Synthesis, optical properties and self-assemblies of three novel asymmetrical perylene diimides modified with functional hydrogen bonding groups at bay positions

Abstract

Three new perylene diimide derivatives PDI-NH₂, PDI-OH and PDI-COOH modified with functional hydrogen bonding groups at bay positions by ethynyl bridges were successfully synthesized via Pd-catalyzed Sonogashira couplings. The structures were characterized by ¹H-NMR, MS, and FT-IR. The photophysical properties were studied by UV-Vis absorption and fluorescence spectroscopy, and the three PDIs showed typical pronounced aggregation in the film state. PDI-NH₂ showed “off–on” fluorescence behavior upon the addtion of trifluoroacetic acid due to the inhibition of photoinduced electron transfer between the PDI core and the phenylamine moiety. In addition, we studied the self-assembly behaviors of PDI-NH₂, PDI-OH and PDI-COOH on the HOPG surface by using STM. PDI-NH₂ and PDI-COOH formed a dumbbell-shaped dimer with a zigzag ridge structure and a linear ridge structure, respectively. PDI-OH first formed a dumbbell-shaped dimer and furthermore six dimers are connected head to tail to form a flower-shaped hexagonal 2D porous self-assembled structures. Cyclic voltammograms (CVs) were investigated. The LUMO energy levels of PDI-NH₂, PDI-OH and PDI-COOH are −3.89 eV and the HOMO energy levels are −5.76 eV, −5.97 eV and −6.05 eV, respectively. The highly ordered supermolecular self-assembly monolayers and outstanding photophysical–electrochemical properties endow the three novel PDIs with good potential for application in organic devices such as organic field-effect transistors, solar cells and so on.