An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-...An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-carborane (7,8-dicarba-nido-undecaborane) cage,i.e.,at the ortho position to the cage,in the PhBMes2acceptor moiety of nido-carborane–triarylborane dyads (nido-1–4).The crystal structure of 8-H substituted nido-1 reveals the existence of steric congestion around the cage,resulting in a highly twisted connectivity between the cage plane and the Ph ring (θ=85.7°).All compounds with different 8-R groups (R=H,Me,iPr) exhibit strong TADF with long emission lifetimes (τ_(d)=4.8–9.7 μs in THF) in both THF and PMMA films,which is supported by a very small singlet–triplet energy splitting (ΔE_(ST)< 0.03 eV).Attaching an additional Me group to the ortho position of the BMes2group further enhances the intensity of delayed fluorescence (nido-4).Theoretical studies show that although nido-1–4 reach their local energy minima in a perpendicular arrangement between the cage plane and the Ph ring,there exist large energy barriers to cage rotation.In contrast,the reference compound lacking a 4-Me group,which exhibits very weak delayed fluorescence in solution,has low rotational energy barriers.展开更多
基金supported by the Basic Science Research Program funded by the Ministry of Science and ICT(NRF-2019R1A2C1084952 for M.H.Lee and NRF-2018R1A2B6006320 for S.U.Lee)through the National Research Foundation of Korea(NRF).
文摘An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-carborane (7,8-dicarba-nido-undecaborane) cage,i.e.,at the ortho position to the cage,in the PhBMes2acceptor moiety of nido-carborane–triarylborane dyads (nido-1–4).The crystal structure of 8-H substituted nido-1 reveals the existence of steric congestion around the cage,resulting in a highly twisted connectivity between the cage plane and the Ph ring (θ=85.7°).All compounds with different 8-R groups (R=H,Me,iPr) exhibit strong TADF with long emission lifetimes (τ_(d)=4.8–9.7 μs in THF) in both THF and PMMA films,which is supported by a very small singlet–triplet energy splitting (ΔE_(ST)< 0.03 eV).Attaching an additional Me group to the ortho position of the BMes2group further enhances the intensity of delayed fluorescence (nido-4).Theoretical studies show that although nido-1–4 reach their local energy minima in a perpendicular arrangement between the cage plane and the Ph ring,there exist large energy barriers to cage rotation.In contrast,the reference compound lacking a 4-Me group,which exhibits very weak delayed fluorescence in solution,has low rotational energy barriers.
