Well-Structured Narrow Near-Infrared Absorption Based on Nonaggregated Hexarylene-Bisimide toward a Colorless Dye

Extended π-conjugated systems are often insoluble, and their aggregation manner greatly affects their absorption spectra. This study produced a planar, soluble, and nonaggregated hexarylene-bisimide (<b>HB</b>) with appropriate substituents. The single-crystal X-ray structure of <b>HB</b> confirmed the planar molecular structure with small twist angles and the dimerization behavior of <b>HB</b> in the solid state. The concentration-dependent ¹H NMR experiments in CDCl₃ indicated that the association constant <i>K</i>_dimer is 4.6 × 10³ M^-1 at 298 K and Δ<i>G</i>_dimer (298 K) = -20.8 kJ mol^-1. The longest absorption of <b>HB</b> at the monomeric state exhibits a sharp and intense peak at 921 nm (ε = 230,000 M^-1 cm^-1, full width at half-maximum = 718 cm^-1) in toluene. 75% of the absorption of <b>HB</b> above 400 nm appears in the near-infrared region, thus giving a practically colorless solution. Magnetic circular dichroism spectra of a series of oligorylene-bisimides reveal the predominant contribution of the linear polyene-like conjugation over the annulene-like conjugation for larger [<i>n</i>]oligorylene-bisimides.