Photoswitching Using an Array of Photochromic Molecules

Compound 24(00) underwent photochromic reaction by alternate irradiation with UV and visible light. Upon irradiation of the ethyl acetate solution of 24(00) with 313-nm light, an absorption at 560 nm appeared, as shown in Fig. 9.10. This absorption grew and shifted and the system reached the photostation-ary state after 120 min. The color of the solution changed from pale blue to red-purple and then to blue-purple. Such a red spectral shift suggests the formation of 24(CC). The isosbestic point was maintained at an initial stage of irradiation, 

ESR spectra of isolated 24(00), 24(CO) and 24(CC) were measured in benzene at room temperature as shown in Fig. 9.11. The spectra of 24(00) and 24(CO) are five-line spectra, suggesting that the exchange interaction between the two nitro-nyl nitroxide radicals is much weaker than the hyperfine coupling constant (2//kB 3 X 10 3 K). 

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