Measurement of glass-transition temperature of thermoreversible photochromic materials based on mechanochemical amorphization

Abstract Photochromic diarylethene (DAE) materials are expected to be applied to various organic devices, and it is important to measure the glass transition temperature (Tg) in order to evaluate their stability. Although DAEs have excellent thermal stability, their colored state has a high melting point, and either a thermal cyclo-reversion reaction or decomposition occurs during the differential scanning calorimetry (DSC) measurement. Tgs in the colored state, therefore, are hard to measure. In this study, we succeeded in measuring Tgs of the colored state with DSC by preparing the colored amorphous state based on a mechanochemical effect for various DAEs. In addition, the relationship between the isomerization ratio and Tg was determined by combining the amorphization and the thermal reversion reaction near the melting point. It was found that Tg changed monotonically according to the isomerization ratio.