Mesomorphic Hexabenzocoronenes Bearing Perfluorinated Chains

Abstract

IntroductionExtended polyaromatic hydrocarbons (PAH) are finding increasing interest among other self-assembled supramolecular systems due to their pronounced tendency for formation of extended π-stacked assemblies. These have many potential properties, such as a high electron density which allows their use in promising applications in molecular electronics. 1 However, the main drawback of these rigid polycondensed molecules resides in the difficulty of their synthesis and their very low solubility which prevents their isolation and manipulation. Recently, Müllen and co-workers 2 succeeded in finding a versatile synthesis of hexa-perihexabenzocoronene (HBC), a polycondensed hexagonal molecule containing 13 benzene rings which shows a very high chemical stability 3 and which self-organizes into columnar stacks, by π-stacking, with an outstanding degree of order in the solid state. 4,5 Additionally, its solubility was improved by the addition of peripheral long aliphatic chains which at the same time bestows the molecule with a ditopic property: These HBC derivatives show a liquid crystalline (LC) state over a wide temperature range depending on the length of the aliphatic chain. 6 Moreover, these HBC derivatives exhibit the highest charge carrier mobility recorded so far for an organic molecule both in the solid and in the liquid crystalline states, 7 paving the way toward their application in the domain of electronic 8 and optoelectronic 9-11 devices.Nevertheless, the lateral interaction between the adjacent HBC stacks caused by the crystalline packing of their aliphatic side chains 12 constitutes a major drawback since it interferes with the formation of very long conducting π-stacks. Additionally, most of the HBCs bearing aliphatic chains are liquid crystalline just above room temperature, which leads to a second disadvantage since it induces a drastic decrease of their charge carrier mobilities, 13 which is reported to be due to "lateral" conduction and as a reason for the perturbation or the deterioration of an ideal liquid crystalline mesophase that dominates the conduction process. 14 * To whom correspondence should be addressed. Tel. (Office): +41 (0) Synthesis and characterization of new hexabenzocoronene (HBC) derivatives bearing perfluoroalkylated chains are described. These disc-shaped polycondensed aromatic hydrocarbons are known to self-assemble by π-stacking into columnar architectures. The peripheral decoration with perfluorinated chains, well-known for their low van der Waals forces, leads as expected to reduced intercolumnar interactions. Powder X-ray diffraction and differential scanning calorimetry of these perfluoroalkylated HBCs proved liquid crystalline (LC) properties whose transition temperatures, mesophase stability, and nature depend on the detailed structure of these side chains, i.e., the ratio between aliphatic and perfluorinated parts. On the other hand, the insertion of a phenyl spacer between the aromatic core and the lateral chains increases the LC transition temperature and, sur...

Discotic Liquid‐Crystalline Materials Based on Porphycenes: A Mesogenic Metalloporphycene–Tetracyanoquinodimethane (TCNQ) Adduct

“…Phases of this kind (discotic lamellar) have been documented for other discotic systems. [48] The XRD pattern recorded for 1 b at 80 8C (Figure 1) is indicative of the formation of a lamello-columnar mesophase (L Col ), similar to those observed recently for lath-like perylene diimides [49] and for disc-lath mixtures of phthalocyanines and perylenes. [50] Three sharp reflections, with reciprocal spacings in the ratio 1:2:3, are observed in the small-angle region at 34.8, 17.5, and 11.55 , respectively.…”

Diskotische Flüssigkristalle: Von der maßgeschneiderten Synthese zur Kunststoffelektronik

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Mesomorphic phase transition behavior of novel triphenylene compounds possessing fluoroalkylated side chains

“…On the other hand, several reports were also published on columnar liquid crystals possessing fluoroalkyl side chains [29][30][31][32][33][34][35][36][37][38][39][40]. For example, it was reported that all tapered building blocks, and the self-assembly polymers (perfluorinated methylenic groups of their alkyl tails) into tubular supermolecular architectures show an enantiotropic hexagonal columnar mesophase.…”