Supramolecular assemblies and redox modulation of pyromellitic diimide-based cyclophane via noncovalent interactions with naphthol

This paper reports the electroscopic and electrochemical properties of [2 + 2] pyromellitic diimide-based cyclophane 1 as well as acyclic N,N′-bis(2-methoxybenzyl)pyromellitic diimide 2 and the clathrate compounds formed by 1. Compound 1 was synthesized by direct cyclocondensation. Its structure was determined by an X-ray crystallographic analysis of a single crystal obtained by recrystallization from DMF. The intramolecular charge-transfer interactions of 1 and 2 were characterized by UV/vis spectroscopy and MO calculations. The UV/vis spectra showed that the tail of a longer wavelength absorption of both 1 and 2 reached the visible region. MO calculations (B3LYP/6-31G*) showed that the HOMO and LUMO orbitals of 1 and 2 substantially localize in the xylyl and pyromellitic diimide moieties across the methylene linker, respectively. The X-ray crystallographic analyses demonstrated that single crystals grown from a mixture of 1 and α-naphthol and a mixture of 1 and β-naphthol were the clathrate compounds with 1D and 2D supramolecular assemblies, respectively, which are formed by a combination of hydrogen-bonding and charge-transfer interactions. From the cyclic voltammetry measurements, both 1 and 2 showed reversible reduction processes, and the reduction potential observed at -1.09 V vs Ag/Ag⁺ for 2 split into two potentials at -1.01 and -1.14 V for 1. The addition of α- and β-naphthol induced a decrease in the potentials due to the diradical anion of 1 and radical anion of 2 by about 80 mV, and their reduction processes were reversible.