TRANSLATIONAL AND ROTATIONAL MOTION OF PROBES IN SUPERCOOLED 1,3,5-TRIS(NAPHTHYL)BENZENE

Measurements of the rotational and translational motion of several pro be molecules in supercooled 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (alpha alpha beta-TNB) are reported. Rotational correlation times from 10(-10) to 10(3) s were measured in the temperature range from 341 to 515 K (T-g = 343.5 K). Translational diffusion coefficients ranged fr om 10(-6) to 10(-15) cm(2)/s over a similar temperature range. The rot ational correlation times of all probes have essentially the same temp erature dependence as the viscosity of TNB. In contrast, the translati onal diffusion of the smallest probe, tetracene, is observed to have a significantly weaker temperature dependence. At T-g, the translationa l diffusion coefficient of tetracene is 300 times larger than expected based on its rotational correlation time. Similar enhancements of tra nslational diffusion near T-g have recently been observed in other gla ss-forming liquids. These observations suggest that dynamics in TNB an d other supercooled liquids are spatially heterogeneous. The probes us ed in this study were tetracene, rubrene, 9,10-diphenylanthracene, and 9,10-bis(phenylethynyl)anthracene.