Synthesis, redox and optical properties of low-bandgap platinum(II) polyynes with 9-dicyanomethylene-substituted fluorene acceptors

In view of the strong electron-with-drawing nature of the cyano substituent, a blue donor/acceptor-type organometallic polymer (trans-[-Pt(PBu3)2-C≡C-R-C≡C-]n (R = 9-dicyanomethylenefluorene-2,7-diyl)) was prepared in good yield by CuI-catalyzed polymerization involving the dehydrohalogenating coupling of trans-[Pt(PBu3)2Cl2] and H-C≡C-R-C≡C-H. The thermal, redox and photoconducting properties of the polymer are reported. Electronic absorption studies indicate that it has a bandgap of 1.58 eV which is the lowest among any of the metal polyyne polymer reported in the literature. The derivatization of the polymer backbone with electron deficient dicyano-substituted electron acceptor in the side chain is found to be effective to tune the bandgap of this class of materials while maintaining their solubility and processability.