Electron acceptor molecules, columnar

The resulting mixtures revealed the existence of columnar mesophases, with a pronounced intracolumnar order, the stacking periodicity being in the range from 3.40 to 3.45 A. The same type of ordered columnar mesophase has been induced by mixing discotic nematic compounds with TNF. In this case, the interactions between the disks are too small in themselves to favour a columnar mesophase, but the incorporation of electron acceptor molecules such as TNF contributes to enhance the intermolecular interactions and to generate an ordered columnar mesophase. The stabilization of the columnar structure in these binary systems has been found for other types of molecules... 

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).

Induction of chirality in No phases was also shown to be possible using charge transfer interactions, via jt-jt stacking. The binary mixture of mesogen 8, which is electron rich, with chiral electron-deficient molecule 9 was shown to induce a twist in the mesophase.15 Furthermore, nonmesogenic 8 gave rise to a cholesteric mesophase, denoted as being of the columnar type (N ), when present in a ternary system with TNF (trinitrofluorenone, an electron acceptor)... 

The induction of various columnar mesophases can be realized through the doping of low molecular weight electron rich molecules with electron acceptors as schematically represented in Fig. 26. 

TABLE 4 Transition temperatures ( C, DSC data) of intermolecular donor-acceptor complexes formed spontaneously when heating equimolar mixtures of electron donor molecules (e.g. radial pentaynes of type 3b, R = H, not liquid crystalline, or the 2,3,6,7,10,11-triphenylene hexaether 4) and the non-liquid crystalline multi(nitro)fluorenone derivatives 5a, 5b or 5c as electron acceptors yielding preferably by induction the nematic or chiral nematic columnar (Ncoi or N coh respectively) phases. 

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). 

---