Aggregation-responsive ON–OFF–ON fluorescence-switching behaviour of twisted tetrakis(benzo[b]furyl)ethene made by hafnium-mediated McMurry coupling

Abstract

Fluorescence-switching dyes serve as important tools for bioimaging and environment sensing. Herein, we report a new type of molecule, tetrakis(benzo[b]furyl)ethene (TBFE), that undergoes two-wavelength ON–OFF–ON three-stage fluorescence switching triggered by aggregation. This compound features a sterically hindered tetrasubstituted ethene, made available by a hafnium-mediated McMurry coupling reaction. A fluorescent band of TBFE at 360 nm in THF disappears upon dilution with water towards 40% water in THF, giving way to a new peak at 510 nm. This switching behaviour is attributed to the combination of THF/H₂O ratio-dependent aggregation-caused quenching and aggregation-induced emission, as supported by the change of size distribution measured by dynamic light scattering and scanning electron microscopy.