Crystalline porous
materials such as covalent organic frameworks
(COFs) are advanced materials to tackle challenges of catalysis and
separation in industrial processes. Their synthetic routes often require
elevated temperatures, closed systems with high pressure, and long
reaction times, hampering their industrial applications. Here we use
a traditionally unperceived strategy to assemble highly crystalline
COFs by electron beam irradiation with controlled received dosage,
contrasting sharply with the previous observation that radiation damages
the crystallinity of solids. Such synthesis by electron beam irradiation
can be achieved under ambient conditions within minutes, and the process
is amendable for large-scale production. The intense and targeted
energy input to the reactants leads to new reaction pathways that
favor COF formation in nearly quantitative yield. This strategy is
applicable not only to known COFs but also to new series of flexible
COFs that are difficult to obtain using traditional methods.
Conventional
aromatic compounds tend to exhibit the formation of
sandwich-shaped excimers and exciplexes between their excited and
ground states at high concentrations or in their aggregated states,
causing their fluorescence to weaken or disappear due to the aggregation-caused
quenching (ACQ) effect. This limits their applications in concentrated
solutions or solid materials. Herein, for the first time, ACQ-based
pyrene (Py) units are covalently connected to the surface of polyethylene/polypropylene
nonwoven fabric (PE/PP NWF) via electron beam preradiation-induced
graft polymerization followed by chemical modification. The matrix
can be considered a solid solvent and Py units as a solid solute,
such that the amount of Py units can be controlled by varying the
reaction time. The obtained fluorescent fabric not only exhibits remarkable
fluorescence properties with high fluorescence intensity, high quantum
yield (>90%), and excellent fluorescence stability after laundering
or in harsh chemical environments, but the fluorescence color and
intensity, quantum yield, and lifetime can also be regulated by employing
the ACQ effect. Additionally, the as-prepared fluorescent fabric can
effectively distinguish common monocyclic aromatic hydrocarbons via
a simple fluorescence response test.
Luminescent covalent organic frameworks (COFs) find promising applications in chemical sensing, photocatalysis, and optoelectronic devices, however, the majority of COFs are non or weakly emissive owing to the aggregation‐caused quenching (ACQ) or the molecular thermal motion‐based energy dissipation. Here, we report a previously unperceived approach to improve luminescence performance of COFs by introducing isotope effect, which is achieved through substitution of hydrogen from high‐frequency oscillators X‐H (X=O, N, C) by heavier isotope deuterium. Combining the “bottom‐up” and in situ deuteration methods generates the first deuterated COF, which exhibits an impressively 19‐fold enhancement in quantum yield over that of the non‐deuterated counterpart. These results are interpreted by theoretical calculations as the consequence of slower C/N‐D and OD⋅⋅⋅O vibrations that impede the nonradiative deactivation process. The proposed strategy is proved applicable to many other types of emissive COFs.
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