Axial Chiral Bisbenzophenazines: Solid-State Self-Assembly via Halide Hydrogen Bonds Triggered by Linear Alkanes

An axial chiral tetrachlorinated
bisbenzo­[a]­phenazine has been discovered that undergoes
an alkane-induced shift in the solid state from a disordered amorphous
form to an ordered polycrystalline form. This phase transition is
caused by the formation of pores that accommodate linear alkanes of
varying lengths with a very strong affinity as judged by differential
scanning calorimetry. Single crystal X-ray structure analysis revealed
that a series of weak phenolic OH···Cl hydrogen bonds
dictates the pore structure. These weak interactions can be disrupted
mechanically, causing the material to revert to the amorphous form.
Notably, the interchange between the amorphous and crystalline forms
is readily reversible and is easily observed by characteristic colorimetric
changes. Measurements via photoimage processing reveal that the degree
of color change is dictated by the type of alkane employed.