Design of a homologous series of molecular glassformers.

We design and synthesize a set of homologous organic molecules by taking advantage of facile and tailorable Suzuki cross coupling reactions to produce triarylbenzene derivatives. By adjusting the number and the arrangement of conjugated rings, the identity of heteroatoms, lengths of fluorinated alkyl chains, and other interaction parameters, we create a library of glassformers with a wide range of properties. Measurements of the glass transition temperature (T) show a power-law relationship between T and molecular weight (M), with of the molecules, with an exponent of 0.3 ± 0.1, for T values spanning a range of 300-450 K. The trends in indices of refraction and expansion coefficients indicate a general increase in the glass density with M, consistent with the trends observed in T variations. A notable exception to these trends was observed with the addition of alkyl and fluorinated alkyl groups, which significantly reduced T and increased the dynamical fragility (which is otherwise insensitive to M). This is an indication of reduced density and increased packing frustrations in these systems, which is also corroborated by the observations of the decreasing index of refraction with increasing length of these groups. These data were used to launch a new database for glassforming materials, glass.apps.sas.upenn.edu.