Fulgide derivatives

Isofulgimides were also introduced by Heller etal.3 in 1993. An isofulgimide is a fulgide derivative in which one of the oxygens in the carbonyl group of the anhydride ring of the fulgide is replaced by a substituted imino, as shown in compounds 6 and 7. 

Thienyl fulgide (in PS) can be colored and bleached at all temperatures between 300 and 10 K. The coloring reaction does not require thermal activation, but for the bleaching process a small activation barrier (50 cm 1) exists. Further studies on the photoreaction kinetics of thienyl fulgide derivatives (49a-49c) have been carried out by the same research group,59 as shown in Scheme 14. 

J. Hibino and E. Ando, Photochromic fulgide derivatives, Jpn. Kokai Tokyo Koho JP, 62,242,677 (Chem. Abstr. 109, 14838k). 

Another defect of fulgide derivatives is solvolysis. The maleic anhydride structure is destroyed in alcohols or protic solvents. To avoid such solvolysis the maleic anhydride structures were changed to maleimides the maleimide derivatives were stable in alcohol solutions. 

Upon UV irradiation the furyl fulgide undergoes not only cyclization but also an E-Z photoisomerization reaction (Scheme 6). The ratio between the cyclization and the E-Z isomerization depends on the steric hindrance of substituent R. Furyl fulgide derivatives with various R substituents were prepared and the quantum yields were compared [31-34]. The results are summarized in Table 4. 

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

Figure 7. Fatigue resistance of fulgide derivatives a) in toluene and b) in PMMA film. Aq and A were the absorbances of the first cycle and after n coloration/decoloration cycles, respectively.

Table 4. Quantum yields of furyl fulgide derivatives in toluene.

The contribution of computational chemistry to the study of mechanistic problems in photochromism is increasing since information on intermediates, transition states, and conical intersections is often very difficult to obtain experimentally. As a list of all such studies is beyond the scope of the present chapter, our discussion will focus on representative molecules such as spiropyran derivatives and fulgide derivatives, but will also include examples of other recent work. 

Sagisaka T, Yokoyama Y. 2000. Reversible control of the pitch of cholesteric liquid crystals by photochromism of chiral fulgide derivatives. Bull Chem Soc Jpn 73(1) 191 196. 

Y. Yokoyama, T. Sagisaka, Reversible control of pitch of induced cholesteric liquid crystal by optically active photochromic fulgide derivatives. Chem. Lett. 687-688 (1997)... 

Fulgide derivatives have been widely used as photocontrol-lable units for the design of supramolecular switches. The photochromism of these components occurs between one of the colorless open form and the photocyclized colored form. Fulgides are not luminescent, at room temperature, unless... 

Inada, X, Uchida, S., and Yokoyama, Y, Perfect on/ofF switching oF emission oF fluorescence by photochromic reaction oF a binaphthol-condensed Fulgide derivative, Chem. Lett., 321, 1997. Chem. Lett., 961,1997. 

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