Christian A. Christensen

Formation of oriented molecular nanowires on mica surface

Molecular “nanowire” structures composed of the charge transfer complex of a bis-tetrathiafulvalene substituted macrocycle and tetrafluorotetracyanoquinodimethane were constructed on mica substrates by employing the Langmuir–Blodgett technique. The nanowires transferred from a dilute aqueous potassium chloride subphase had typical dimensions of 2.5 nm × 50 nm × 1 μm. The nanowires are oriented to specific directions, corresponding to the directions of the potassium-ion array on the mica surface having sixfold symmetry. Such correlation between the nanowires and the substrate surface was also observed when a dilute aqueous rubidium chloride subphase was used. On the other hand, the correlation completely disappeared when the subphase contained divalent cations, indicating that the molecular nanowires orient by recognizing the monocation array on the mica surface. The nanowires formed by the vertical dipping method coexist with the monolayers. Only nanowire structures are, however, observed when we apply the horizontal lifting method. Based on the crystal structure of a related complex, a possible structure of the nanowires is presented. The conductivity of the nanowires was estimated to be of the order of 10−3 S⋅cm−1. The nanowires formed specific (regular) structures such as T-shape junctions, suggesting their use in construction of future molecular nanoscale devices.

New strategies and building blocks for functionalised 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivatives, including pyrrolo-annelated derivatives and π-extended systems with intramolecular charge-transfer

A range of new functionalised 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ) derivatives have been synthesised from the key di(halomethyl) building blocks, 10-[4,5-bis(bromomethyl)-1,3-dithiol-2-ylidene]-anthracene-9(10H)-one 10, 10-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]anthracene-9(10H)-one 11 and 9-[4,5-bis(chloromethyl)-1,3-dithiol-2-ylidene]-10-[4,5-bis(hexylsulfanyl)- 1,3-dithiol-2-ylidene]-9,10-dihydroanthracene 18. A Diels-Alder strategy comprising trapping of the transient exocyclic diene 19, which is derived from 18, with 1,4-naphthoquinone leads to the aromatised TTFAQ anthraquinone system 21. Horner-Wadsworth-Emmons olefination of 21 with the anion generated from reagent 22 gave the fused bis(TTFAQ) structure 23. Pyrrolo-annelated derivatives 30-34 have been obtained in a sequence of reactions from compound 10. Mono-formylation of the pyrrole ring of 32 and 33 under Vilsmeier conditions gave 35 and 36 which upon reaction with 2,4,5,7-tetranitrofluorene gave the donor-pi-acceptor diads 38 and 39. Cyclic voltammetry (CV) in solution for all the TTFAQ derivatives shows the typical quasi-reversible two-electron oxidation wave of the TTFAQ core at potentials which vary slightly depending on the substituents. For example, the value of Eox is raised by the electron withdrawing anthraquinone and tetranitrofluorene units of 21 and 38, respectively. The CV of the conjugated TTFAQ dimer 23 showed two, two-electron oxidation waves corresponding to the sequential formation of 23(2+) and 23(4+) (delta Eox = 130 mV) providing evidence for a significant intramolecular electronic interaction, i.e. the dication 23(2+) acts as a conjugated donor-pi-acceptor diad, thereby raising the oxidation potential of its partner TTFAQ unit. Spectroelectrochemical studies on 23 support this explanation. A strong intramolecular charge transfer band at lambda max 538 nm is seen in the UV-Vis spectra of the TTFAQ-pi-tetranitrofluorene diads 38 and 39. The X-ray crystal structures are reported for compounds 30, 33 and 34. The pyrrolo-TTFAQ moiety adopts a saddle-shape with the central ring of the dihydroanthracene moiety folded along the C(9) ... C(10) vector in each case. Significant intermolecular interactions are observed in the structures.

Synthesis and electrochemistry of a tetrathiafulvalene (TTF)21–glycol dendrimer: intradendrimer aggregation of TTF cation radicals

The convergent synthesis of a TTF–glycol dendrimer is reported: thin layer cyclic voltammetric studies on (TTF)21 system 11 show that all the TTF units undergo two single-electron oxidations to produce the 42+ redox state spectroelectrochemical studies establish that there are intradendrimer interactions between partially-oxidised TTF units.

Langmuir–Blodgett films of bis-tetrathiafulvalene substituted macrocycle and TCNQ derivatives

Tetracyanoquinodimethane (TCNQ) derivatives, 2-fluoroTCNQ (F 1 TCNQ), 2,5-difluoroTCNQ (F 2 TCNQ) and 2,5-dichloroTCNQ (Cl 2 TCNQ) were applied to form molecular nanowire structures of charge transfer complex with dialkyl derivative of bis-tetrathiafulvalene substituted macrocycle (1). When we used Cl 2 TCNQ, nanowire network structure was obtained as in the case of tetrafluoroTCNQ (F 4 TCNQ) previously reported. Although the nanowires were shorter compared with those of F 4 TCNQ complex and formed bundles, they oriented in specific directions recognizing the ionic array on mica surface. In the case of F 1 TCNQ and F 2 TCNQ, we obtained nanowire structures almost identical with those of pure 1. The Cl 2 TCNQ formed an ionic complex with 1, in which donor units and Cl 2 TCNQ were in fully charge-transferred state. Reflecting the electronic structure, the conductivity of nanowires was estimated to be 2x10 -4 S cm -1 .

Crystal structures and optical properties of cation radical salts of a tetrathiafulvalene trisannulated macrocycle

Cation radical salts of the bis(methylthio)tetrathiafulvalene (DMT-TTF) trisannulated macrocycles, [tris(DMT-TTF)]I3– (1) and [tris(DMT-TTF)]IBr2– (2), were prepared and the crystal structures and polarized reflectance spectra of the salts 1 and 2 were investigated. An isostructural character is observed for the two salts. The C3 symmetry of tris(DMT-TTF) bearing three equivalent DMT-TTF units (A, B, and C) within a molecule is broken through the formation of cation radical salts. Two DMT-TTF units (B and C) of three equivalent units form an intramolecular dimer structure through the face-to-face π–π overlap, whereas the plane of the A unit is orthogonal to the dimer plane and isolated from the other units. The intramolecular dimers are further dimerized through the intermolecular B–B′ interaction, resulting in a DMT-TTF tetramer unit (C–B–B′–C′) within the crystal. The intramolecular bond lengths and polarized reflectance spectra indicate the localization of a unit charge on the B unit rather than A or C. The charge separated A0–B+–C0 electronic structure is confirmed.

A novel hexakis(tetrathiafulvalene) derivative: synthesis, structure and electrochemical properties

The hexakis(TTF) derivative 3 has been synthesised in 89% yield by six-fold reaction of the thiolate anion of reagent 2 with hexakis(bromomethyl)benzene: the solution electrochemistry of 3 shows sequential formation of the hexa- (radical cation) and the dodecacation species, and spectroelectrochemistry shows interacting radical cations; the X-ray crystal structure of 3 is reported.

Structure and electronic properties of TTF bisannulated 24-crown-8 charge transfer complexes

Abstract Charge transfer (CT) complexes of tetrathiafulvalene bisannulated 24-crown-8 (1) with tetrafluoro (F 4 )-, 2,5-dibromo (Br 2 ), 2,5-dichloro (Cl 2 )-tetracyanoquinodimethane (TCNQ), and 2,3-dicyano-5,6-dichloro- p -benzoquinone (DDQ) were prepared. The electronic ground state of the acceptor varies from the completely ionic to partial charge transfer state. Within the CT complexes the donor 1 was completely oxidized to the divalent cationic state 1 2+ . The molecular conformation of 1 2+ in Cl 2 -TCNQ complex was an intra-dimer form folded over the flexible part of macrocyclic 24-crown-8.

The first Diels–Alder reaction of a 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivative: synthesis and crystal structure of a novel donor–π–anthraquinone diad

An exocyclic diene derivative of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene undergoes Diels–Alder reaction with naphthoquinone to provide the D–π–A diad 10.

Structural Change in Langmuir-Blodgett Films of Bis-Tetrathiafulvalene Annelated Macrocycle–Tetrafluorotetracyanoquinodimethane Charge Transfer Complex

We have already reported a nanowire structure of bis-tetrathiafulvalenb(bis-TTF)annelated macrocycle–tetrafluorotetracyanoquinodimethane(F4TCNQ)charge transfer complex formed by Langmuir-Blodgett(LB)technique. Nanowires oriented on the mica substrates forming an angle of 60 degree to each other recognizing hexagonal potassium array of mica surface. In the present study, we examined the conditions for obtaining well oriented nanowiresand found that the nanowire orientation was quite sensitive to the temperature and potassium-ion concentration of subphase as well as the deposition speeds. By a slight change in conditions, a variety of nanowire morphology was observed on mica surface.

Electrochemically controlled interactions between TTF-based dendrimers and an electron-rich oligomer

Electrochemically controlled interactions have been shown to occur between TTF containing dendrimers 1 and 2 and the electron-rich oligomer 3.