Verification and Temperature-Dependent Rectification by HBQ, the Smallest Unimolecular Donor-Acceptor Rectifier.

Five years ago, rectification of electrical current was found in 4'-bromo-3,4-dicyano-2',5'-dimethoxy-[1,1'-biphenyl]-2,5-dione (), a hemibiquinone (which we will call either or HBQ) that has a very small working length (1.1 nm). Monolayers of HBQ on Au were detected by "nanodozing" atomic force microscopy (AFM) and were contacted with two types of top electrodes: either cold Au or eutectic Ga-In.

Surprisingly Big Rectification Ratios for a Very Small Unimolecular Rectifier.

To shrink electrical circuits beyond the looming practical limits of Moore's "Law", it has been a common goal to create carbon-based components. Here is the first example of a new class of donor-σ-acceptor rectifiers: hemibiquinones (HBQs). HBQs possess donor and acceptor moieties that are electronically isolated by inter-ring torsion.

Crystal structure of 4'-bromo-2',5'-dimeth-oxy-2,5-dioxo-[1,1'-biphen-yl]-3,4-dicarbo-nitrile [BrHBQ(CN)2] benzene hemisolvate.

In the crystal of the title compound, C16H9BrN2O4·0.5C6H6, the mol-ecules stack in a centrosymmetric unit cell in a 2:1 stoichiometry with co-crystallized benzene solvent mol-ecules and inter-act via various weak inter-actions. This induces a geometry different from that predicted by theory, and is unique among the hemibi-quinones heretofore reported.

Crystal structure of 4'-bromo-2,5-dihy-droxy-2',5'-dimeth-oxy-[1,1'-biphen-yl]-3,4-dicarbo-nitrile.

In the crystal of the title substituted hemibi-quinone derivative, C16H11BrN2O4 or [BrHBQH2(CN)2], the substituted benzene rings are rotated about the central C-C bond, forming a dihedral angle of 53.59 (7)°. The ring systems inter-act through an intra-molecular O-H⋯Ometh-oxy hydrogen bond, which induces a geometry quite different from those in previously reported hemibi-quinone structures.

Crystal structure of 4,4'-di-bromo-2',5'-dimeth-oxy-[1,1'-biphen-yl]-2,5-dione (BrHBQBr).

In the title compound, C14H10Br2O4, the dihedral angle between the aromatic rings is 67.29 (19)°. Both meth-oxy-group C atoms lie close to the plane of their attached ring [deviations = -0.