Electrically transmissive alkyne-anchored monolayers on gold

Well-ordered, tightly-packed (surface coverage 0.97 x 10(-9) mol cm(-2)) monolayer films of 1,4-bis((4-ethynylphenyl)ethynyl)benzene (1) on gold are prepared via a simple self-assembly process, taking advantage of the ready formation of alkynyl C-Au sigma-bonds. Electrochemical measurements using [Ru(NH3)(6)](3+), [Fe(CN)(6)](3-), and ferrocenylmethanol [Fe((5)-C5H4CH2OH)((5)-C5H5)] redox probes indicate that the alkynyl C-Au contacted monolayer of 1 presents a relatively low barrier for electron transfer. This contrasts with monolayer films on gold of other oligo(phenylene ethynylene) derivatives of comparable length and surface coverage, but with different contacting groups. Additionally, a low voltage transition (V-trans = 0.51 V) from direct tunneling (rectangular barrier) to field emission (triangular barrier) is observed. This low transition voltage points to a low tunneling barrier, which is consistent with the facile electron transport observed through the C-Au contacted self-assembled monolayer of 1.