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Journal Article
Excited-State Intramolecular Proton Transfer on 2-(2′-hydroxy-4′-R-phenyl)Benzothiazole Nanoparticles and Fluorescence Wavelength Depending on Substituent and Temperature
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- Authors
- Yong Hee Kim, Soo-Gyun Roh, Sang-Don Jung, Myung-Ae Chung, Hwan Kyu Kim, Dae Won Cho
- Issue Date
- 2010-03
- Citation
- Photochemical & Photobiological Sciences, v.9, no.5, pp.722-729
- ISSN
- 1474-905X
- Publisher
- Royal Society of Chemistry (RSC)
- Language
- English
- Type
- Journal Article
- Abstract
- The fluorescence emission properties of 2-(2??-hydroxy-4??-R- phenyl)benzothiazole (HBT-R) nanoparticles with different substituents (R = -COOH, -H, -CH3, -OH, and -OCH3) were investigated using spectroscopic and theoretical methods. HBT-Rs displayed dual enol and keto (excited-state intramolecular proton transfer (ESIPT)) emissions in nonpolar solvents. The spectral change of their ESIPT emissions was affected differently by the electron donating (or withdrawing) power of the substituents; a bathochromic shift for the electron donating group and a hypsochromic shift in electron withdrawing group. In addition, the changes in energy levels calculated by the ab initio method were consistent with the spectral shifts of HBT-R in solution. We prepared aggregated HBT-R nanoparticles using a simple reprecipitation process in tetrahydrofuran-water solvents. The ESIPT emission of aggregated HBT-R nanoparticles was strongly enhanced (over 45 times) compared to those of monomer HBT-Rs in toluene, as markedly shifted ESIPT emissions are observed at longer wavelength without any quenching by self-absorption. Aggregated HBT-R nanoparticles showed longer lifetimes than those of monomer molecules. The temperature effect on the aqueous dispersion of the aggregated HBT-R nanoparticles was also explored. It shows a fluorescent ratiometric change in a range of temperature from 7 to 65 °C. A mechanism of a temperature-dependent equilibrium between the nanoparticles and the solvated enols is proposed for the emission color change. © 2010 The Royal Society of Chemistry and Owner Societies.
- KSP Keywords
- Ab initio method, Aqueous dispersion, Bathochromic shift, ESIPT emission, Electron donating group, Emission properties, Energy level, Hypsochromic shift, Nonpolar solvents, Self-absorption, Spectral shift