Controllable π-π coupling of intramolecular dimer models in aggregated states.

π-π coupling as a common interaction plays a key role in emissions, transport and mechanical properties of organic materials. However, the precise control of π-π coupling is still challenging owing to the possible interference from other intermolecular interactions in the aggregated state, usually resulting in uncontrollable emission properties. Herein, with the rational construction of intramolecular dimer models and crystal engineering, π-π coupling can be subtly modulated by conformation variation with balanced π-π and π-solvent interactions and visualized by green-to-blue emission switching. Moreover, it can rapidly respond to temperature, pressure and mechanical force, affording a facile way to modulate π-π coupling in situ . This work contributes to a deeper understanding of the internal mechanism of molecular motions in aggregated states.