Cross-conjugation increases the conductance of meta-connected fluorenones

Abstract

In meta-connected fluorenones, the carbonyl group almost negates the effects of destructive quantum interference, compared with corresponding meta-connected fluorenes.

Single-Molecule Junction Origami

“…[20] Similarly, we can discount an interpretation of our results based on the formation of shorter junctions through Au-carbonyl contacts, as no interactions between a (di)ketone and gold electrodes (e.g. in measurements of molecular wires containing fluorenones, [30] anthraquinones [31] or diketopyrrolopyrroles [32] ) have been reported. To verify that a syn ⇌ anti conformation change is responsible for the observed mechanoresistive effects, we performed power spectral density (PSD) analysis [33] on the junctions in their relaxed and compressed state.…”

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

“…10a). 38 As these, and species from separate studies discussed below, have cores consisting of bridged biphenyls with para-or meta-type connectivity, the molecular cores will be referred to as p-BP-X and m-BP-X, respectively, where X indicates the functionality bridging the biphenyl (BP). For either pyridyl or thiol anchoring groups, the conductance of 2,7-connected p-BP-CMe 2 and p-BP-CO was similar, as would be expected based on ECAR-1, which predicts CQI for any X unit (Fig.…”

“…With 3,6-connectivity, conductance was low in the case of m-BP-CMe 2 , but close to that of the p-BP-X series for m-BP-CO. CARs, as previously presented, would suggest poor conductance for both m-BP-X cores, and indeed the authors state "no bond-alternation path directly connects the [anchors]". 38 Based on computational studies, they conclude that "unlike a methylene carbon, the carbonyl group provides significant coupling between the two phenyl rings". 38 This is precisely the implication of ECARs, which agree with the experimental observation.…”

“…38 Based on computational studies, they conclude that "unlike a methylene carbon, the carbonyl group provides significant coupling between the two phenyl rings". 38 This is precisely the implication of ECARs, which agree with the experimental observation. The fluorenone carbonyl is an EWG which can independently accept a lone pair from a D group placed in either anchoring position (Fig.…”

“…3,5,10,29,[36][37][38][39][40][41][42] A general conclusion is that heteroatom substitution has little or no effect on CQI [39][40][41][42] but can greatly influence DQI. 10,36,38 Charge-transport simulations of molecular conductance rely on the calculation of the transmission function of a molecular junction. 1 Transmission functions can also be deter-mined experimentally.…”