Stiff-stilbene derivatives as new bright fluorophores with aggregation-induced emission

Stiff-stilbene derivatives have been widely explored as molecular rotors, molecular force probes and optical switches with excellent performance. However, their function as fluorophores is poorly understood. In the present work, we design three stiffstilbene derivatives and study their photophysical properties. These compounds exhibit very weak emission in solution but significantly enhanced monomer emission in viscous solvent, bright excimer emission in aggregates and at solid state. Detailed spectroscopic studies, single crystal structural analysis, powder X-ray diffraction (XRD) as well as effects of substituents have been carefully examined. They provide direct evidence that intermolecular interactions and molecular packing, which can restrict bond vibration and rotation, are responsible for the bright aggregation-induced emission.