| Summary: | Diisocyanide ligands with a <i>m</i>-terphenyl backbone provide access to Mo<sup>0</sup> complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic Ru<sup>II</sup> polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo<sup>0</sup> complexes depend strongly on whether methyl- or <i>tert</i>-butyl substituents are placed in α-position to the isocyanide groups. The bulkier <i>tert</i>-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo<sup>0</sup> center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to Ru<sup>II</sup> polypyridines, the molecular distortions in the luminescent <sup>3</sup>MLCT state relative to the electronic ground state seem to be smaller in the Mo<sup>0</sup> complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo<sup>0</sup> tris(diisocyanide) complexes than in [Ru(2,2′-bipyridine)<sub>3</sub>]<sup>2+</sup>.
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