Self-assembled monolayers (SAMs) formed from Z-β-[N-(ω-acetylthioalkyl)-4-quinolinium]-α-cyano-4-styryldicyanomethanide (1) on gold-coated highly oriented pyrolytic graphite exhibit asymmetric current–voltage characteristics that are independent of the length of the linking group [Au-S-CnH2n-Q3CNQ where 3 ≤
≤ 12]. The contribution to the electrical asymmetry arising from the chromophore being asymmetrically located between the electrodes is negligible compared to that induced by the non-planar donor–(π-bridge)–acceptor moiety. Current rectification ratios of 30 at ±1 V are typical (cf. 8 for C16H33-Q3CNQ Langmuir–Blodgett films) but also fall within the range 10 to 80 at ±1 V. Molecular dimensions within the film are consistent with the D–π–A chromophores being upright and closely packed: the thickness increases with the length of the linking CnH2n group and areas of 0.33 ± 0.03 nm2 molecule−1 approximate to the van der Waals cross-section of the chromophore.
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