Synthesis, characterisation and optical spectroscopy of platinum(ii) di-ynes and poly-ynes incorporating condensed aromatic spacers in the backbone

A series of protected and terminal dialkynes with extended π-conjugation through a condensed aromatic linker unit in the backbone, 1,4-bis(trimethylsilylethynyl)naphthalene, 2a, 1,4-bis(ethynyl)naphthalene, 2b, 9,10-bis(trimethylsilylethynyl)anthracene 3a, 9,10-bis(ethynyl)anthracene 3b, have been synthesized and characterized spectroscopically. The solid-state structures of 2a and 3a have been confirmed by single crystal X-ray diffraction studies. Reaction of two equivalents of the complex trans-[Ph(Et₃P)₂PtCl] with an equivalent of the terminal dialkynes 1,4-bis(ethynyl)benzene 1b and 2b–3b, in ⁱPr₂NH–CH₂Cl₂, in the presence of CuI, at room temperature, afforded the platinum(ii) di-ynes trans-[Ph(Et₃P)₂Pt–C≡C–R–C≡C–Pt(PEt₃)₂Ph] (R = benzene-1,4-diyl 1c; naphthalene-1,4-diyl 2c and anthracene-9,10-diyl 3c) while reactions between equimolar quantities of trans-[(ⁿBu₃P)₂PtCl₂] and 2b–3b under similar conditions readily afforded the platinum(ii) poly-ynes trans-[–(ⁿBu₃P)₂Pt–C≡C–R–C≡C–]_n(R = naphthalene-1,4-diyl 2d and anthracene-9,10-diyl 3d). The Pt(ii) diynes and poly-ynes have been characterized by analytical and spectroscopic methods, and the single crystal X-ray structures of 1c and 2c have been determined. These structures confirm the trans-square planar geometry at the platinum centres and the linear nature of the molecules. The di-ynes and poly-ynes are soluble in organic solvents and readily cast into thin films. Optical spectroscopic measurements reveal that the electron-rich naphthalene and anthracene spacers create strong donor–acceptor interactions between the Pt(ii) centres and conjugated ligands along the rigid backbone of the organometallic polymers. Thermogravimetry shows that the di-ynes possess a somewhat higher thermal stability than the corresponding poly-ynes. Both the Pt(ii) di-ynes and the poly-ynes exhibit increasing thermal stability along the series of spacers from phenylene through naphthalene to anthracene.