Herringbone packing

LB films of 1,4,8,11,15,18-hexaoctyl-22,25-bis-(carboxypropyl)-phthalocyanine (2), an asymmetrically substituted phthalocyanine, were stable monolayers formed at the water—air interface that could be transferred onto hydrophilic siUca substrates (32—34). When a monolayer film of the phthalocyanine derivative was heated, there was a remarkable change in the optical spectmm. This, by comparison to the spectmm of the bulk material, indicated a phase transition from the low temperature herringbone packing, to a high temperature hexagonal packing. 

Figure 14-16. Low temperature (LT) and high temperature (IHT) polymorphs ol qualenhiophcnc. Top view along the unique b axis botiom view along the molecular axis (note the herringbone packing) (Adapted from Refs. 791 and 82 ).

Figure 8. The 2D herringbone packing motif in (a) naphthalene, (b) biphenyl, and (c) anthracene as viewed normal to the ab plane, (d) Anticipated 1 3 pillar (black)-guest (grey) herringbone packing within the gallery regions of a templated...

Explain the fact that benzene adopts a herringbone packing motif (Figure 1.20), whereas higher aromatic hydrocarbons possess y-type or graphitic interactions. 

Fig. 14.29 5-Methyltetracene (38) and 5-bromotetracene (39), exhibiting sandwich herringbone packing.

The most dramatic example of the use of functionalization to tune the properties of an organic semiconductor is found in perfluoropentacene 41 (Scheme 3.9) [53]. Perfluoropentacene has a strongly shifted LUMO, evidenced by lowering of the reduction potential by more than 700 mV. The fluorinated compound adopts a herringbone packing in the crystal that is very similar to that of the parent acene. Top-contact FET devices made from evaporated 41 had an electron mobility of 0.11 cm2 V-1 s 1, demonstrating the change from p-type to n-type behavior. 

In addition to the hydrogen-bonding interaction, there is an important interaction in the less soluble diastereomeric salt, namely a CH tt interaction32 between the aromatic groups, which results in the formation of stable herringbone packing.33,34 This interaction works between the supramolecular columns to stabilize the assembly of the columns to build up a three-dimensional crystal (Figure 4.18). 

Cohesive Energies. The bulk phases of the nA, nP, and nT series are characterized by the so-called herringbone packing where two inequivalent molecules in the ab plane form layers perpendicular to the crystallographic c direction. At room temperature and ambient pressure the space group of the considered molecular crystals is monoclinic, except for tetracene (4A) and pentacene (5A) which crystallize in a triclinic space group. 

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