Facile synthesis, aggregation-induced emission, mechano- and thermochromism of o-carborane–tetraphenylethene dyads with a short CH(OH) linker

Abstract

It is of interest to fine tune the luminescence properties of organic luminophores by using the three-dimensional carborane cluster. In this work, o-carborane–tetraphenylethene compounds 1–4 with a short CH(OH) linker have been synthesized via the reactions of o-carborane and tetraphenylethene-based aldehydes in the presence of tetrabutylammonium fluoride, and their structures, luminescence and stimuli-responsive properties have been investigated. As expected, the products show aggregation-induced emission (AIE) properties due to the typical AIE-active tetraphenylethene (TPE) moiety. The carborane and hydroxyl group on the linker have great effects on the solid state structures and properties of the products. The emission maxima of the compounds (1: 426, 2: 437, 3: 440, 4: 445 nm) are essentially the same as that of the parent TPE (439–445 nm) in the solid state, whereas all the carborane–TPEs reported show red-shifted emissions (452–678 nm), and the luminescence quantum yields (1: 0.25, 2: 0.17, 3: 0.32, 4: 0.30) are higher than that of TPE (0.23). In addition, 1–4 show mechano- and thermofluorochromic properties. The silica gel composites of 1–4 exhibit higher luminescence thermal stability, with the T_50% (the temperature at which the luminescence intensity reaches 50% of that at low temperature) being greater than 120 °C, higher than the solid samples and the silica gel composite of TPE. These results indicate that carborane and a suitable linker could play a unique role in precisely regulating the emitting properties of TPE-type compounds.