Quantum mechanics

Intramolecular force

Chemical physics

Photochemistry

Materials science

Two-photon absorption

Absorption (acoustics)

Two-photon excitation microscopy

Quantum yield

Stereochemistry

Polymer

Cross section (physics)

Photon

Laser

Physics

Nanotechnology

Organic chemistry

Planarity testing

Optics

Absorption cross section

Fluorescence

Conjugated system

Composite material

Crystallography

Chromophore

Chemistry

Covalent bond

Optoelectronics

Advanced Functional Materials

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 (104 GM). The finding highlights the synergy between sp 2 c‐conjugated framework and octupolar modules that leads to markedly improved TPA response owing to extended conjugated length, enhanced planarity and multidimensional intramolecular interaction. In view of the versatility of the branched chromophore, the proposed design idea is expected to be used to exploit more two‐photon active COF materials for a range of applications. Multiple uses of the COF in information encryption and warm white light‐emitting diodes are also exemplified.

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