Novel Pyromellitic Diimide-Based Macrocycle with a Linear π-Electronic System and Bis(phenylethynyl)pyromellitic Diimide: Syntheses, Structures, Photophysical Properties, and Redox Characteristics

We report the syntheses, structures, photophysical properties, and redox characteristics of the [2 + 2] pyromellitic diimide-based macrocycle with a linear π-electronic system 2 as well as the 3,6-bis(phenylethynyl)pyromellitic diimide derivative 3. The interesting solid state structural properties of the clathrates of 3 with π-donors are also reported. The macrocycle 2 was synthesized by the direct cyclocondensation followed by the Sonogashira coupling reaction. X-ray crystallographic studies showed that the phenylacetylene moieties in 2 formed the intramolecular benzene dimer structures, and the bis(phenylethynyl)pyromellitic diimide moieties in both 2 and 3 were stacked in a parallel and slanted arrangement. Theoretical calculations for 2′ and 3 suggested the existence of electrostatic interactions between the bis(phenylethynyl)pyromellitic diimide moieties. The UV/vis spectral measurements and TDDFT calculations of 2, 2′, and/or 3 were performed to understand their electronic transitions. The fluorescence spectral measurements showed that 2 and 3 have visible fluorescence properties and 2 displays an excimer fluorescence at ca. 590 nm. The cyclic voltammetry measurements revealed that the electrostatic repulsion between the diimide moieties in 2 is greater than that in 1 according to the extension of the π-electronic systems. X-ray crystallography of the clathrates of 3 with various π-donors demonstrated the formation of the segregated donor−acceptor structures, indicating the strong aggregation ability of the bis(phenylethynyl)pyromellitic diimide moiety.