Synthesis, Characterization and Photoluminescence of Dimeric and Polymeric Metallaynes of Group 10–12 Metals Containing Conjugation-breaking Diphenylmethane Unit

A novel approach based on conjugation interruption was developed for a luminescent and thermally stable platinum(II) polyyne polymer trans-[–Pt(PBu3)2C≡C(C6H4)CH2(C6H4)C≡C–]n (1) containing the diphenylmethane chromophoric spacer. Particular attention was focused on the photophysical properties of this group 10 polymetallayne and comparison was made to its binuclear model complex trans-[Pt(Ph)(PEt3)2C≡C(C6H4)CH2(C6H4)C≡CPt(Ph)(PEt3)2] (2) and their closest group 11 gold(I) and group 12 mercury(II) neighbors, [MC≡C(C6H4)CH2(C6H4)C≡CM] (M = Au(PPh3) (3), HgMe (4)). The regiochemical structures of these angular-shaped compounds were studied by various spectroscopic analyses. Upon photoexcitation, each of them emits an intense purple-blue fluorescence emission in the near UV region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions harnessed through the strong heavy-atom effects of group 10–12 transition metals was examined. These metal-containing phenyleneethynylenes spaced by the conjugation-breaking CH2 unit were found to have high optical gaps and high-energy triplet states. The influence of metal and sp3-hybridized methylene conjugation-interrupters on the intersystem crossing rate and the spatial extent of the lowest singlet and triplet excitons was fully elucidated. Our investigations indicate that high-energy triplet states in these materials intrinsically give rise to very efficient phosphorescence with fast radiative decays.