Abstract
Aggregation-induced emission (AIE) molecules are nonemissive in dilute solution but emit intensely upon aggregation in complete contrast to aggregation-caused quenching (ACQ) molecules. The emission of ACQ molecules, such as fluorescein, that have been encapsulated into the hydrophilic nanopores in a cyclodextrin-based metal-organic framework (CD-MOF) was reported to be enhanced due to the disappearance of concentration quenching and the restriction of thermal motion. However, the contribution of the restriction of thermal motion in CD-MOF could not be elucidated. In this study, an AIE-active L-cysteine/Au(I) (L-Cys/Au(I)) complex was synthesized and introduced into the nanopores of CD-MOF via a co-crystallization method. We determined the amount and chemical composition of the L-Cys/Au(I) complex in CD-MOF. The fluorescence intensity of the L-Cys/Au(I)@CD-MOF composite was investigated. The L-Cys/Au(I) complex that was synthesized from Au(III) chloride and L-cysteine was found to be a linear oligomer consisting of Cys5Au4. For the L-Cys/Au(I)@CD-MOF composite with a L-Cys/Au(I) complex of 0.45 per hydrophilic nanopore, the total fluorescence intensity of the isolated L-Cys/Au(I) complex in CD-MOF exceeded that of the L-Cys/Au(I) complex in the solid-state due to the restriction of the thermal motion without the aggregation of the complex.
Highlights
Aggregation-induced emission (AIE) is a unique photophysical phenomenon that is completely opposed to the aggregation-caused quenching (ACQ) effect observed in typical luminophore systems
If AIE-active molecules can be introduced into the cyclodextrin-based metal-organic framework (CD-MOF), the fluorescence intensity will increase due to the suppression of thermal motion, without considering the effects of concentration quenching
When a similar fluorescence experiment was conducted using CD-MOF that 7was encapsulated with fluorescein [10], the fluorescence intensity decreased with increasing fluorescein concentration
Summary
Aggregation-induced emission (AIE) is a unique photophysical phenomenon that is completely opposed to the aggregation-caused quenching (ACQ) effect observed in typical luminophore systems. The AIE fluorogens are non-luminescent in a dilute solution but emit intensely upon aggregation formation. Their aggregates show strong fluorescence mainly due to the restriction of their thermal motion in the aggregate state. Metal cations that are smaller than the ring size of silica network structure can penetrate through the shell light up the glutathione/Au(I) complex via the AIE mechanism. Isolated Flu and Rh B molecules emitted strong yellow and red fluorescence, respectively, in the solid-state due to the disappearance of concentration quenching and the restriction of thermal motion. If AIE-active molecules can be introduced into the CD-MOF, the fluorescence intensity will increase due to the suppression of thermal motion, without considering the effects of concentration quenching
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