TCNQ-TTF system

Biopolymers, like nucleic acids (DNA and RNA), proteins, polysaccharides, lipids, and so on. have fundamental significance in life processes. Since the mid-1980s, highly conducting polymers, like doped different polyacetylenes (1) and (2) (SN) (3), or the TCNQ-TTF system (4) and (5), with quasi-one-dimensional alternating stacks of the two different types of molecule embedded in a three-dimensional molecular crystal, and PPV (6), have become objects of extensive experimental investigations because they are also candidates for the discovery of new physical phenomena, such as solitons, polarons and bipolarons, and superconductivity with higher transition temperatures (T ). 

This model, which is sometimes referred to as the Fluctuating Gap Model (FGM) [42], has been used to study various aspects of quasi-one-dimensional systems. Examples arc the thermodynamic properties of quasi-one-dimensional organic compounds (NMP-TCNQ, TTF-TCNQ) [271, the effect of disorder on the Peierls transition [43, 44, and the effect of quantum lattice fluctuations on the optical spectrum of Peierls materials [41, 45, 46]. 

Fig. 4 Electronic coupling (eV) between HOMO-Ittf and LUMOtcnq for th cofacial TTF/TCNQ model system (with an intermolecular distance of 3.45 A), as calculated with various functionals and plotted as a function of % HF exchange. This figure is adapted from [9]...

The highly conductive class of soHds based on TTF—TCNQ have less than complete charge transfer (- 0.6 electrons/unit for TTF—TCNQ) and display metallic behavior above a certain temperature. However, these soHds undergo a metal-to-insulator transition and behave as organic semiconductors at lower temperatures. The change from a metallic to semiconducting state in these chain-like one-dimensional (ID) systems is a result of a Peieds instabihty. Although for tme one-dimensional systems this transition should take place at 0 Kelvin, interchain interactions lead to effective non-ID behavior and inhibit the onset of the transition (6). 

The temperature of the metal-to-insulator transition in TTF—TCNQ is 53 K. For systems with increased interchain coupling, the transition temperature for the onset of metallic conduction increases roughly as the square of the interaction between the chains. This behavior is tme as long as the coupling between chains remains relatively weak. For compounds with strong interactions between stacks, the material loses its quasi-ID behavior. Thus, the Peieds distortion does not occur even at low temperatures, and the materials remain conductive. 

The organic conductor properties of tetrathiaflulvalenetetracyanoquino-dimethane (TTF-TCNQ) as a material for constructing electrodes, viz. its catalytic response and resistance to passivation, are of special interest for the determination of biological compounds, which usually have slow electrode kinetics and a low sensitivity, and tend to foul electrode surfaces. The response of a TTF-TCNQ microarray sensor inserted in a flow system for... 

The real-space characterization of the CDW-induced modulation of a 2D surface lattice can be ideally performed with variable temperature STMs. The temperature-dependent modulation can be classified according to the HFW model introduced in Section 4.2 taking the ideal 1x1 surface structure as the reference lattice (as and bs) and the projected CDW-modified structure as the overlayer system (uo and bo). In the case of TTF-TCNQ = a and h = b and for the images taken at 63 K... 

A metallic band structure is realized when the CT solids have a partial CT state and molecules form uniform segregated columns or layers. Figure 1 shows electrical conductivity data for 1 1 low-dimensional TTF TCNQ system, as a function of redox potentials [82]. The two lines a and b are related to the equation expressing the relationship between 7d, Ea, and the Madelung energy M 5) (5 = degree of CT) between partially charged component molecules (eq. 2) [83], where and Ea are... 

There are several interesting families of inorganic mixed-valence compounds that we have not discussed here (see Yvon, 1979 McCarley, 1982). For example, there are metal-cluster compounds such as the Chevrel phases, M,jMo6X8(X = S or Se) and condensed metal-cluster chain compounds such as TlMojScj, TijTe, NaMo O and M PtjO. TTF halides and TTF-TCNQ complexes (Section 1.9) constitute molecular mixed-valent systems in which the mixed valency is associated with an entire molecule the charge on TTF in such compounds is nonintegral. The structure of TTF-Br(, 79 and... 

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