Fig. 7: Perspective shift from covalent bonds in molecules to non-covalent interactions in aggregates.
From: Emergent clusteroluminescence from nonemissive molecules
a When the chromogenic units (e.g., the phenyl rings in biphenyl or the nitrogen atoms in pentazole) are directly linked together, the involved π and lone-pair electrons are delocalized via the TBC (through-bond conjugation). b When the chromogenic units (e.g., the phenyl groups in the dibenzenacyclohexaphane ring or the oxygen atoms in the same xylose molecule) are separated by the covalent bonds in between, the electron clouds can be overlapped via the intramolecular TSI (through-space interaction). In non-covalently bonded systems, the chromogenic units (e.g., the oxygen atoms in the different xylose molecules in the monosaccharide aggregate or the platinum ions in the different BaPt(CN)4 salts in the inorganic crystal) can experience strong intermolecular TSI (through-space interaction). c Examples illustrating the critical importance of non-covalent interactions in physical and life sciences. Left panel: aggregation can turn a non-luminescent molecule (DFB-TPE) luminescent, and different non-covalent interactions can produce different aggregates with varying colors of emission: Xtal-Y, Xtal-G, and Xtal-O (crystals emitting yellow, green, and orange lights, respectively). Right panel: life is a living system of biomolecule aggregates. Above the molecular level, the hierarchical structures of the living aggregates (e.g., α-helix, triple helix, microfibril, fibril, fasciculus, muscle belly, and tendon) are mainly determined by the non-covalent interactions at all the structural levels. c is adapted with permission from ref. 94 Copyright (2020) The Royal Society of Chemistry and the Chinese Chemical Society.
