6,6'-Biindeno[1,2- b ]anthracene: An Open-Shell Biaryl with High Diradical Character.

We report in situ generation of a 6,6'-biindeno[1,2- b ]anthracene (BIA) derivative as an open-shell biaryl with high diradical character, which could be identified by mass spectrometry, NMR spectroscopy, single-crystal X-ray analysis, UV-vis-NIR absorption spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. Theoretical calculations by various methods and variable-temperature EPR analyses were performed to tackle the elusive ground state of BIA diradical, suggesting a singlet ground state with a nearly degenerate triplet state. These results provide insight into the design of unique open-shell biaryls.