PHOSPHORESCENCE PROBES OF THE GLASSY STATE IN AMORPHOUS SUCROSE

We have used phosphorescence from the luminescent chromophores N-acety ltryptophanamide (NATA) and erythrosin B (Ery B) to probe the molecula r dynamics of the glassy state and the glass-to-rubber transition in a morphous sucrose. These measurements exploit the known sensitivity of phosphorescence intensity to the rate and extent of molecular collisio ns with the local environment. Both probes exhibit intense, well-defin ed phosphorescence emission spectra in the glassy sugar matrix. Time-r esolved phosphorescence intensity decays for each probe were multiexpo nential both above and below the glass transition temperature, indicat ing that the sucrose matrix is heterogeneous on the molecular level; l ocal microviscosities around the NATA probe were estimated in the rang e from 10(4) to 5 x 10(7) Pa . s in the glassy state at 25 degrees C. Plots of phosphorescence Lifetime versus temperature for both probes a re linear above and below the glass transition temperature of sucrose (62 degrees C), but exhibit a break in slope near approximately 50 deg rees C characteristic of a dramatic change in the rate of molecular co llision between the probe and the local environment. The similar sensi tivity of two chemically different spectroscopic probes (the indole ri ng of NATA and the xanthene ring of Ery B) to molecular changes near t he glass transition in this sugar indicates that phosphorescence may p rovide a generally applicable, site-specific probe of the glassy state and changes in it in biological materials.