Charles A. Panetta

TTF-NHCO2(Ce2)2 O-TCNQBr and TTF-Co2(Ch2)2 O-TCNQBR, Two Potential Molecular Rectifiers

Abstract Aviram and Ratner have proposed that a molecule D-[sgrave]-A composed of a good electron donor (D) portion like tetrathiafulvalene, a good covalent electron acceptor (A) similar to 7,7,8,8–tetracyanoquinodimethan, and an insulating bridge of sigma bonds between them, would act as a unidirectional electrical conductor, suitable for use in rectifying devices. We report here the synthesis of two monomeric examples similar to that proposed molecule.

Molecular rectification with M|(D-σ-A LB film)|M junctions

Molecular materials of the form electron donor-sigma-bridge-electron acceptor (D-σ-A) have been synthesized and incorporated into non-centrosymmetric Langmuir-Blodgett (LB) multilayer structures. Electrical characterization has been performed using a metal|(Z-type LB film)|metal (M|LB|M) junction construction. Current density-voltage data demonstrate striking rectification behaviour. Computational modelling of the electronic structure of the material has been carried out using a first principles, density functional approach. Possible conduction mechanisms are discussed with reference to the results of this modelling.

Possible rectification in Langmuir-Blodgett monolayers of organic D-σ-A molecules

Abstract Amphiphilic molecules D-σ-A (D = one-electron organic donor, σ = saturated linking bridge, A = good organic one-electron acceptor, such as TCNQ) form Pockels-Langmuir monolayers at the air-water interface, which can be transferred as Langmuir-Blodgett films onto solid substrates. Geometry-optimized MNDO calculations for some of these molecules provide the molecular size, and rough guides for the foreward and reverse rectification barriers. Fourier transform infrared spectra of monolayers by grazing-angle reflectance are reported. Crude rectification experiments gave negative results. A modified scanning tunneling microscope revealed that a single molecule of the (n-dodecyl)-aminophenyl-carbamate of 2-bromo-5-hydroxyethoxyTCNQ (BDDAP-C- BHTCNQ), transferred as part of a Langmuir-Blodgett monolayer onto a Au | Ag | mica surface, behaves as a rectifier of electrical current.

Progress towards organic single-monolayer rectifiers☆

Abstract We outline our progress towards Langmuir-Blodgett (LB) monolayers of organic molecules that rectify electrical current (first proposed in 1973 by Aviram). LB monolayers of pyrene-carbamate-bromohydroxyethoxyTCNQ and of dodecyloxyphenyl-carbamate-bromohydroxyethoxyTCNQ have been obtained, but a proper test of their rectification could not be made. Faster and more efficient routes to TCNQ-like monofunctionalized acceptors show considerable promise.

Preparative Purification of 2-(2′-Hydroxyethoxy)terephthalic Acid with Countercurrent Chromatography

Abstract 2-(2′-Hydroxyethoxy)terephthalic acid has been completely separated from its synthetic precursor, 2-hydroxyterephthalic acid using countercurrent chromatography on a preparative scale after more common separation techniques failed.

Scanning tunneling microscopy and transmission electron microscopy of Langmuir-blodgett films of three donor-sigma-acceptor molecules: BDDAP-C-HETCNQ, BDDAP-C-HPTCNQ and BDDAP-C-HBTCNQ

Abstract Langmuir-Blodgett films of three very similar molecules, BBDAP-C-HETCNQ (1), BDDAP-C-HPTCNQ (2), and BDDAP-C-HBTCNQ (3) were studied by STM and TEM. The areas per molecule and the STM resolution decrease in the order 1 to 2 to3: it seems that disorder increases, and that a trivial change in the σ bridge linking the medium electron donor BDDAP to the strong electron acceptor TCNQ in these three molecules causes major changes in the films.

Langmur-Blodgett films of potential organic rectifiers: New scanning tunneling microscopy and non-linear optics results

Abstract Our quest for the organic rectifier is reviewed. We discuss Langmuir-Blodgett (LB) films of molecules of the type D-σ-A ( D = one-electron donor, σ = carbamate, a covalent “sigma” bridge, A = one electron acceptor ) and quote preliminary results on third-order non-linear optical properties, on efforts to see electrical rectification, and on new scanning tunneling micrographs of the LB films.

Crystal structure of DMAP-C-HMTCAQ, C30H20N6O2, N,N-dimethylaminophenyl-carbamate-2′-hydroxymethyl-11,11,12,12-tetracyano-anthraquinodimethan

C30H20N6O2,Mr=496.53, triclinic, P¯1,a=8.748(4) Å,b=10.989(3) Å,c=13.541(8) Å,α=90.67(4)°,β=99.15(4)°, γ=98.62(4)°,V=1269.8 Å3,Z=2,Dc=1.30 g cm−3, λ (Mo Kα)=0.71069 Å,μ=1.02 cm−1,F(000)=516.0,T=295(3) K,R=0.127% for 1839 observed reflections, 363 parameters. The molecule has an extended, rather than a folded geometry. The HMTCAQ moiety has mm symmetry, and is shaped like a hawk about to land. The anthraquinone ring system is folded, with a dihedral angle of 37.3°; the two propanedinitrile groups have a mutual dihedral angle of 80.2°. The dihedral angle between the central ring of the TCAQ moiety and the phenyl ring is 37.2°. The phenyl rings stack over each other with a perpendicular distance of 3.36 Å. The dipole moment of the molecule is 6.254 Debyes; the crystal Madelung energy isEM=−8.989 kJ/mol; the dispersion energy isEd=−318.370 kJ/mol; the repulsion energy isEr=130.139 kJ/mol.

Langmuir-Blodgett Films of Donor-Sigma-Acceptor Molecules and Prospects for Organic Rectifiers

Our goal is to assemble and test a unimolecular rectifier of electrical current, which could be part of a very thin (5 nm thick) electronic device. This idea, originated by Aviram in 1973, depends on the asymmetry of molecules D-σ-A, where D is a good one-electron donor (but poor acceptor), A is a good one-electron acceptor (but poor donor), and σ is a covalent bridge that keeps the molecular orbitals of D separate from those of A. We have found five molecules which self-assemble as monolayers; three contain the TCNQ moiety; three contain “greasy” dodecyl groups on the donor end (which helps in monolayer formation), but one contains only hexyl groups. All of them can be transferred to a glass or Al substrate as Langmuir-Blodgett films. Recent FTIR data for a single monolayer are presented.

Langmuir-Blodgett Films of Potential Organic Rectifiers

We review here the progress made towards the goal of a truly unimolecular device, the organic rectifier. A unimolecular device, by definition, is an electronic or other device whose active principle is based on the manipulation of the molecular geometry, or the molecular conformation, of a single organic molecule or a small cluster. This goal is at the forefront of a new field of research, called “molecular electronics” (ME), which aims to fill a future need: conventional “inorganic” microelectronic devices, based on silicon, gallium arsenide or germanium, must become ever smaller because of the need for faster electronic circuits, but the fabrication difficulties will rise rapidly and, at the nanometer level, organic molecules, with the tunability of their molecular orbitals, should offer significant advantages.