Bis(9-Boraphenanthrene) and Its Stable Biradical

Sarkar, S. K.; Hollister, K. K.; Molino, A.; Obi, A. D.; Deng, C.-L.; Tra, B. Y. E.; Stewart, B. M.; Dickie, D. A.; Wilson, D. J. D.; Gilliard Jr., R. J. Bis(9-Boraphenanthrene) and Its Stable Biradical. Journal of the American Chemical Society 2023, 145, 21475-21482.

Abstract

Selective and site-specific boron-doping of polycyclic aromatic hydrocarbon frameworks often give rise to redox and/or photophysical properties that are not easily accessible with the analogous all-carbon systems. Herein, we report ligand-mediated control of boraphenanthrene closed- and open-shell electronic states, which has led to the first structurally characterized examples of neutral bis(9-boraphenanthrene) (23) and its corresponding biradical (4). Notably, compounds 2 and 3 show intramolecular charge transfer absorption from the 9-boraphenanthrene units to p-quinodimethane, exhibiting dual (red-shifted) emission in solution due to excited state conjugation enhancement (ESCE). Moreover, while boron-centered monoradicals are ubiquitous, biradical 4 represents a rare type of open-shell singlet compound with 95% biradical character, among the highest of any reported boron-based polycyclic species with two radical sites.

Last updated on 10/04/2023