The Design, Synthesis and Study of Long-Wavelength Absorbing Ionic Perylenebis(dicarboximide)s as Chromonic Mesogens
AuthorAryal, Gyan Hari
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A series of long-wavelength absorbing and emitting perylenebis(dicarboximde)s were designed and synthesized by introducing different number and types of amino-substituents on the perylene-core and the electro-optical properties were investigated by UV-vis and fluorescence spectroscopy. A significant bathochromic shift of &lambda<sub>max</sub> was achieved in mono- and di-amino substitututed compounds <bold>1.2</bold>, <bold>1.3a-b</bold> and <bold>1.4a-b</bold> compared with the unsubstituted analogue <bold>1.1</bold>. Perylene core substituted compounds showed reduced aggregation in aqueous solution compared with unsubstituted analogue. The absorption and fluorescence properties of compounds with <italic>N</italic>,<italic>N</italic>-diethylamino groups also vary with solvent polarity and acidity. However, the absorption spectra of the quaternized compounds showed a very little change with increased pH.The structural effect on aggregation and liquid-crystalline properties of their ionic derivatives <bold>1.1a-b</bold>, <bold>1.2a-d</bold>, <bold>1.5a-f</bold>, and <bold>1.6a-b</bold> in aqueous solution were studied by UV-vis spectroscopy, polarized microscopy, and (or) <super>2</super>H NMR spectroscopy. The <super>2</super>H NMR data were also used to calculate the order parameter and compared with previously studied compounds. In general, the core substituted compounds form chromonic liquid crystals at room temperature at higher concentrations compared to those of the unsubstituted analogues. The liquid-crystalline properties of these compounds in water also vary with the size and the nature of counterions: formate and chloride salts. Furthermore, oriented solid films were prepared by the mechanical shearing of the liquid-crystalline N phase of <bold>1.1a-c</bold>, <bold>1.2a-b</bold> and <bold>1.2d</bold>, and analyzed by polarized microscopy and polarized UV-vis spectroscopy, which showed the direction-dependent absorption properties. Broad-spectrum absorbing films were prepared by mixing two compounds with different absorption properties. This research has demonstrated that the optical and chromonic liquid-crystalline properties of these compounds in aqueous solution as well as the optical properties of their sheared films can be controlled at the molecular level by designing the molecular structures of the chromonic mesogens.