1,3,6,8-Tetraphenylpyrene derivatives: Towards fluorescent liquid-crystalline columns?

Tetraphenylpyrene has been selected as a discotic core to promote liquid-crystalline fluorescent columns in view of its high fluorescence quantum yield in solution and ease of substitution by flexible lateral side chains. The synthesis and characterization of ten new derivatives of pyrene have been carried out; the pyrene core has been substituted at the 1,3,6,8-positions by phenylene rings bearing alkoxy, ester, thioether, or tris(alkoxy)benzoate groups on the para position; the compounds have been characterized by mass spectrometry and ¹HNMR and UV-vis spectroscopies. In order to generate liquid-crystalline phases, the nature, number, and size of the side chains as well as the degree of polarity around the tetraphenylpyrene core have been varied. However, the desired liquid-crystalline behavior has not been observed. The supramolecular order together with the absorption and emission properties in solution and the solid state are discussed and compared to theoretical predictions. Quantum-chemical calculations rationalize the high solid-state fluorescence of a tetraphenylpyrene derivative for which the crystal structure has been determined.