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 [E_T(30)].