Donor columnar structure

In the case of the trinuclear [ t-N1,C2-bzimAu]3 (bzim = benzylimidazolate), in addition to the extended structures that form with other metals (see Section 6.3), it also forms supramolecular networks, acting as an electron donor with small organic acids [48]. For example, it reacts with TCNQ (tetracyanoquinodimethane) giving rise to a columnar structure in which each TCNQ molecule is sandwiched between two units of the trinuclear complex in a face-to-face manner. Thus, the repetition of this pattern leads to a stacking of the type (Au3)(Au3)( t-TCNQ)(Au3)... 

Electron donor-acceptor (EDA) stacks have been accessed by Percec et al. [90] using partially fluorinated dendrons (Fig. 14) to form LC columnar phases. The self-assembly of the dendrons is primarily driven by phase segregation of the fluorinated chains and the aromatic units. Functionalization of the dendrons at their apex with either an aromatic electroactive donor (29a) or an acceptor (29b) group yields LC columnar structures, further aided by the additional interaction between the aromatic units, which have optoelec-... 

Figure 3.32 Schematic representation of the packing behavior of acceptor polymers having different spacer lengths in a discotic columnar structure with low molar mass donors (a) spacer too short, (b) spacer of correct length, (c) spacer too long (permission being sought from [73]).

The molecular organization in thermotropic liquid-crystal line phases is associated predominantly with a rigid anisometric architecture of the constituent single molecules. The triazines 13 were the first examples of electron donors that fotm columnar phases, which give rise to the induction of smectic liquid crystalline structures through donor-acceptor interactions (Figure 11). 

As, with the exception of the mentioned oxidized compounds, the metallomacrocycles do not crystallize forming columnar quasi-one-dimensional structures, one of the prerequisites for conductivity is not met. In addition the stacking repeat distances and the donor-acceptor distances in doped compounds cannot be controlled in any way. By using oxidizing dopants other than halogens, e.g. quinones, integrated stacks can be formed leading to insulators. 

Figure 10 Top Molecular structures of electron donor molecules 26-28 and 31, and electron acceptor molecules TNF, 29 and 30. Bottom Single-crystal X-ray structure of 1 1 mixture of triphenylene derivatives with 29 (a) or 30 (b). Schematic representation of the columnar organization of 31 with TNF (c).

Figure 13. Schematic diagram of the structure of the columnar nematic phase induced hy charge transfer interactions between an electron donor, pentakisfphe-nylelhynyl)phenyialkyl ether (in hlack), and an electron acceptor, 2,4,7-trinitrofluorenone (hatched) [37-39].

Tetra(4-dodecylphenyl)-A" " -bipyran also forms a charge-transfer complex with TCNQ as well as cation-radical charge-transfer salts, the first ones of disclike shape showing columnar mesomorphic behavior over a broad temperature range [44], This shows liquid-crystalline properties, but no evaluation of the mesophase structure has been reported up to now. The TCNQ charge-transfer salt shows only a very small electric conductivity due to the complete charge transfer between donor and acceptor. 

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