Synthesis, characterization and optoelectronic properties of dimeric and polymeric metallaynes derived from 3,6-bis(buta-1,3-diynyl)-9-butylcarbazole

A thermally stable platinum(II) polyyne polymer incorporating carbazole-based linking units, trans-[-Pt(PBu3)2C≡ CC≡CRC≡CC≡C-]n(R = 9-butylcarbazole-3,6-diyl), was prepared by polycondensation polymerization of trans-[PtCl2(PBu3)2] with H-C≡CC≡CRC≡CC≡C-H. We report the optical absorption and photoluminescence spectra of this carbon-rich metallopolymer and compare its photophysics with its molecular dinuclear model complex trans-[Pt(Ph)(PEt3)2C≡CC≡CRC≡CC≡CPt(Ph)(PEt3)2] as well as the group 11 gold(I) congener, [(PPh3)AuC≡CC≡CRC≡CC≡CAu(PPh3)]. Characterization of the polymer and metal complexes was accomplished by FT-IR and NMR spectroscopies and FAB mass spectrometry. Our investigations showed that harvesting of the organic triplet emissions can be achieved by the heavy-atom effect of Pt and Au centers, 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 C≡C chain length on the intersystem crossing rate and the spatial extent of singlet and triplet excitons is characterized. The present work indicates that high-energy triplet states intrinsically give more efficient phosphorescence in metal-containing diethynylcarbazole systems than in the corresponding bis(butadiynyl) congeners and can thus enhance the radiative decay pathway.