Layer Sliding-Induced Fluorescence Changes in a Flexible Hydrogen-Bonded Organic Framework

Flexible hydrogen-bonded organic frameworks (HOFs) capable of changing their fluorescence properties upon structural transformation have gained much attention, while their design strategies have not been established. Herein, we demonstrate that sliding of the robust hydrogen-bonded 2D layers can induce dynamic emission color changes of HOFs. Layered HOF CP-tBPy-1, which is composed of tert-butylpyrene derivative with four carboxyphenyl groups (CP-tBPy), transformed to another crystalline form, CP-tBPy-2, upon release of guest solvent molecules. Single-crystal X-ray diffraction analysis revealed that the sliding of the layers changed the pyrene cores from monomeric to dimeric species, giving rise to fluorescence color changes from blue to green. Fluorescence spectroscopy and single-crystals microscopy disclosed details of the photobehaviors of these HOFs. These results are the first example of fluorescence changes of HOFs due to sliding of hydrogen-bonded 2D network layers, providing a new design strategy to construct functional fluorescent porous materials.