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Deep Red Phosphorescence of Cyclometalated Iridium Complexes by <i>o</i>-Carborane Substitution
Bae, Hye Jin,Chung, Jin,Kim, Hyungjun,Park, Jihyun,Lee, Kang Mun,Koh, Tae-Wook,Lee, Yoon Sup,Yoo, Seunghyup,Do, Youngkyu,Lee, Min Hyung American Chemical Society 2014 Inorganic chemistry Vol.53 No.1
<P>Heteroleptic (C<SUP>∧</SUP>N)<SUB>2</SUB>Ir(acac) (C<SUP>∧</SUP>N = 5-MeCBbtp (<B>5a</B>); 4-BuCBbtp (<B>5b</B>); 5-BuCBbtp (<B>5c</B>); 5-(<I>R</I>)CBbtp = 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>Ir(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.</P><P>The introduction of an <I>o</I>-carborane to the 4- or 5-position of the pyridine ring of a btp ligand in heteroleptic (C<SUP>∧</SUP>N)<SUB>2</SUB>Ir(acac) complexes leads to deep red phosphorescence, which is substantially red-shifted compared to that of (btp)<SUB>2</SUB>Ir(acac). The solution processed PhOLED devices incorporating the 5-carborane substituted Ir(III) complex as an emitter display moderate performance with deep red phosphorescence.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-1/ic401755m/production/images/medium/ic-2013-01755m_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic401755m'>ACS Electronic Supporting Info</A></P>
Chung, Woosuk,Ryu, Min Jeong,Heo, Jun Young,Lee, Soomin,Yoon, Seunghwan,Park, Haram,Park, Sangil,Kim, Yangsik,Kim, Yoon Hee,Yoon, Seok Hwa,Shin, Yong Sup,Lee, Won Hyung,Ju, Xianshu,Kweon, Gi Ryang,Ko, Lippincott Williams & Wilkins 2017 Anesthesiology Vol.126 No.2
<P>Conclusions: Sevoflurane exposure during the critical period induces mitochondrial hyperactivity and transient imbalance of excitatory/inhibitory synaptic transmission, without long-lasting behavioral consequences. Further studies are needed to confirm sexual differences and to define the role of mitochondrial activity during anesthesia-induced spine formation.</P>