BODIPY-Conjugated Thermoresponsive Copolymer as a Fluorescent Thermometer Based on Polymer Microviscosity

Research Center for Solar Energy Chemistry and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan.
Langmuir (Impact Factor: 4.46). 10/2009; 25(22):13176-82. DOI: 10.1021/la901860x
Source: PubMed


A simple copolymer, poly(NIPAM-co-BODIPY), consisting of N-isopropylacrylamide (NIPAM) and boradiazaindacene (BODIPY) units, behaves as a fluorescent thermometer in water. The copolymer exhibits weak fluorescence at <23 degrees C, but the intensity increases with a rise in temperature up to 35 degrees C, enabling an accurate indication of the solution temperature at 23-35 degrees C. The heat-induced fluorescence enhancement is driven by an increase in the polymer microviscosity, associated with a phase transition of the polymer from the coil to globule state. The viscous domain formed inside the globule-state polymer suppresses the rotation of the meso-pyridinium group of the excited-state BODIPY units, resulting in heat-induced fluorescence enhancement. The polymer shows reversible fluorescence enhancement/quenching regardless of the heating/cooling process and displays high reusability with a simple recovery process.

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    • "Accordingly, the ICG molecules inside the NPs are exposed to a polymer-rich microenvironment, which has a relatively lower polarity and higher viscosity compared with the water-rich microenvironment. This type of microenvironment can suppress the nonradiative decay rate of the excited fluorophores2425, and therefore the fluorescence intensity from the ICG increases dramatically. This phase transition caused by the environment's temperature crossing LCST is reversible. "
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    • "This relationship has been experimentally shown to be valid in a wide range of viscosities and in both polar and nonpolar fluids [15,34,40,54,55], although deviations exist particularly in the low-viscosity regime that need additional interpretation. Equation 1 has become so popular that in some instances the existence of this power-law relationship has been used to purport TICT behavior of specific molecules [56-59]. "
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