Fluorescent Porous Organic Frameworks Containing Molecular Rotors for Size-Selective Recognition

Fluorescent porous materials have
been under intensive investigation
recently, because of their wide applications in molecular recognition
and chemical sensing. However, it is a great challenge to achieve
size selectivity and sensing linearity for molecular recognition.
Herein, we report a series of porous organic frameworks (POFs) containing
flexible tetraphenylethylene (TPE) moieties as molecular rotors with
responsive fluorescent behavior. These fluorescent POFs exhibit size-selective
turn-on fluorescence for the effective chemical sensing of volatile
organic compounds (VOCs), which can be attributed to the different
degrees of motion restriction of flexible TPE rotors by various VOCs,
leading to the partially freezing of rotors in more fluorescent conformations.
Significantly, a linear aggregation-induced emission (AIE) relationship
is observed between the fluorescent POFs and the VOCs over a wide
range of concentrations, which is highly beneficial for quantitative
sensing applications. The gas-phase detection of arene vapors using
POFs is also proven with unprecedentedly high sensitivity, selectively,
and recyclability. The mechanism of responsive fluorescence in POFs
is further investigated using molecular simulations and density functional
theory (DFT) calculations.