Organic charge-transfer compounds

Koshihara S, Tokura Y, Iwasa Y, Koda T, Saito G, Mitani T (1991) Domain-wall excitation in organic charge transfer compounds investigated by photo-reflectance spectroscopy. Synth... 

Face-to-face aromatic stacking interactions are common in a wide range of organic charge-transfer compounds where there is a donor-acceptor interaction between an electron rich Ji-system and an electron... 

Staab HA (1989) New aspects of organic charge-transfer compounds syntheses, structures and solid-state properties. In Yoshida Z, Shiba T, Oshiro Y (eds) New aspects of organic chemistry I. VCH, Weinheim, pp 227-236... 

First, practically nothing is said of the tremendous development in the so called HTCS, the new oxide superconductors. It could be argued that their metallic conductivity has been known much earlier than that of organic compounds. It is indeed a field by itself, which cannot possibly be dealt with here. It is, in a way, a great pity, as many similarities are observed, for instance between the oxide compounds and the organic charge transfer compounds, as stresses above normal , superconductive or antiferromagnetic properties, quasi low dimensionality, with exacerbated electron-electron interactions when localisation into Id is approached. .. 

Charge-Transfer Compounds. Similat to iodine and chlorine, bromine can form charge-transfer complexes with organic molecules that can serve as Lewis bases. The frequency of the iatense uv charge-transfer adsorption band is dependent on the ionization potential of the donor solvent molecule. Electronic charge can be transferred from a TT-electron system as ia the case of aromatic compounds or from lone-pairs of electrons as ia ethers and amines. 

Much work has been undertaken to modify electrode surfaces with films which are themselves conducting. The most promising approaches involve organic charge transfer and radical ion polymers. Coordination chemistry has, to date, played little part in this work (a good recent review is available),67 but one example relating to ferrocene chemistry can be quoted. In this example a well known electron acceptor, 7,7, 8,8 -tetracyanoquinodimethane (TCNQ 27), is modified and incorporated into polymer (28) in which the iron(II) of the ferrocene unit is the electron donor. The electrical conductivity of such a film will depend on partial electron transfer between ion and TCNQ centres as well as on the stacking of the polymer chains. The chemistry of other materials, based on coordination compounds, which have enhanced electrical conductivity is covered in Chapter 61. 

This chapter deals with 1,3-dithiole compounds such as 1,3-dithiolylium ions (1), mesoionic l,3-dithiol-4-ones (2), 1,3-dithioles (3), 1,3-dithiolanes (4) and the tetrathiaful-valene system (5). During the last 15 years the chemistry of 1,3-dithiole compounds has developed considerably. One reason is that tetrathiafulvalene and its derivatives serve as donors in organic charge-transfer salts which exhibit the electrical properties of quasi-one-dimensional metals. For the preparation of such organic metals, 1,3-dithiolylium cations serve as useful synthetic intermediates. 

Besides the organic metals and superconductors based on the donor molecule ET numerous metallic organic charge transfer salts composed of different donors and acceptors have been synthesized. However, only a small number of these salts become superconducting, usually at rather low temperatures, and even less have been investigated in the same detail as the ET compounds. Apparently, the generally low crystal quality of the non-ET materials permitted only a few Fermi surface studies by SdH or dHvA experiments. 

Takahashi, Y. et al.. Tuning of electron injections for -type organic transistor based on charge-transfer compounds, App/. Phys. Lett., 86, 063504, 2005. 

Organic r-donors based on tetrathiafulvalene (TTF) and its derivatives have been the subject of numerous studies in organic media, due to their ability to form charge-transfer compounds and their wide range of potential applicability as, for instance, molecular conductors, semiconducting films, electroactive polymers (including low-band gap materials), molecular switches, and superconductors [8]. 

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