Multibranched Octupolar Module Embedded Covalent Organic Frameworks Enable Efficient Two‐Photon Fluorescence

Abstract Covalent organic frameworks (COFs) have emerged as potential light emitting polymers for optoelectronic and optical devices, but their nonlinear optical properties, particularly two‐photon absorption and fluorescence (TPA/TPF), have seldom been explored. Herein, to construct octupolar three‐branched modules (e.g., acceptor 3‐(donor‐core), triphenylbenzene core) within a 2D cyano‐sp 2 c‐conjugated framework is proposed that results in two‐photon luminescent COFs, combining a large TPA cross section and high quantum yield (QY). Such octupolar module‐embedded sp 2 c‐conjugated COFs emit not only intense one‐photon fluorescence with QY of 27.2% in the solid state and 38.1% in tetrahydrofuran—superior to almost all reported COFs, but also efficient two‐photon fluorescence with large TPA cross section of 1225 GM—remarkably surpassing the corresponding cyano‐sp 2 c‐linked model compounds…