Photophysical Enhancement of Triplet Emitters by Coordination-Driven Self-Assembly

The quantum yields of organic fluorophores used as donors in coordination-driven self-assembly often suffer from the heavy atom effect of nearby metal sites. Here, the role of intersystem crossing from a deactivating process to one that delivers emissive triplet states was reversed. A phosphorescent trans bis-N-heterocyclic carbene platinum(II) compound, Pt(dhim)(2)(CC-4-py)(2) (D1; dhim=1,3-dihexyl-2-H-imidazol-2-ylidene), was used along with other linear donors 4,4-bipyridine (D2) and 1,4-bis(4-pyridyl ethynyl)benzene (D3) in self-assembly reactions with Pt(dtbpy)X-2 acceptors (dtbpy=4,4-di-tert-butyl-2,2-bipyridine) to afford three metallacycles. Photophysical investigations revealed that, although the building blocks used to construct M1 have relatively low quantum yields (phi=1.2 and <1% for D1 and 2, respectively), the metallacycle has a quantum yield of 14%. This increase reflects a change in radiative rate constant from 3.6x10(4)s(-1) for D1 to 2.1x10(5)s(-1) for M1.