Switching between intramolecular charge transfer and excimer emissions in solids based on aryl-modified ethynyl?o-carboranes

Because of its unique electronic properties, o-carborane has attracted attention as a scaffold for constructing solid-state luminescent materials. Here, we report stimulus-responsive luminochromic materials based on polycyclic aromatic hydrocarbon (PAH), such anthracene and pyrene, modified with the ethynyl-o-carborane unit. Initially, luminochromism originating from switching different emission mechanisms is described between intramolecular charge transfer (ICT) excimer triggered by mechanical stimuli, heat, vapor annealing regarding single o-carborane-substituted anthracene. Next, luminescence properties two ethynyl-o-carboranes at both ends PAHs are presented. In particular, multi-step mechanochromic pyrene derivative explained. Stepwisely changes weak stimuli that can induce cracking sites, followed behavior grinding treatment, which causes phase transition crystal to amorphous, leading mechanism ICT emission.