[supramolecular] there are more responsive materials in the environment. Have you ever seen that pH changes the charge?

Different from the content of traditional molecular chemistry, supramolecular chemistry pays more attention to the molecules linked by weak intermolecular interaction and the aggregates composed of them, which usually have nanometer scale and can be assembled by supramolecular- In the process of disassembly, the structure and function change Therefore, a large number of structures based on supramolecular assembly, including vesicles, micelles, linear polymers, electrospun fiber structures, nanotubes, cyclic polymers and layer by layer assembly structures, can pass through external environmental conditions (such as pH The reversible transformation was realized under the conditions of value, temperature, ionic strength, redox potential, light, electricity, magnetic field, ultrasound, etc With the development and diversification of stimulus responsive or environmentally sensitive materials, they have been widely used in artificial membrane ion channels, intelligent drug controlled release systems, virus inhibitors, dispersion of carbon materials, detection and adsorption of pesticide and other drug molecules, construction of metal organic framework, stability of gold nanoparticles and selective adsorption and separation of gases Pan Recently, the research group of Samuel I stump, Professor of Northwestern University, reported a water-soluble super molecule perylene monoimide carboxylate This perylene monoimide with hydroxyl can exhibit different properties in different acid-base solutions due to the ionization of hydroxyl: the system can be assembled into a size of about 500 * 50 * 2 under acid conditions In the alkaline condition, because of the increase of repulsion force between molecules, only a few nanoribbons can be formed This achievement was published in Chemical Science (DOI: 10.1039 / c8sc05595e) under the title of "impact of charge switching stimuli on supramolecular perylenemonoide assemblies" Fig 1 Synthesis of perylene diimide 1 and 2 (picture source: chem SCI.) perylene diimide synthesis is not complex (Fig 1) For 1, the author first coupled perylene diimide derivative S1 containing bromine with water to obtain the intermediate containing hydroxyl, and then protected the hydroxyl on the intermediate with TBS to obtain S2 In the presence of sulfuric acid, perylene diimide 1 containing carboxyl group and hydroxyl group was obtained The synthesis of reference compound 2 is to brominate perylene diimide derivative S3 to obtain perylene diimide derivative S4 with similar structure to S1, and then carry out the same reaction to obtain 2 After obtaining perylene monoimide, the photophysical properties of perylene monoimide were studied first (Fig 2) The results show that 1 and 2 are blue in alkaline solution and reddish brown in acid solution It is speculated that the reason is that the hydroxyl groups of perylene diimide are ionized in the alkaline condition, so the stacking behavior of perylene diimide in solution is changed In addition, X-ray diffraction was used to characterize 1 in different acid-base solutions, and the corresponding size was calculated The results show that 1 exhibits a high degree of order in acid condition, and its domain size is about 476 Å, which is equivalent to the superposition of 142 perylene monomers In alkaline condition, the order of 1 is relatively low, and its domain size is only 33 In other words, there are only about 11 perylene monomers Fig 2 Structure, color and UV spectrum of perylene diimide 1 and 2 in different acid-base solutions (picture source: chem SCI.) since perylene diimide monomer can be used for photosensitizer research, the author would like to know whether the ionization of hydroxyl will change the electronic energy level of the molecule The HOMO energy levels of molecule 1 were measured by using the ultraviolet photoelectron spectroscopy (UPS) (Fig 3), and their band gaps were calculated by the data of UV absorption spectrum The results showed that 1 not only showed different electronic energy levels under different pH, but also could be used as photosensitizer Figure 3 Energy level diagram of 1 at different pH and its application as photosensitizer (photo source: chem SCI.) full text author: Adam dannehoffer, Hiroaki Sai, dongxuhuang, Benjamin nagasing, Boris harutyunyan, Daniel J Fairfield, Taner aytun, Stacey M chin, Michael J bedzyk, Monica Olvera de la cruzab and Samuel i.stump.