Synthesis and characterisation of new acetylide-functionalised aromatic and hetero-aromatic ligands and their dinuclear platinum complexes

A new series of rigid rod protected and terminal dialkynes with extended pi-conjugation through aromatic and hetero-aromatic linker units in the backbone, 2,5-bis(trimethylsilylethynyl)-1-(2-ethylhexyloxy)-4-methoxybenzene 1a, 2,5-bis(ethynyl)-1-(2-ethylhexyloxy)-4-methoxybenzene 1b, 5,8- bis( trimethylsilylethynyl) quinoline 2a, 5,8-bis( ethynyl) quinoline 2b, 2,3-diphenyl-5,8-bis(trimethylsilylethynyl) quinoxaline 3a, 2,3-diphenyl-5,8-bis( ethynyl) quinoxaline 3b, 4,7-bis(trimethysilylethynyl)-2,1,3-benzothiadiazole 4a and 4,7-bis( ethynyl)-2,1,3-benzothiadiazole 4b, has been synthesised. Treatment of the complex trans-[Pt(Ph)(Cl)(Et3P)(2)] with half an equivalent of the diterminal alkynes 1b-4b in (Pr2NH)-Pr-i-CH2Cl2, in the presence of CuI, at room temperature, afforded the platinum(II) di-yne complexes trans-[(Et3P)(2) (Ph) Pt-C=C-R-C=C-Pt(Ph)(Et3P)(2)] [R = 1-(2-ethylhexyloxy)-4-methoxybenzene- 2,5-diyl 1c, quninoline-5,8-diyl 2c, 2,3-diphenylquinoxaline-5,8-diyl 3c, 2,1,3-benzothiadiazole- 4,7-diyl 4c] in good yields. The new acetylide-functionalised ligands and the platinum(II) sigma-acetylide complexes have been characterised by analytical and spectroscopic methods and X-ray single crystal structure determinations for 2c-4c. The absorption spectra of the complexes 2c-4c show substantial donor-acceptor interaction between the platinum(II) centres and the conjugated ligands. The photoluminescence spectra of 1c-3c show characteristic singlet (S-1) and triplet (T-1) emissions. Both the singlet and triplet emissions as well as the absorption decrease in energy with increasing electronegativity of the spacer groups along the series 1c-4c.