Insights into the Luminescence Thermochromism of a Triarylboron Derivative: The Role of Intramolecular Group Interaction.

The organic fluorescent probes for temperature have received increasing interest due to their extremely high spatial and temporal resolution. A few of triarylboron derivatives, as almost the only molecular probes consisting of a single luminophore, have the ability to change their luminescent color at different temperatures. The mechanism of their luminescence thermochromism is controversial. Herein, several spectral experiments, along with time-dependent density functional theory (TDDFT) and coupled-cluster (CC) calculations, are carried out to elucidate the temperature-dependent luminescence. The CC rather than the TDDFT methods give a relatively reasonable explanation for the experimental results. Consequently, the thermochromism is now considered as the result of conformational thermal equilibria that occur in both the excited and ground states. Besides, an unusual conformer with intramolecular excimer characteristic plays a crucial role in the attractive luminescence behavior.