Functionalized 8 nm Long Aryleneethynylene Molecular Wire with Alkyne Termini



The synthesis of new conjugated aryleneethynylene derivatives of up to ca. 8 nm molecular length (compound 16) with terminal alkyne substituents and 9,9-dihexylfluorene units in the backbone is described. Key synthetic steps are Pd-mediated Sonogashira coupling methodology combined with regioselective removal from the terminal alkyne units of 2-hydroxy-2-propyl protecting groups in the presence of trimethylsilyl groups. The structural and electronic properties of 16 were obtained from DFT calculations: the intramolecular terminal C···C′ distance in its relaxed conformation was found to be 7.8 nm. The calculated distribution of HOMO and LUMO orbitals and the strong blue fluorescence observed for 16 (λmax = 420, 443 nm in CHCl3 solution) are consistent with a highly conjugated penta[(9,9-dihexyl-2,7-fluorenylene)ethynylene] structure. Molecule 16 possesses multifunctionality and is of interest for future molecular electronic device applications.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)