Structural characterisation of a series of acetylide-functionalised oligopyridines and the synthesis, characterisation and optical spectroscopy of platinum di-ynes and poly-ynes containing oligopyridyl linker groups in the backbone

A series of trimethylsilyl-protected bis(ethynyl)oligopyridine derivatives Me₃SiC≡C-R-C≡C-SiMe₃ (R = 2,2′-bipyridine-5,5′-diyl (1a), 2,2′-bipyridine-6,6′-diyl (2a), 2,2′:6′,2″-terpyridine-6,6″-diyl (3a), 4′-phenyl-2,2′:6′,2″-terpyridine-6,6″-diyl (4a)) has been synthesised and 2a-4a have been characterised by single crystal X-ray crystallography. The corresponding terminal di-ynes H-C≡C-R-C≡CH (1b-4b) and their dinuclear platinum(II) complexes trans-[(Et₃P)₂(Ph)Pt-C≡C-R-C≡C-Pt(Ph) (Et₃P)₂] (1M-4M) have been characterised spectroscopically and by single-crystal X-ray crystallography for 2M. Novel platinum(II) poly-yne polymers trans-[Pt(PBuⁿ₃)₂-C≡C-R-C≡C-] _n (1P-4P) containing the oligopyridyl linker groups in the backbone have been synthesised by the CuI-catalysed dehydrohalogenation polycondensation reaction of 1b-4b and trans-[(Bu₃P)₂PtCl₂] in Prⁱ₂NH-CH₂Cl₂. The polymeric materials exhibit decreasing thermal stability with increasing number of pyridine units in the linker group. In the absorption and phosphorescence spectra, the platinum(II) poly-yne and di-yne complexes 1P, 1M show red shifts whereas the complexes 2P-3P, 2M-3M show blue shifts of the S₁ and T₁ states. At room temperature, the phosphoresence spectra indicate some excimer formation whereas at 10 K, only intra-chain emission occurs. The results of the photophysical studies are compared with those obtained for other platinum(II)-containing poly-ynes and related organometallic polymers.