Electrically transmissive alkyne-anchored monolayers on gold

Abstract

Well-ordered, tightly-packed (surface coverage 0.97 × 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 σ-bonds. Electrochemical measurements using [Ru(NH₃)₆]³⁺, [Fe(CN)₆]³⁻, and ferrocenylmethanol [Fe(η⁵-C₅H₄CH₂OH)(η⁵-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.