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(PBu3n)(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)(2)PtCl2] in (Pr2NH)-N-i-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 S-1 and T-1 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.