Regulating and Predicting the Polyhedral Crystal Morphology in Spirofluorene Molecular Systems

Crystallization of organic steric molecules often leads to multiple polyhedral crystal morphologies. However, the relationships among the molecular structure, supramolecular interaction, aggregation mode and crystal morphology are still unclear. In this work, we elaborate two model crystals formed by spiro[fluorene-9,9'-xanthene] (SFX) and spiro[cyclopenta[1,2-b : 5,4-b']dipyridine-5,9'-xanthene] (SDAFX) to demonstrate the feasibility of morphology prediction by periodic bond chain (PBC) theory based on interaction energy (IE) values in terms of single point energy. With non-directional van der Waals forces, only one PBC direction is found in SFX crystal, leading to the irregular 1D rod-like structure. Compared with SFX, the extra N heteroatoms in SDAFX can bring additional hydrogen bonds and some other interactions into the bulky molecular skeletons, inducing 3-dimensionally oriented PBCs to form the explicit F-face network in SDAFX which leads to the final octahedral structure. A simple and accurate method has been provided to quantify PBC vector on the supramolecular level in the organic molecular system, and the PBC theory has also been further demonstrated and developed in the morphology prediction of organic spiro-molecules.