Solid-State Thermochromic Luminescence through Twisted Intramolecular Charge Transfer and Excimer Formation of a Carborane-Pyrene Dyad with an Ethynyl Spacer

The pyrene-tethered carborane CBEP, which exhibited rapid and dramatic luminochromism, was synthesized. Based on optical measurements, we found that CBEP exhibited orange emission at room temperature, which was caused by intramolecular charge transfer in the solid state, and green excimer emission at 77K. We proposed that excimer formation could be encouraged by introducing a small amount of steric hindrance with an ethynyl spacer group. We found that o-carborane could suppress aggregation-caused quenching without the inhibition of excimer formation because of this steric hindrance.