Frank-Kasper phases in charge transfer complexes enable tunable photoelectronic properties.

Abstract

Understanding how particles pack in space and the mechanisms underlying symmetry selection across soft matter is challenging. The Frank-Kasper (F-K) phase of complex spherical packing is amongst the most fascinating phases; however, it has not been observed in discotic liquid crystals until now. Herein, we report the first observation of F-K phases of charge transfer complexes (CTCs) obtained from triphenylene derivatives as donors and 2,4,7-trinitro-9-fluorenone as the acceptor. The CTCs were characterized using experimental and theoretical calculations, indicating that the F-K A15 cubic lattice possesses a unit cell containing 8 sphere-like supramolecules, each of which was self-assembled from 3 CTC complexes. The lattice constant was only 3.2 nm, which is by far the smallest for the A15 phase. Interestingly, the supramolecular assembly can be regarded as the molecular column splitting into isolated spherical fragments, impeding charge transfer and turning it into one insulator. This provides a simple and effective method for preparing asymmetric complex compounds for the design of unconventional self-assembled nanostructures.