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 lightemitting diodes are also exemplified.

Elastography ultrasound (EUS) imaging is a vital ultrasound imaging modality. The current use of EUS faces many challenges, such as vulnerability to subjective manipulation, echo signal attenuation, and unknown risks of elastic pressure in certain delicate tissues. The hardware requirement of EUS also hinders the trend of miniaturization of ultrasound equipment. Here we show a cost-efficient solution by designing a deep neural network to synthesize virtual EUS (V-EUS) from conventional B-mode images. A total of 4580 breast tumor cases were collected from 15 medical centers, including a main cohort with 2501 cases for model establishment, an external dataset with 1730 cases and a portable dataset with 349 cases for testing. In the task of differentiating benign and malignant breast tumors, there is no significant difference between V-EUS and real EUS on high-end ultrasound, while the diagnostic performance of pocket-sized ultrasound can be improved by about 5% after V-EUS is equipped.

• Evaluating breast lesions with SE and CEUS could increase the diagnostic specificity • SE and CEUS offer alternatives to biopsy and possibly allow shorter-interval follow-ups • BI-RADS-US combined with CEUS exhibited the best diagnostic performance.