Organic semiconductor frameworks integrating bay-substituted perylene bisimides as screw dislocation units in onion-like π–π stacked architectures

Abstract

Imine-linked covalent organic frameworks (COFs) are built with precision chemistry control, where the tetra-p-CHO-aryloxy bay-substituted PBI-1 serves as a rylene chromophore subunit encoding (i) a broad visible light cross-section (ε_{λ552 nm} = 42 000 L mol⁻¹ cm⁻¹); (ii) an excited state redox manifold (E(PBI-1^*/·—) = 1.82 V vs. NHE, E(PBI-1^·+/*) = −0.43 V vs. NHE); (iii) a dynamic chiral distortion of the aromatic core with a dihedral angle of up to 33°; and (iv) two tertiary amines as N-imide terminals favoring proton-coupled charge transfer mechanisms in aqueous media. PBI-1-COFs are designed herein following an isoreticular expansion strategy based on the elongation of polyaryldiamine linkers (n = 1–3 as Ph, bPh, and tPh), where convergent FT-IR, ssNMR, PXRD, TEM and SEM evidence points to a slip-stacked arrangement of the 2D-COF layers, likely induced by the conformational distortion of the PBI-1 cores, resulting in a prevalent J-type coupling scheme and a distinct red-shift of the material absorption (up to 700 nm), optical bandgaps of ∼1.9 eV, and a morphological progression from onion-like, curved π–π stacked domains to fully folded spheroidal structures (quasi-monodispersed particles with D = 700 ± 100 nm). In situ polymerization of high surface area 3D-tungsten oxide nanosheets (WO₃ 3D-NS) affords robust photoanodes integrating the n-type COF semiconductor layer capable of record photocurrent outputs (up to 590 ± 50 μA cm⁻²) under green-light irradiation (1 sun, λ > 490 nm), probed with anionic hydroquinone shunts (an applied bias of 0.8 V vs. RHE) and favored by a preferential host–guest response due to complementary charge interactions mapped by NMR-DOSY and FT-IR spectroscopy.