Exploring 9-arylcarbazole moiety as the building block for the synthesis of photoluminescent group 10-12 heavy metal diynes and polyynes with high-energy triplet states

A new series of organic-soluble and thermally stable group 10 platinum(II) polyyne polymers functionalized with 9-arylcarbazole moiety trans-[-Pt(PBu ₃)₂C≡CRC≡C-]_n (R = 9-arylcarbazole-3,6-diyl; aryl = phenyl, p-methylphenyl, p-fluorophenyl) were prepared in good yields by Hagihara's dehydrohalogenative polymerization of trans-[PtCl₂(PBu₃)₂] with HC≡CRC≡CH under ambient conditions. The regiochemical structures of the polymers were characterized by multinuclear NMR spectroscopy. We discuss the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic molecular model complexes trans-[-Pt(Ph)(PEt₃) ₂C≡CRC≡CPt(Ph)(PEt₃)₂ as well as its group 11 gold(I) and group 12 mercury(II) congeners [(PPh ₃)AuC≡CRC≡CAu(PPh₃)] and [MeHgC≡ CRC≡CHgMe]. The structural properties of several model complexes were studied by X-ray crystallography. The influence of the heavy metal atom and the 9-aryl substituent of carbazole on the phosphorescence behavior and the spatial distribution of the lowest singlet (S₁) and triplet (T₁) excitons in these metalated alkynyl systems are comprehensively elucidated. The present work indicates that the efficiency of organic triplet emissions harnessed through the heavy-atom effect of group 10-12 transition metals in the main chain generally follows the order Pt > Au > Hg but the optical properties of the materials are relatively insensitive to the nature of the 9-aryl group on the carbazolyl ring. All of these metallaynyl-carbazole materials with high-energy T₁ states of 2.68 eV or higher show high phosphorescence efficiencies at low temperatures.