Tailoring the Emission of Fluorinated Bipyridine-Chelated Iridium Complexes

New functionalized tris­(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)­iridium­(III) ((dfpypy)3Irs) complexes,
including small molecules and their dendrimer embedded analogoues,
were synthesized and characterized. It is demonstrated that both the fac-(dfpypy)3Ir-based polyphenylene dendrimers
and (triisopropylsilyl)­ethynyl (TIPSE)-substituted (dfpypy)3Ir complexes induce large bathochromic shifts (∼50 nm) of
emission bands compared with fac-(dfpypy)3Ir. This is due to the pronounced 3π–π*
character of emissive excited states and the extended conjugation.
A further remarkable feature is the small bathochromic shift of the
emissions of fac-tris­(2-phenylpyridine)iridium (fac-(ppy)3Ir)-based polyphenylene dendrimers
when compared to those of the iridium (Ir) complex core. Obviously,
the triplet metal-to-ligand charge transfer makes emission less sensitive
to extended conjugation than the 3π–π*
transition. This finding suggests new concepts for designing blue
phosphorescent dendrimer emitters. Both the dendrimers and the TIPSE-substituted
(dfpypy)3Ir complexes represent new green and the trimethylsilyl-functionalized
(dfpypy)3Ir new blue phosphorescent emitters. Incorporation
of TIPSE moieties into the ligands of iridium complex gives rise to
enhanced phosphorescence.