Dynamical Heterogeneity in Glassy o-Terphenyl:  Manifestation of Environment Changes in Photoisomerization Kinetics of Probe Molecules

Abstract

A new method for the investigation of dynamical heterogeneity in glassy matrixes is presented and illustrated by the example of o-terphenyl (OTP). UV-vis absorption spectroscopy has been used to monitor the cis-trans isomerization kinetics of probe molecules in glassy OTP. The dependence of isomerization quantum yield on light intensity has been established. This dependence is shown to be due to the change in the local environment of the probe molecules. The simple model is suggested to estimate the time required for the environment to change, tauex. The tauex values from 2.6 x 10(2) to 1.9 x 10(5) s have been obtained for environments of molecules of 1-naphthylazomethoxybenzene (NAMB) in OTP over a temperature range from 244 to 204 K (Tg+1 to Tg-39 K). The temperature dependence of exchange time has a non-Arrhenius character. As the temperature decreases, an increase in exchange time slows down. The activation energy of the relaxation process is 54 kJ/mol over the range of 224-239 K.

Supercooled Liquid Dynamics: Advances and Challenges

“…Experimentally, no homogeneous case with η ≈ 0 has been found, and the majority of findings are consistent with pure heterogeneity in the sense of β intr = 1 or η = 1. Due to the variety of techniques applied, heterogeneous dynamics with η ≈ 1 have been observed across a wide range of temperatures, from sub T g , to beyond T c , corresponding to timescales between >1000 s [182] and 6 ns [183].…”

Dynamical Heterogeneity in Glassy o-Terphenyl. 2. Measurement of Environment Structure Lifetime Using Reversible Reactions

“…The error bars represent one standard deviation. The figure shows also the previous data on the exchange time measured using variable light intensity method 60 and the time of NAMB molecules rotation. 63 The figure demonstrates the close agreement of all the values.…”

“…The experimental technique has been fully described elsewhere. 60 Here, we just mention the most important details.…”

“…Empty circles, data estimated using the model described in the text; crosses, data estimated from the time dependence of τ KWW ; filled circles, data from the work. 60 Also the rotation times 63 are shown (triangles). Using the method of multidimensional NMR it has been established that the exchange times in PVA 21 and polystyrene 44 are comparable with the reorientation times of polymeric segments at the temperature slightly exceeding T g .…”

“…Earlier, in the same system (NAMB/OTP) the lifetime of environment nearby the cis particles whose quantum yield of cisftrans isomerization is lower than average have been measured below T g . 60 It is interesting to compare the new data with the previous ones.…”