C O M M U N I C A T I O N S
PNiPAAM is not pH dependent25 and semiempirical measurements
of the dipole moment gave a dipole moment of 4.005 D for the
protonated dye in comparison to 10.715 D for the betainic dye.
According to this, the protonated dye is less polar than the betainic
dye. Thus, the LCST decreases more strongly with increasing
amount of the protonated dye in copolymer 6.
In conclusion, we prepared a colored copolymer 6 with LCST
behavior that represents an interesting type of environmental
sensitive material. It is possible to change the color of this
copolymer via pH, type of solvent, temperature, and host-guest
interaction with cyclodextrin. Actually, these effects are completely
reversible. Therefore, the behavior of this new polymer-attached
solvatochromic dye as an optical sensor in solution and in bulk
may be useful for the development of new intelligent signal
materials.
Figure 1. Transmittance (τ) of a solution of polymer 6 in water (5 mg/
mL) at pH 10 versus temperature during heating and cooling.
Supporting Information Available: Experimental preparations and
analysis for 3, 4, 5, and 6 and maximal absorbance of copolymer 6.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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Figure 2. Color effects of copolymer 6 at pH 1 (no shift) and at pH 10
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J. AM. CHEM. SOC. VOL. 129, NO. 12, 2007 3503