Study of chemical structure and conjugation length in organometallic Pt(II) oligomers and polymers containing 1,4-diethynylbenzene derivatives as bridging units

The synthesis of platinum containing organometallic rigid rod oligomers and polymers, of general formula—[PtL2(CCpC6H4(2,5-R)2CC)]n, where L=PPh3, PBu3; R=H, OC4H9 or OC16H33, has been carried out. The multinuclear macromolecules have been prepared by the Stille coupling in the extended one pot version. Oligomers of different chain lengths were obtained and fully characterised by means of spectroscopic techniques. Different organic spacers and precursor metal complexes have been employed in order to study and compare the reaction products. Well-defined oligomers were isolated and X-ray photoelectron spectroscopy technique provided information about the chain length and the nature of the end-groups. Luminescence and absorption studies of the newly synthesised Pt based poly-ynes are also reported. A correlation between the chain length, the nature of ligand phosphines and organic spacers with the optical properties was rationalised. The Pt metal centre played an important role in the conjugation, showing a red shift of absorption maxima upon increasing the number of repeating units. Band gaps of about 2.8–3.0 eV were found, corresponding to blue-light emission with a quantum efficiency up to about 3% for measurements performed in solution.