Halogen-containing bridged carborane–tetraphenylethene compounds: efficient and wide-range shifted excitation-dependent emissions

Abstract

Halogen-containing bridged carborane–tetraphenylethene compounds have been synthesized by the chlorination of the corresponding tetraphenylethene–carboranylmethanol. The fluorinated compound 1 shows interesting excitation-dependent emission (ex-de) properties in various aggregate states, i.e. powder before and after grinding, ground-fuming and ground-annealing, whereas the non-fluorinated analog compound 2 displays ex-de properties only after grinding. The carborane cluster, bridging group and halogen atoms cooperatively tune the emission properties of these compounds. Compound 1 has good crystallinity and multiple interactions in the molecular packing, thus in various aggregate states a mixture of crystalline and amorphous particles in an uncertain ratio renders the samples the corresponding ex-de properties, and compound 2 shows ex-de properties due to a similar reason. Compounds 1 and 2 exhibit typical aggregation-induced emission properties as they have tetraphenylethene moieties, and good photoluminescence quantum yields in the solid state (0.54, 1; 0.39, 2) being relatively high when compared to those of the reported carborane derivatives with ex-de properties. In addition, compound 1 shows a relatively wide-range emission wavelength shift (maximum 73 nm) at various excitation wavelengths. These results suggest a new convenient approach to synthesize various compounds with ex-de properties.