Toward Crystalline Molecular Rotors with Linearly Conjugated Diethynyl-Phenylene Rotators and Pentiptycene Stators

A strategy for the construction of crystalline molecular
rotors
involves the assemblage of chemical structures that emulate the elements
of macroscopic rotary devices, such as those found in macroscopic
gyroscopes and compasses. In this report, we describe an efficient
and short synthetic route for preparation of molecular rotors with
two pentiptycene-units linked at their central benzene ring by triple
bonds to a linearly conjugated phenylene rotator. Five analogous compounds
with phenol, alkoxy, or alkoxycarbonyl substituents were synthesized
and fully characterized in solution and in the solid-state through
various methods, such as cross-polarization magic angle spinning (CPMAS) 13C NMR and single crystal X-ray diffraction. Molecular and
packing structures obtained from single crystal X-ray diffraction
and crystallization properties were analyzed with the goal of identifying
the key parameters that may hinder or facilitate the formation of
dynamically functional, crystalline molecular rotors.