Anomalous deep-red luminescence of perylene black analogues with strong $\pi$-$\pi$ interactions
Nat. Commun., 14 (1):
1922 (Apr 6, 2023)DOI: 10.1038/s41467-023-37171-y
Abstract
Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close $\pi$−$\pi$ 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 $\pi$ stacking arrangement (exhibiting d$\pi$−$\pi$ ≈ 3.5þinspace\AA, and longitudinal and transversal displacements of 3.1þinspace\AA and 1.3þinspace\AA); however, they afford deep-red emitters with solid-state fluorescence quantum yields ($\Phi$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 ($þeta$) between the benzyl and alkoxy groups. This effectively controls the emission process, and enables high $\Phi$F by circumventing the common quenching pathways commonly observed for perylene black analogues.