Topology switch between AIE and ACQ: a balance of substituents

Intermolecular interactions appearing in solution, aggregates and solid state are known to affect the photophysical properties of fluorophores, leading either to emission quenching or to emission enhancement upon aggregation. The novel strategy for the aggregation-induced fluorescence change based upon the subtle balance of the intermolecular and intramolecular charge transfer in the benzothiazole derivatives is presented here, leading to the extremely bright aggregates of the compounds dark in solution or vice versa. The introduction of the two different mild substituents into the fluorophore core results in two regioisomers exhibiting the same crystal packing, but extremely different behavior upon aggregation. Such an approach opens a simple way of controlling the AIE/ACQ behavior of small molecules in the wide range of FQY values.