Microfocus X-ray diffraction study of the columnar phase of porphyrin-based mesogens

Porphyrin-based materials are prime candidates for solar energy harvesting applications. New compounds incorporating the porphyrin core, which exhibit the columnar liquid crystal (LC) phase, were synthesized as they offer a route to obtaining defect-free large area monodomain films. The structure of the phases exhibited by these materials has been probed by synchrotron X-ray diffraction with a microfocus (14 μm × 14 μm) beam. Exploiting the multidomain nature (i.e., having differently oriented crystal axes) of a thin glass cell, it was possible to obtain complete structural information without the need to have one single macroscopic crystal, which is normally difficult to obtain. The results confirmed the existence of the isotropic, discotic (columnar) LC, and discotic-ordered LC phases in these materials. The optical microscopic work demonstrates how macroscopic control of columnar orientations is achieved by manipulating the LC film thickness, substrate preparation, and the thermal annealing process.