Synthesis and Properties of a Decacyclene Monoimide and a Naphthalimide Derivative as Three-Dimensional Acceptor-Donor-Acceptor Systems

Abstract

A method involving the Diels-Alder (DA) cycloaddition of diacenaphtheno[1,2-b;1',2'-d]thiophenes (DATs) with N-alkylacenaphthylene-5,6-dicarboximides (AIs) was developed to synthesize decacyclene monoimides (DCMIs). The reactions generate the corresponding 1:2 adducts (BAIAs) as major products together with 1:1 adducts (the DCMIs). The molecular structure of BAIAb (N-octyl derivative) was unambiguously assigned as the bis-adduct having an endo,endo spatial disposition of the two acenaphthylene-5,6-dicarboximide moieties by using X-ray crystallographic analysis. Relative to the absorption spectrum of decacyclene triimide (DCTIa, N-2-ethylhexyl derivative), that of the analogous N-2-ethylhexyl-substituted monoadduct, DCMIa, is bathochromically shifted despite the fact that it possesses a less delocalized π-electron system. DCMIa does not fluoresce in various organic solvents, whereas DCTIa emits yellow fluorescence in CH₂ Cl₂ with a low quantum yield (Φ_SN ). Moreover, DCMIa in CDCl₃ displays concentration-dependent ¹ H NMR spectroscopy behavior, which suggests that it self-aggregates with an association constant (K_a ) of (193±50) m^-1 at 20 °C. Despite the presence of four bulky tert-butyl groups in DCMIa, its K_a value for aggregate formation is comparable to that of DCTIa [(495±42) m^-1 ], which does not contain tert-butyl substituents. Spectroscopic studies with the bis-adduct BAIAa (N-2-ethylhexyl derivative) show that it displays remarkable solvatofluorochromism corresponding to an emission maximum shift (Δλ_EM ) of 100 nm. The results of density functional theory calculations on BAIAc (N-methyl derivative) demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficient distributions, which indicates that the ground-to-excited state transition of the novel three-dimensional acceptor-donor-acceptor BAIAa system should have intramolecular charge-transfer character.

Keywords: aggregation; charge transfer; cycloaddition; donor-acceptor system; solvatochromism.