Harvesting of organic triplet emissions in metal diynes and polyynes of group 10-12 transition elements containing the conjugation-interrupting diphenylfluorene unit

Soluble and thermally stable group 10 platinum(II) and group 12 mercury(II) polyyne polymers containing the diphenylfluorene moiety trans-[-Pt(PBu3)2C≡CRC≡C-]nand [-HgC≡CRC≡ C-]n(R = 9,9-diphenylfluorene) were prepared in good yields by polycondensation polymerization of trans[PtCl2(PBu3)2] or HgCl2with 9,9-bis(4-ethynylphenyl)fluorene. We report the optical absorption and photoluminescence spectra of these carbon-rich metal-based polymers and compare the results with their monomeric model complexes trans-[Pt(Ph)(PEt3)2C≡CRC≡CPt(Ph)(PEt3)2] and [MeHgC≡CRC≡CHgMe] as well as the group 11 gold(I) congener [(PPh3)AuC≡CRC≡CAu(PPh3)]. The regiochemical structures of the polymers were studied by NMR spectroscopy and by single-crystal X-ray analysis for the model platinum(II) compound. Our investigations indicate that harvesting of the organic triplet emissions can be achieved by the heavy-atom effect of group 10-12 transition metals (i.e., Pt, Au, Hg) which enables a very high efficiency of intersystem crossing from the S1singlet excited state to the T1triplet excited state. The influence of the metal and the fluorene ring on the intersystem crossing rate and the spatial extent of singlet and triplet excitons is characterized. These phosphorescent metal-organic materials show T1-S0gaps of 2.5 eV or above, which correspond to S1-S0gaps of 3.1 eV or higher. The present work indicates that high-energy triplet states (and concurrently high optical gaps) intrinsically lead to more efficient phosphorescence in metal-containing aryleneethynylenes and can facilitate the radiative decay pathway.