Microwave-Assisted Method for the Synthesis of Perylene Ester Imides as a Gateway Toward Unsymmetrical Perylene Bisimides

A high yielding microwave-assisted synthetic method to obtain unsymmetrical perylene diester monoimide (PEI) by treating the perylene tetrester (PTE) with a requisite amine is reported. Perylene-based molecules are widely used in the construction of self-assembled supramolecular structures because of their propensity to aggregate under various conditions. In comparison to perylene bisimides (PBIs), PEIs are less studied in organic electronics/self-assembly due to the synthetic difficulty and low yields in their preparation. PEIs are less electron deficient and have an unsymmetric structure in comparison to PBIs. Further, the PEIs have a higher solubility than PBIs. The present method is applicable with a wide range of substrates like aliphatic, aromatic, benzyl amines, PTEs, and <i>bay</i>-annulated PTEs. This method provides a tuning handle for the optical/electronic properties of perylene derivatives and also provides an easy access to unsymmetrical PBIs from the PEIs

Self-Assembly of Hekates-Tris(<i>N</i>‑salicylideneaniline)s into Columnar Structures: Synthesis and Characterization

Two series of new, photoluminescent star-shaped discotic liquid crystals, recently termed as “hekates”, derived from tris­(<i>N</i>-salicylideneaniline)­s (TSANs), were synthesized by the facile threefold condensation of 3,4-bis­(alkoxy)­phenyl 4-aminobenzoates/3,4,5-tris­(alkoxy) phenyl 4-aminobenzoates with 1,3,5-triformylphloroglucinol and characterized. These two series of discotics with six and nine peripheral <i>n</i>-alkoxy tails were especially designed and accomplished to understand the relation between mesomorphic/photophysical properties and molecular structure. Proton NMR spectral analysis revealed their existence as an inseparable mixture of two keto-enamine tautomeric forms featuring <i>C</i>_3h and <i>C</i>_s rotational symmetries. A systematic study into the thermotropic liquid crystal behavior using polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering confirmed the presence of columnar (Col) phase in vast majority of the TSANs prepared. The two-dimensional (2D) lattices of these fluid columnar phases were found to be characteristic of hexagonal Col (Col_h), rectangular Col (Col_r), or oblique Col (Col_ob) phases depending on the number/length of the peripheral flexible chains. The stabilization of the Col_ob phase, a less commonly found fluid columnar structure, and the first of its kind in TSAN systems, implies very intensive intermolecular (face-to-face) interactions among the TSAN cores within the column. The photophysical properties were investigated both in solution and the columnar states by UV–vis absorption and photoluminescence; markedly, the solution state emits light in the blue region. The light-emitting ability of the Col phase is particularly significant given the possibility that, in such cores, the protons and electrons interact with each other through the H-bonding environment