Synthesis, reaction, and optical properties of cyclic oligomers bearing 9,10-diphenylanthracene based on an aromatic tertiary amide unit

Abstract

Novel cyclic aromatic amide oligomers containing highly fluorescent 9,10-diphenylanthracene units were prepared by condensation of a monomer with amino and ester functional groups using lithium bis(trimethylsilyl)amide. The cyclic trimer (C3A, 40%) and tetramer (C4A, 8%) were isolated using preparative gel permeation chromatography. Some of the aromatic proton signals derived from anthracene were observed in the upfield region (6.96–6.87 ppm) in the 1H nuclear magnetic resonance spectrum of C3A. X-ray crystallographic analysis indicated that three anthracene moieties are inclined with respect to the cyclic skeleton and partly overlap each other. The fluorescence peak maximum of C3A (438 nm) showed a small red-shift compared with that of an acyclic model compound (425 nm). Reduction of the amide carbonyl group in C3A gave the cyclic trimer HC3A, which has a tertiary amine unit. The fluorescence peak maximum of HC3A (489 nm) was largely red-shifted from that of C3A and exhibited strong solvent dependence. A linear correlation was observed between the Stokes shift (Δν), ranging from 2981 to 6646 cm−1, and the Reichardt's solvent polarity parameter [ET(30)].