Composites of Perylene Chromophores and Layered Double Hydroxides: Direct Synthesis, Characterization, and Photo- and Chemical Stability

Brilliantly coloured pigments can be obtained by direct synthesis when layered double hydroxides (see Figure) are precipitated under controlled conditions in the presence of an organic perylene dye. The figure shows the structural arrangement of the dye molecules between the hydroxide layers. The stability of these organic–inorganic composite structures is not diminished compared to the pristine dye in a harsh application environment.

Abstract

Composites of the tetra-anion of the perylene dye N,N′-di(phenyl-3,5-disulfonic acid)perylene-3,4:9,10-tetracarboxydiimide (PBITS) with layered double hydroxides (LDHs) were formed by direct synthesis (co-precipitation at constant pH). The LDHs were of the hydrotalcite (Mg–Al–OH and Zn–Al–OH compositions). During synthesis of the hydrocalumite type (Ca–Al–OH), partial destruction of the dye occurs, being more pronounced at higher pH values. The composites were characterized with regard to their composition by elemental and thermal analysis. From UV-vis spectroscopic data and powder X-ray diffraction, a structural model is developed for the composites. In the galleries between the hydroxide layers, the chromophore molecules are stacked in an J-type arrangement. The compounds have brilliant colors and are insoluble in common solvents. With regard to a possible application as pigments, their photostability and their chemical resistance against a typical application environment was tested. The photostability of the dye molecules and their chemical resistance against setting cement are slightly raised by the occlusion within the LDH structure; however, the photostability of the LDH–cement is lower than that of cement colored with the pure perylene dye.