Intrachain Electron and Energy Transfers in Metal Diynes and Polyynes of Group 10−11 Transition Elements Containing Various Carbazole and Fluorene Hybrids

Abstract

A series of soluble and thermally stable group 10 platinum(II) polyyne polymers of the type [−C≡C−Pt(PBu 3 ) 2 −C≡C− X −] n along with their corresponding dinuclear model compounds [Ph−Pt(PEt 3 ) 2 −C≡C] 2 − X − and [Ph 3 P−Au−C≡C] 2 − X − where X = F, Cz′, Cz, Cz − F, ( Cz ) 2, ( Cz ) 3 and Cz − F − Cz; F = 2,7-fluorene, Cz′ = 2,7-carbazole, Cz = 3,6-carbazole, were prepared and characterized. The electronic spectra (absorption, excitation, emission and ns transient absorption spectra) and the photophysical properties of these metalated compounds in 2MeTHF at 298 and 77 K are reported. These findings are correlated to the computational data obtained by density functional theory (DFT). Evidence for intramolecular singlet electron and triplet energy transfers from the Cz chromophore to the F moiety is provided and discussed in detail for those with organic spacers consisting of the carbazole−fluorene hybrids. The rate for electron transfer is very rapid ( k et > 4 × 10 11 s −1 at 298 K) whereas that for triplet−triplet energy transfer is much slower ( k ET ∼ ca. 10 3 s −1 time scale). The k ET values for the digold dyads are lower than that found for the diplatinum analogues, which are slower than the corresponding platinum-containing polymers. The observed increase in k ET for the dinuclear systems is explained by the triplet excited state population of the diplatinum species as compared to the digold congener, and for the polymers, the larger rates (twice as fast) are due to the presence of two fluorene chromophores flanking the carbazole-containing unit, hence providing two pathways to relaxation.