Correlation of Structure with Crystalline to Amorphous Phase Transitions of 1,3,6-Substituted Fulvene-Derived Molecular Glasses

An
investigation into the crystalline to amorphous phase transitions
of prepared 1,3,6-substituted pentafulvenes showed the expected reversible
heated melt and cooling recrystallization in only a few examples.
Systematic incorporation of bulky substituents at the 6-position of
the fulvene ring led to the nonreversible thermal behavior, rendering
phases that were locked into glassy, vitrified states. These molecular
glasses produced physically translucent and amorphous features with
glass transition temperatures in the range of 61–77 °C,
comparable with high-strength plastics such as polyethylene terephthalate.
Additionally, the melting point transitions and the resulting heat
of fusion values were found to be directly influenced by the nature
of the 6-position substituent. Single crystal X-ray crystallography
showed that in some cases, fulvenes possessing fused aromatics exhibited
a high degree of intermolecular π–π stacking. These
results point to a class of molecular glass formers as host materials
possessing tunable bulk properties for potentially new optical applications.