is about 10 nm shorter than those... 

The X-ray structure of two isomers of fulgide 35 have been determined by Yoshioka et al.56 In the E form, the succinic anhydride and the furyl ring were not coplanar and were considerably twisted relative to each other. This is due to the steric hindrance effect between the isopropylidene group and the 2-methyl group in the furyl moiety. The distance between the two reactive sites, which corresponds to the chemical bond formed during photocyclization, was 3.44 A. 

The general formula for fulgides is represented as compound 1. Based on the absorption spectra data, 1-3 fulgide systems can be separated into two largely independent cinnamic anhydride-type chromophores. Freudenberg eta/.101 studied the absorption spectra of ethyl /rans-cinnamate 82 and diethyl-(E,E)-bisbenzylidene succinate 83 and found that the absorption spectrum of compound 83 was similar to that of compound 82, rather than 1,4-diphenylbutadiene. This indicated that compound 83 had two relatively independent chromophores, which was supported by Heller and Szewczyk.16 They demonstrated that the UV spectrum of (E,E)-bis-(a-phenylethylidene) succinic anhydride It was almost identical with a 1 1 mixture of (E,Z) and (E,E) isomers of the same fulgide. 

J. C. A. Boeyens, L. Denner, and G. W. Perold, Rotamers and isomers in the fulgide series. Part 2. Stereochemistry and conformational analysis of bis-(j>methoxybenzylidene) succinic anhydrides by X-ray crystallography and molecular mechanics, J. Chem. Soc., Perkin. Trans. 2, 1988, 1999— 2005. 

The Aberchrome 540 actinometer (21) is based on the reversible photocyclization of the pale yellow furyl fulgide, I in Eq. (17), to its deep-red cyclized isomer (II), i.e.. 

Figure 6. Thermal stability at 80°C of the closed-ring isomers of fulgide derivatives (15-20 wt. % in PMMA film).

The blue isomer obtained by irradiation of the well-known photochromic compound 2-(2,4-dinitrobenzyl)pyridine has been identified as the enamine (36) (More O Ferrall and Quirke). There has been a resurgence of interest in photochromic fulgides see e.g. Suzuki et al. Wilcox et al. have de bribed a new photolabile protecting group for amino-acids. An interesting example of intramolecular oxetane formation has been provided by the photoisomerization of indole (37) to (38) (Takechi et al.). 

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