New thermotropic dyes based on amino-substituted perylendicarboximides

We report on an facile multigram synthesis of novel thermotropic dyes. When these dyes are heated they undergo an irreversible change from a photostable primary color to a photostable secondary color. Our concept is based on thermally initiated fragmentation to afford a chromophore with a donor and an acceptor substituent. We used thermally unstable alkoxycarbonyl substituents as masking groups for the strong electron-donating primary amino group attached to a perylenedicarboximide chromophore. On heating the alkoxycarbonylated dyes, the parent primary amino-functionalized dyes are regenerated in almost quantitative yield by elimination of an alkene and carbon dioxide. This process is accompanied by a large bathochromic shift in the absorption spectrum. Variations in the alkoxycarbonyl substitution lead to different reaction temperatures for the color change in this class of materials. The synthetic route used for the amino-functionalized perylene imide dyes involves the palladium-catalyzed amination of bromo-substituted precursors.