Rigidifying Fluorescent Linkers by Metal–Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

We
demonstrate that rigidifying the structure of fluorescent linkers
by structurally constraining them in metal–organic frameworks
(MOFs) to control their conformation effectively tunes the fluorescence
energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based
zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm
with a unity quantum yield (99.9 ± 0.5%) under Ar, representing
ca. 3600 cm–1 blue shift and doubled radiative decay
efficiency vs the linker precursor. An anomalous increase in the fluorescence
lifetime and relative intensity takes place upon heating the solid
MOF from cryogenic to ambient temperatures. The origin of these unusual
photoluminescence properties is attributed to twisted linker conformation,
intramolecular hindrance, and framework rigidity.