Highly Emissive ortho-Donor-Acceptor Triarylboranes: Impact of Boryl Acceptors on Luminescence Properties

摘要

Highly emissive ortho-donor (D)-acceptor (A) triarylboranes with different boryl acceptors are proposed. 9-Boraanthryl (1), 10H-phenoxaboryl (2), and dimesitylboryl (BMes(2), 3) acceptor moieties were combined with a fixed 9,9-dimethylacridine (DMAC) donor to produce ortho-D -A compounds. X-ray diffraction and solution nuclear magnetic resonance spectroscopy analyses reveal the sterically congested and highly twisted D -A structure. Weak N center dot center dot center dot B and C-H center dot center dot center dot pi nonbonding interactions between DMAC and boryl moieties are persistently present in the solid state of cyclic boryl-containing 1 and 2, as judged from short contacts of approximately 2.80-2.84 angstrom between the N and B atoms and of approximately 2.86-3.00 angstrom between the CH3 group and the boryl plane. This feature is further supported by computational studies for intramolecular nonbonding interactions in 1 and 2. All compounds are highly emissive with photoluminescence quantum yields (PLQYs) approaching 100% and exhibit strong thermally activated delayed fluorescence in solution and in the rigid state. Notably, a decrease in PLQY with an increase in the polarity of the solvent is less sensitive for the cyclic boryl-containing 1 and 2. In particular, 1 and 2 exhibit blueshifted fluorescence with narrow bandwidths in both toluene and a PMMA film. Theoretical studies further support the twisted structure, effective HOMO-LUMO separation, and the small singlet-triplet energy splitting, with all corroborating the observed photophysical properties.