Analytical Sciences

Microviscosity of Supercooled Water Confined within Aminopropyl-modified Mesoporous Silica as Studied by Time-resolved Fluorescence Spectroscopy

Akira YAMAGUCHI,* Manato NAMEKAWA,** Tetsuji ITOH,*** and Norio TERAMAE**

*College of Science and Frontier Research Center for Applied Atomic Sciences, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
**Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
***Research Center for Compact Chemical System, National Institute of Advanced Industrial Science and Technology (AIST), Nigatake 4-2-1, Miyagino, Sendai 983-8551, Japan

The fluorescence dynamics of rhodamine B (RhB) immobilized on the pore surface of aminopropyl (AP)-modified mesoporous silica (diameter of the silica framework, 3.1 nm) was examined at temperatures between 293 and 193 K to study the microviscosity of supercooled water confined inside the pores. The mesoporous silica specimen with a dense AP layer (2.1 molecules nm⁻²) was prepared, and RhB isothiocyanate was covalently bound to part of the surface AP groups. The fluorescence lifetime of the surface RhB increased with decreasing temperature from 293 to 223 K, indicating that freezing of the confined water did not occur in this temperature range. The microviscosity of the supercooled confined water was evaluated from an analysis of the lifetime data based on a frequency-dependent friction model.

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