1 research outputs found
Deep Red Phosphorescence of Cyclometalated Iridium Complexes by <i>o</i>‑Carborane Substitution
Heteroleptic (C<sup>∧</sup>N)<sub>2</sub>IrÂ(acac) (C<sup>∧</sup>N = 5-MeCBbtp
(<b>5a</b>); 4-BuCBbtp (<b>5b</b>); 5-BuCBbtp (<b>5c</b>); 5-(<i>R</i>)ÂCBbtp = 2-(2′-benzothienyl)-5-(2-<i>R</i>-<i>ortho</i>-carboran-1-yl)-pyridinato-C<sup>2</sup>,N, R = Me and <i>n</i>-Bu; 4-BuCBbtp = 2-(2′-benzothienyl)-4-(2-<i>n</i>-Bu-<i>ortho</i>-carboran-1-yl)-pyridinato-C<sup>2</sup>,N, acac = acetylacetonate) complexes supported by <i>o</i>-carborane substituted C<sup>∧</sup>N-chelating
ligand were prepared, and the crystal structures of <b>5a</b> and <b>5b</b> were determined by X-ray diffraction. While <b>5a</b> and <b>5c</b> exhibit a deep red phosphorescence
band centered at 644 nm, which is substantially red-shifted compared
to that of unsubstituted (btp)<sub>2</sub>IrÂ(acac) (<b>6</b>) (λ<sub>em</sub> = 612 nm), <b>5b</b> is nonemissive
in THF solution at room temperature. In contrast, all complexes are
emissive at 77 K and in the solid state. Electrochemical and theoretical
studies suggest that the carborane substitution leads to the lowering
of both the HOMO and LUMO levels, but has higher impact on the LUMO
stabilization than the HOMO, resulting in the reduction of the triplet
excited state energy. In particular, the LUMO stabilization in the
4-substituted <b>5b</b> is more contributed by carborane than
that in the 5-substituted <b>5a</b>. The solution-processed
electroluminescent device incorporating <b>5a</b> as an emitter
displayed deep red phosphorescence (CIE coordinate: 0.693, 0.290)
with moderate performance (max η<sub>EQE</sub> = 3.8%) whereas
the device incorporating <b>5b</b> showed poor performance,
as well as weak luminance