Tunable Stimuli-Responsive Luminescence From Covalent Organic Frameworks Displaying Vibration-Induced Emission

Introducing dynamic components that couple molecular motion with optical output offers a promising strategy for developing stimuli-responsive luminescent covalent organic frameworks (COFs). Vibration-induced emission (VIE) molecules are particularly attractive dynamic luminophores, as their excited-state bent-to-planar conformational evolution enables dual emission, large Stokes shifts, and environment-regulated fluorescence. However, VIE-based COFs have not yet been reported. Herein, we report two VIE-based three-dimensional COFs, JUC-735 and JUC-736, constructed from a symmetric N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC)-derived building block with a saddle-shaped conformation. Both COFs exhibit high crystallinity, thermal stability, and well-defined porosity. Photophysical studies reveal that the excited-state conformational evolution of DPAC remains operative in these crystalline environments, leading to dual emission with exceptionally large Stokes shifts in solution (> 300 nm; 14526 cm^{- 1} for JUC-735 and 14272 cm^{- 1} for JUC-736). This dynamic emission behavior further enables tunable luminescence responses to aggregation, viscosity, and pressure. Notably, JUC-736 shows more pronounced dual-emission modulation under aggregation, near-white-light emission tuning, and reversible multicolor piezofluorochromism, whereas JUC-735 mainly exhibits long-wavelength emission modulation with higher intensity sensitivity. These results highlight the important role of the local framework environment in regulating the stimuli-responsive emission behavior of dynamic chromophores, providing a working strategy for designing multi-stimuli-responsive luminescent COF materials.