High Fluorescence Efficiencies and Large Stokes Shifts of Folded Fluorophores Consisting of a Pair of Alkenyl-Tethered, π-Stacked Oligo-<i>p</i>-phenylenes

A series of pure hydrocarbon fluorophores containing a pair of π-stacked oligo-p-phenylenes have been synthesized and analyzed by NMR and X-ray crystallography. They show good fluorescence in solutions and enhanced fluorescence in the aggregated state. Large Stokes shifts (up to 214 nm) have been achieved in these folded fluorophores in virtue of intramolecular energy transfer, and balanced structural rigidity and flexibility. These folded fluorophores provide perfect models for understanding the energy and charge transfer process in π-stacked systems.