Fluorescence properties of hemicyanine in the nanoporous materials with varying pore sizes

Hemicyanine dye molecules were put into the nanoporous materials (silicalite-1, zeolite-beta, and MCM-41) with different pore sizes. Fluorescence anisotropy measured from these systems indicated that the incorporated dye molecules were well-aligned along the straight channel of the zeolite pores, except for dye molecules in the largest pores of MCM-41. The fluorescence decay lifetimes were 2.1, 1.7, and 1.1 ns, for the dyes in silicalite-1, zeolite-beta, and MCM-41, respectively. Significant increase in the fluorescence intensity and the fluorescence decay lifetime was observed with the decrease of the pore size. This was due to intramolecular rotational motion of the dye molecules more hindered in smaller pores, demonstrating the fluorescence properties of the dye molecule can be controlled at will by the choice of zeolite matrix.