Discotic lamellar

Two other di-substituted species were examined by Ohta and coworkers. The tetra alkoxyl-containing 5,15-bis(3,4-didodecyloxyphenyl)porphyrin displayed a discotic lamellar mesophase with a melting point of 60.4 °C and clearing point of 200.7 °C (Figure 23). Four crystalline phases and one undetermined mesophase were delineated for 5,15-bis(4-didodecyloxybiphenyl)porphyrin between initial crystalline phase transitions at 40.1 °C to melting to the mesomorphic material at 430.9 °C (Figure 24). The material was observed to decompose at 450.5 °C. ... 

Dithiolate compounds are similar to the carboxylates, with sulfur atoms taking the place of the oxygen atoms in the polar head. Each of the tetrakis(alkyldithiolato)dinickel(II) complexes ((101) R = C H2 +i, n = 4- ) shows a monotropic lamellar mesophase between 80and 90°C, which has been described as discotic lamellar (Dl) phase (see Figure 22). In the case where R is a branched chain, an enantiotropic Colh and a monotropic Dl mesophases have been found for tetrakis( 1 -ethylpentyldithiolato)dinickel(II) complex. ... 

Other 5,15-disubstituted porphyrins were described by Ohta and co-workers, but most do not fit the label polycatenar and are described in the section on discotic materials (Section 1.9.12). However, one derivative did possess a more conventional tetracatenar structure (131) and was reported as showing the so-called discotic lamellar phase. While it does not contain a central metal, it is included here for completeness. 

POM characterization revealed that Poly-2 has a batonnet-like texture from 125 to 94 °C and a fan-shaped texture from 94 to 80 °C during the cooling process. On the other hand, Poly-3 has a sandy texture from 142 to 112 °C and a batonnet-like texture from 112 to 93 °C during the cooling process. XRD measurements revealed that Poly-2 has a discotic nematic (No) phase at higher LC temperatures and a discotic lamellar (Dl) phase at lower LC temperatures. Poly-3 showed a Nq phase and a hexagonal columnar (CoL) phase at higher and lower LC temperatures, respectively. The phase transition temperatures of Poly-2 and Poly-3 are summarized in Table 11.2. 

Fig. 11.8 Schematic representation of LC PMPs after magnetically forced alignment. The a discotic lamellar (Dl) structure of Poly-2 and the b hexagonal columnar (Colh) structure of Poly-3 at room temperature. Reprinted with permission from [13]. Copyright 2009, Elsevier...

Shimitzu et al. [165] have reported the mesophase behaviour of 5,10,15,20-tetrakis(4-n-dodecylphenyl)porphyrin (Scheme 46) [165]. The material is easily synthesized from pyrrole and 4-n-dodecylbenzaldehyde by refluxing in propionic acid [166]. The DSC trace shows the presence of two distinct mesophases. X-ray analysis of the two mesophases indicated that their structure is very similar, and is defined as discotic lamellar (D]). 

It has been shown that a j8-diketonate liquid crystal containing palladium(II) and oxo-vanadium(IV), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), has been prepared and characterized palladium complexes are mesomorphic but their identification is difficult due to their decomposition in the isotropic phase the complex n = 10 seems to present a Nj phase on the basis of optical microscopy. The vanadium complexes are enantiotropic discotic [75], while the vanadium complex, 30, presented by Styring et al. [76] (n= 10), exhibited a short monotropic columnar discotic phase. 

---