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

Abstract

A series of trimethylsilyl-protected bis(ethynyl)oligopyridine derivatives Me3SiCC–R–CC–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–CC–R–CCH (1b–4b) and their dinuclear platinum(II) complexes trans-[(Et3P)2(Ph)Pt–CC–R–CC–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–CC–R–CC–]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.