One ring to rule them all: effect of aryl substitution on glass-forming ability in mexylaminotriazine molecular glasses

Mexylaminotriazines are an exciting new class of small molecules capable of forming glassy phases (molecular glasses) that have shown outstanding glass-forming properties and resistance to crystallization. The effect of the structure of the ‘headgroup’ at the 2-position of the triazine ring on glass-forming properties has been studied, but the role of the arylamino substituents is unclear, though it has been shown that one of the aryl groups can be substituted with other aryl groups without loss of glass-forming ability. Herein, a library of mexylaminotriazine derivatives with various arylamino and cycloalkylamino groups has been synthesized and characterized. It was found that glass-forming ability is tolerant to a wide range of substituents, with all the compounds reported being capable of forming glassy phases, and only one compound crystallizing upon heating. On the other hand, the structure of the ancillary group has a profound impact on the glass transition temperatures (Tg) of the compounds, with values ranging from 52 to 131 °C having been obtained. Several trends between substitution pattern and Tg were observed.