Engineering linkage as functional moiety into irreversible thiourea-linked covalent organic framework for ultrafast adsorption of Hg(II).

Development of novel functionalized covalent organic frameworks (COFs) as adsorbent for removal of mercury from environment is of great significance, but the conventional strategies for functionalizing COFs always sacrifice porous properties and suppress the exposure of functional sites, which goes against the rapid adsorption of Hg(II). Here, we show the rational design and preparation of the first thiourea-linked COFs via engineering the COFs linkage as functional moiety for ultrafast and selective adsorption of Hg(II). Two thiourea-linked COFs JNU-3 and JNU-4 were prepared via tautomerism reaction of 1,3,5-triformylphloroglucinol with 1,4-phenylenebis(thiourea) and 1,4-biphenylenebis(thiourea), respectively. The thiourea serves as not only linkage to connect the building block into irreversible crystalline structure, but also functional moiety to give no occupation of the COF pore and full exposure to Hg(II) with strong affinity, offering the JNU-3 and JNU-4 large adsorption capacity (960 and 561 mg g-1, respectively) and ultrafast kinetics (equilibrium time of 10 s) for Hg(II). The proposed strategy for the design of functional COFs with inherent linkage as functional moiety largely promotes the performance of COFs for diverse applications.

Aggregation-Switching Strategy for Promoting Fluorescent Sensing of Biologically Relevant Species: A Simple Near-Infrared Cyanine Dye Highly Sensitive and Selective for ATP.

We report a strategy for enhanced performance of fluorescent sensing of biologically relevant species that often bind with natural receptors via multiple interactions. We propose making a fluorescent sensory molecule to form H-aggregates such that its emission is quenched leaving a low background, and upon binding to a biologically relevant species, the aggregate switches to another form in which the fluorescent species is better protected to afford a stronger emission signal. Meanwhile, the aggregated fluorescent dyes afford multiple interactions with the sensing species that require multiple binding sites. The lower background, stronger binding, and stronger signal would therefore lead to a much higher sensing performance, as improved selectivity would also result in along with the signal amplification. We thus designed a near-IR cyanine dye bearing two boronic acid groups (Cy-BA) for fluorescent sensing of ATP such that the boronic acid groups in the dye molecule bind to the cis-diol moiety in ATP. Introduction of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) below its critical aggregation concentration is key because Cy-BA molecules made into H-aggregates were practically nonfluorescent. Upon mixing with ATP, a dramatic enhancement in the fluorescence occurred because of the formation of ATP/Cy-BA/DTAB vesicles in which the fluorescent dye is well dispersed and protected. This sensing scheme, despite the dynamic nature of the boronic acid/cis-diol interaction, weakness of the electrostatic interactions among ATP/Cy-BA/DTAB, and poor selectivity of these interactions, allows for highly sensitive and selective detection of ATP in aqueous solution.

Helical Aggregates of Building Blocks Formed In†Situ from Five Components.

Reported here is the induced helical aggregation of an achiral cationic perylene-3,4-dicarboximide (1) that contains a phenylboronic acid group, together with UMP that bears a cis-diol moiety able to interact with boronic acid and an imide group known to coordinate with Hg2+ . In selected solvents, 1 exists in monomer form, even in the presence of either UMP or Hg2+ . Helical aggregation only takes place if 1 is mixed with both UMP and Hg2+ , which is shown to result from the formation of a building block consisting of five components in the form 1-U-Hg2+ -U-1. Strong exciton-coupled circular dichroism signals were observed in the absorption window of the achiral dye chromophore, demonstrating the transfer of the chirality of UMP to the supramolecular aggregates of P-helicity. Synergism was shown to occur upon aggregation of the 1-U-Hg2+ -U-1 building block, as substantially enhanced affinity and binding selectivity were observed for UMP and Hg2+ , despite the otherwise weak and less selective interactions of 1-UMP and UMP-Hg2+ . In support of this synergism, the g-factor of the aggregates was found to be 1.4×10-2 , which represents a high value. We thus show a strategy of in situ construction of a building block from multiple components, among which the interactions can be weak and less selective. Therefore, the design and syntheses of the constituent components are substantially simplified, yet diverse functions can be expected from their supramolecular aggregates.