Induction of Lamellar Mesomorphic Structures in Columnar-Phase-Forming 1,3,5-Triazines through Charge-Transfer Interactions with Electron Acceptors
✍ Scribed by Daniela Goldmann; Dietmar Janietz; Claudia Schmidt; Joachim H. Wendorff
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 233 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0044-8249
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✦ Synopsis
The molecular organization in thermotropic liquid-crystalline phases is predominantly associated with a rigid anisometric architecture of the constituent single molecules. Molecular self-organization may, however, also be effected by strong intermolecular forces between nonmesogenic molecules to give noncovalently bonded anisometric aggregates. The two principles can be combined by incorporating an intramolecular functionality into molecules with an anisometric shape. [1] This combination allows the control and manipulation of the structure formed by mesogens through directed intermolecular interactions with a second complementary component. Specific manipulations of columnar mesomorphic structures, for example, may arise from formation of donor ± acceptor complexes [2] or from intermolecular hydrogen bonding [3] between two different individual molecules.
ªOpen-sidedº core systems that have the capacity to form columnar phases of single components and also allow the docking of a second component to a molecular recognition site located in the inner core region (side-by-side interactions) are conceivable. Structure formation should then be possible for the same molecule through associations with electrondeficient counterparts through charge-transfer (CT) interactions perpendicular to the molecular periphery (face-to-face interactions) provided that the central part of the molecule coincidentally represents an electron donor (Figure 1). To realize this concept we have synthesized 2,4,6-triarylamino-1,3,5-triazines with long peripheral alkoxy groups and with an electron-rich polar group in the center. [7] The triazines substituted with six lipophilic side chains exhibit columnar mesophases in their pure state. [8] Furthermore, hydrogen bonding with complementary alkoxy-substituted benzoic acids gives rise to the control of the two-dimensional lattice symmetries [1, 9] and even induction of a hexagonal columnar mesophase. [10] We report here mesomorphic assemblies of the hexagonal columnar (Col hd ) phase from sixfold alkoxy-substituted 2,4,6triarylamino-1,3,5-triazines 1 a, b, [8] which act as electron evaporated (Figure 2 a). Atomic force microscopy (AFM) measurements showed that the majority of the sample consisted of a regular island structure of microcrystals, with an average size of about 10 nm, each containing approximately 2.5 Â 10 3 catalyst molecules. From the island density of about 4 Â 10 10 islands per cm 2 , a coverage of 10 14 molecules per cm 2 was estimated; this was supported by X-ray photoelectron spectroscopy (XPS) results (10 14 Pd atoms per cm 2 ). The microcrystal size implies that roughly 35 % of the catalyst molecules were located at the surface of the crystals.