330
K. Higashiguchi and K. Matsuda
Scheme 19.2 Syntheses of the asymmetric amphiphilic diarylethenes by C–H arylation
25, and 27% for compounds 1, 2, and 3, respectively. Symmetric compounds were
also produced as by-products, but the target compounds were easily purified due to
significant difference in polarity.
19.2.1 Photoinduced LCST Transition
The change in the absorption spectrum with photoisomerization indicated different
behavior for a solution and a suspension. Compound 1 showed ordinary
photochromism in an acetonitrile solution, i.e., a colorless solution of 1a turned
blue upon irradiation with UV light (1b) and turned back to being colorless upon
subsequent irradiation with visible light (Fig. 19.1a). On the other hand, the aqueous
suspension displayed a two-step change in the absorption spectrum. Initial whiteturbid suspension turned to a blue suspension upon short irradiation with UV light.
The absorption band shifted to shorter wavelengths and the color changed to reddish
0
0.2
0.4
0.6
0.8
1.0
300
400
500
600
700
800
O.D.
Wavelength / nm
UV
0
0.1
0.2
0.3
0.4
0.5
0.6
300
400
500
600
700
800
Absorbance
Wavelength / nm
UV
(a)
(b)
Fig. 19.1 Spectral changes along with photoisomerization from 1a to 1b upon irradiation with UV
light in a acetonitrile solution and b aqueous suspension. Adapted with permission from Ref. [10].
Copyright 2015 American Chemical Society