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Whilst 2‐ or 5‐OMe groups on the bridging phenylene ring in [{Cp*(dppe)RuC≡C}2(μ‐1,3‐C6H4)]+ have little influence on the electronic structure of this weakly coupled mixed‐valence complex, a 4‐OMe substituent enhances ground state electron delocalization, and increases the intensity of the IVCT transition. Vibrational frequency and TDDFT calculations (LH20t‐D3(BJ), def2‐SVP, COSMO (CH2Cl2)) on ([{Cp*(dppe)RuC≡C}2(μ‐1,3‐C6H3‐n‐OMe)]+ (n=2, 4, 5) models are in excellent agreement with the experimental results. The stronger ground state coupling is attributed to the change in composition of the β‐HOSO brought about by the 4‐OMe group, which is ortho or para to each of the metal fragments. The intensity of the IVCT transition increases with the greater overlap of the β‐HOSO and β‐LUSO, whilst the relative phases of the β‐HOSO and β‐LUSO in the 4‐OMe substituted complex are consistent with predictions of constructive quantum interference from molecular circuit rules. [ABSTRACT FROM AUTHOR]

A convenient two-step, one-pot synthesis of oligo(arylene–ethynylene) (OAE) type molecular wires in yields of up to 70% via in situ desilylation of protected bis(alkynes) Me3SiC≡CArC≡CSiMe3 (Ar = 2,5-thienyl, 1,4-naphthylene, 9,10-anthrylene) and subsequent Sonogashira cross-coupling with S -(4-iodophenyl) ethanethiolate, 4-iodothioanisole, or 5-bromo-3,3-dimethyl-2,3-dihydrobenzo[ b ]thiophene is described. The in situ desilylation avoids the manipulation of the sensitive terminal dialkynes (HC≡CArC≡CH), whilst the general approach presented has some advantages over alternative synthetic strategies based on coupling of aryl dihalides (XArX) by avoiding the multi-step preparation and purification of the terminal alkynes S -(4-ethynylphenyl) ethanethiolate, 4-ethynylthioanisole and 5-ethynyl 3,3-dimethyl-2,3-dihydrobenzo[ b ]thiophene. The molecular conductance of the resulting thiolate or thioether functionalised OAE molecular wires has been determined using scanning tunneling microscope break junction (STM-BJ) methods. The trends in molecular conductance do not track simply with the degree of aromaticity of the molecular core despite the rather similar molecular lengths. Rather, the STM-BJ data are better correlated with the nature of the anchor group, highlighting the important role of electrode–molecule coupling on electron transport in a molecular junction. The experimental conductance data are in good agreement with recently described quantum circuit rules, further highlighting the potential for these relationships to be used as predictive tools in molecular electronics research. A two-step, one-pot synthesis of oligo(arylene–ethynylene) molecular wires that avoids manipulation of sensitive terminal bis(alkynes) is described. Trends in molecular conductance do not track with the molecular core aromaticity, but correlate with the recently described quantum circuit rules and associated bridge and anchor parameters. [ABSTRACT FROM AUTHOR]

A series of diarylacetylene (tolane) derivatives functionalised at the 4- and 4'-positions by thiolate, thioether, or amine groups capable of serving as anchor groups to secure the molecules within a molecular junction have been prepared and characterised. The series of compounds have a general form X-B-X, Y-B-Y, and X-B-Y where X and Y represent anchor groups and B the molecular bridge. The single-molecule conductance values determined by the scanning tunnelling microscope break-junction method are found to be in excellent agreement with the predictions made on the basis of a recently proposed 'molecular circuit law', which states 'the conductance GXBX of an asymmetric molecule X-B-Y is the geometric mean šGXBXGYBY of the conductance of the two symmetric molecules derived from it, GXBX and GYBY.' The experimental verification of the circuit law, which holds for systems in which the constituent moieties X, B, and Y are weakly coupled and whose conductance takes place via off-resonance tunnelling, gives further confidence in the use of this relationship in the design of future compounds for use in molecular electronics research. [ABSTRACT FROM AUTHOR]