Heterospin biradicals provide insight into molecular conductance and rectification

Abstract

Properties of two isomeric triplet ground state biradical molecules, which serve as constant-bias analogs of single-molecule electronic devices, are described and experimental results are compared with transport calculations in a device geometry.

Transferrable property relationships between magnetic exchange coupling and molecular conductance

“…The synthesis and characterization of SQ-BCO-NN, SQ-Ph-NN, SQ-Th-NN, SQ-Ph 2 -NN, SQ-Py-Th-NN, and SQ-Th 2 -NN have been published previously. 1,17,20,26,35,39,41,42 See the ESI † for the preparation and characterization (spectroscopic data, X-ray crystal structure, and magnetic characterization) of the pyridyl-bridged biradical complex, SQ-Py-NN.…”

“…Transport calculations were performed using ATK 2016.0 v16.0, [44][45][46] as detailed in our earlier work. 1 The device conguration consists of the le Au electrode, the molecular bridge (scattering region), and the right Au electrode. Both the le and right gold electrodes consist of nine layers with each layer comprised of a 3 Â 3 array of Au(111) atoms, for a total of 81 gold atoms per electrode.…”

“…1A). [1][2][3][4][5][6][7][8][9][10][11][12][13][14] To account for inherent variations in molecule-electrode binding geometries, the experimental determination of conductance (g mb ) typically requires hundreds to thousands of individual conductance measurements in order to construct conductance histograms, which allow researchers to determine both conductance distributions and the most probable conductance value. 15 Since conductance calculations oen utilize a single M-B-M geometry and the molecular geometry in the actual junction is unknown, this can make direct comparisons between theory and experiment difficult to interpret.…”

“…Since the magnetic exchange interaction (J D/A ) is proportional to H D/A 2 via eqn (5), [32][33][34][35][36] we have initiated experiments designed to explore the correlation of J D/A between donoracceptor biradical centers that are spanned by molecular bridge units (D-B-A biradicals ¼ SQ-Bridge-NN; SQ ¼ S ¼ 1/2 semiquinone, and NN ¼ S ¼ 1/2 nitronylnitroxide radical, Fig. 1B and C) 1,[17][18][19][20]26,[35][36][37][38][39][40] with computed molecular conductance values, g mb . 1 An advantage to understanding the magnitude of g mb by correlating with experimental J D/A parameters is highlighted by the fact that the variable-temperature magnetic susceptibility measurements used to determine J D/A are performed on solid-state samples with known geometries that have been determined by X-ray crystallography.…”

“…1B and C) 1,[17][18][19][20]26,[35][36][37][38][39][40] with computed molecular conductance values, g mb . 1 An advantage to understanding the magnitude of g mb by correlating with experimental J D/A parameters is highlighted by the fact that the variable-temperature magnetic susceptibility measurements used to determine J D/A are performed on solid-state samples with known geometries that have been determined by X-ray crystallography. Thus, there is a single conformation present that contributes to J D/A .…”