Anomalous deep-red luminescence of perylene black analogues with strong π-π interactions

Abstract Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close π−π stacking arrangement. However, contrary to the luminescent monomers, deep-red and black PBI pigments are commonly non- or only weakly fluorescent due to (multiple) quenching pathways. Here, we introduce N -alkoxybenzyl substituted PBIs that contain close π stacking arrangement (exhibiting d π−π ≈ 3.5 Å, and longitudinal and transversal displacements of 3.1 Å and 1.3 Å); however, they afford deep-red emitters with solid-state fluorescence quantum yields ( Φ F ) of up to 60%. Systematic photophysical and computational studies in solution and in the solid state reveal a sensitive interconversion of the PBI-centred locally excited state and a charge transfer state, which depends on the dihedral angle ( θ ) between the benzyl and alkoxy groups. This effectively controls the emission process, and enables high Φ F by circumventing the common quenching pathways commonly observed for perylene black analogues.