Bridged o-carborane–anthracene dyads as dual state emission luminogens: synthesis, characterization, and mechanochromic properties

Abstract

Dual state emission (DSE) compounds emit light both in solution and in the solid state and have wide potential applications; however, their design and synthesis are challenging. Herein two bridged carborane–anthracene dyads with DSE properties are reported. The reduction of carboranyl Schiff base 9-anthracenylidene-1-amino-o-carborane (1) with NaBH₄ affords compound 2. The photophysical properties and mechanochromism of both compounds and the corresponding silica gel composites were studied. The carborane cage can adjust the optical properties of the two compounds to a different extent. Because of the D–π–A structure, compound 1 exhibits intramolecular charge transfter (ICT) characteristics in the absorption and emission spectra, and aggregation-induced emission enhancement (AIEE) in MeCN–H₂O, whereas compound 2 shows absorption and emission properties (in solution) characteristic of the anthracene moiety, and excimer emissions in THF–H₂O (water content 98%) and in the crystalline state. The multiple π⋯π interactions of anthracenes lead to supramolecular tetramers in the crystal of 2 that make the excimer emission possible. In terms of stimulus responsiveness, both compounds exhibit blue shifted emissions with grinding, displaying mechanochromic properties. The corresponding silica gel composites show different emission properties from the solid samples. This work provides a simple strategy for the design and synthesis of novel carborane-containing DSE compounds and solid-state luminescence regulation for potential applications.