Recognition mechanism of molecularly imprinted polymers by aggregation-induced emission

Research on molecularly imprinted polymers (MIPs) has long been receiving much attention, but issues concerning the recognition mechanism and how the impact factors work are still far from clear. In this work, we studied the imprinting and recognition procedures from a new perspective. Two factors that have a major impact on the imprinting performance were studied separately: one is the functional groups (FGs) of the template and the other is the size of the template. A series of aggregation-induced emission molecules (AIEgens) was employed as the templates, and they were selected elaborately, one group of which having different functional groups with a similar size, while the other being different in molecular size. It was found that the MIP was inclined to combine with molecules with more effective functional groups or with smaller sizes. Meanwhile, the more ordered sites and the larger cavities in the polymers afforded the MIP with better adsorption performance. The binding energy (DE) and the mechanism at the molecular level between templates and polymers were analyzed by using density functional theory (DFT) calculations, and the results were consistent with experimental results in the aspect of the FG effect. In addition, the unique luminescence properties of AIEgens allow for visible observation of the change of the template within the polymer during preparation and rebinding processes. More importantly, quantification of template molecules during the adsorption process was fulfilled based on their solid-state fluorescence intensities, which opens a new door for AIEgen application. A comparison with the common method of UV-vis spectrometry revealed that solid-state fluorescence measurement has the advantages of direct detection, easy operation, a wide linear range and so on.