Connectivity dependent thermopower of bridged biphenyl molecules in single-molecule junctions

Abstract

<p>We report measurements on gold|single-molecule|gold junctions, using a modified scanning tunneling microscope-break junction (STM-BJ) technique, of the Seebeck coefficient and electrical conductance of a series of bridged biphenyl molecules.</p>

Extended curly arrow rules to rationalise and predict structural effects on quantum interference in molecular junctions

“…Grace et al investigated more species with p-BP-X and m-BP-X cores, in this case with directly attached para-pyridyl anchors. 82 As already seen in many cases above, for p-BP-X cores little variation was observed as the bridging substituent X was varied (ECAR-1 predicts CQI in all cases), whereas the series of m-BP-X cores shown in Fig. 20b gave a broad range of conductances.…”

“…40 We note that the nature of any substituent used to satisfy the valency of the nitrogen atom is not stated by Li et al 40 If no substituent was added to the nitrogen, the molecular core is not comparable with those studied experimentally. The inconsistencies between these two computational studies 32,40 and experimental results [80][81][82] are similar to those of ECARs.…”

“…32 For m-BP-X cores, their method predicts a conductance trend of X = NH > O > SiH 2 > CH 2 , which is not consistent with the experimental observations discussed above. [80][81][82] For example, dibenzofuran tends to give low conductance and in some cases fluorene derivatives exhibit very high conductance. Li et al's "twopathway" tight-binding approach qualitatively matches the observed tendency of carbazoles (X = NR) with meta-connectivity to have higher conductance than analogous dibenzofurans (X = O) and dibenzothiophenes (X = S), although their calculations indicate that the latter pair are not significantly less conductive than the former.…”

“…Structures of further molecular wires with m-BP-X cores studied by (a) Klausen et al;81 and (b) Grace et al82 …”

Control of Intramolecular Electron Transport Pathways by Varying Localized Electron Distribution

“…27 The proton on the nitrogen atom can be removed through alkalization to create a localized electron density distribution on the carbazole center, and then recovers by acidification, 28 which acts as an ideal platform for regulating electron transport pathways through an in-situ chemical reaction. 29,30 In addition, to quench the negative charge, methyl trifluoromethanesulfonate (MeOTf) was also used to methylate the carbazole anion derivatives to confirm the formation of the localization further. 31 Compound Para-N-H and Meta-N-H were prepared through the reported procedures (more details in supporting information (SI) section 1).…”