Fabrication of flexibility-rigidity alternately assembled solid-state luminescence covalent organic frameworks: application to rifampicin antibiotics detection and latent fingerprint recognition.

To enhance the fluorescence properties of covalent organic frameworks (COFs) for broader applications, we introduce flexibility-rigidity alternately assembled red fluorescent COFs, named COF-MA. Its uniquely wide layer spacing (7.054 Å) significantly reduces π-π stacking interactions, suppressing fluorescence self-quenching and boosting solid-state emission. With long excitation and emission wavelengths, COF-MA exhibits minimal background interference, enabling highly sensitive detection of rifampicin (RFP) and rifapentine (RPT) in complex biological samples; the detection limits for both are 6.7 ng·mL. Combining experimental studies and computational simulations, we elucidated the fluorescence quenching mechanism. Furthermore, COF-MA-based fluorescent powder enabled rapid, high-contrast visualization of latent fingerprints on eight different substrates. This work not only proposes a novel structure-tuning strategy to improve COF fluorescence, but also delivers a stable probe for antibiotic detection and a versatile forensic tool, significantly expanding the practical scope of fluorescent COFs.