Controlling the swelling properties of hydrogels is of primary importance for many applications ranging from actuators and valves to tissue engineering and drug delivery.Herein, we report the use of cyclobis(paraquat-p-phenylene) (CBPQT 4+ , 4X -) as a versatile host 2 to finely tune the swelling behavior of 1,5-dialkyloxynaphthalene guest containing poly(N,Ndimethylacrylamide) hydrogels (NaphtGelz) through supramolecular host-guest complexation.While the equilibrium swelling of NaphtGelz in water decreases with increasing amount of hydrophobic naphthalene groups, the opposite behavior is observed with superabsorbing behavior (up to 180 times their initial dry mass) upon immersion in aqueous solutions containing the macrocyclic CBPQT 4+ ,4Xdue to formation of tetracationic host-guest complexes. In this case, the swelling amplitude could be conveniently programmed either by variation of the naphthalene content of the hydrogels or by controlling the stoichiometry of the host-guest binding events. Furthermore, by modifying the nature of the counter-ions (X = Cl -, Br -, I -) of the tetracationic CBPQT 4+ macrocyclic host, the swelling of the hydrogels could be tuned in line with Pearson's absolute hardness scale of X -. The swelling behavior of these supramolecular hydrogels could be successfully described by a theoretical model taken into account the hydrophobic association of the naphthalene groups and their screening by host-guest complexation. Finally, addition of SDS (Sodium Dodecyl Sulfate) as surfactant to the supramolecularly swollen hydrogels led to a large decrease in hydrogel size due to dissociation of the host-guest complexes and the formation of CBPQT 4+ ,4DSwithin the hydrogel.

The regulation of the concentration of aw ide range of smallm olecules is ubiquitousi nb iologicals ystems because it enablesthem to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetics ystem that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene)h ost (BBox)a nd a 1,5-dialkyloxynaphthalene (DNP)g uest attached to aw elldefineddual responsive copolymer composed of N-isopro-pylacrylamidea st hermoresponsive monomer and acrylic acid as pH-responsive monomer.C ontrolled, partialr elease of the BBox,e nabling control over its concentration, is based on the tunablep artial collapseo ft he copolymer.T his colored supramolecular assemblyi so ne of the first synthetic systems providing control over the concentration of as mall molecule, providing great potential as both Tand pH chromic materials and as ab asis to develop more complex systems with molecular communication.

Temperature is among the most important measured physical parameters. Despite that numerous polymeric temperature sensors having been reported, none of these systems can record the time that the object was heated to a certain temperature. Here, we report a supramolecular approach for developing a smart polymeric hydrogel capable of measuring the temperature and the duration of the heat exposure. This double memory principle is based on dual kinetic control of the dissociation of cyclobis(paraquat-p-phenylene) tetrachloride (CBPQT 4+ ,4Cl – )-naphthalene host–guest complexes within a thermoresponsive naphthalene functionalized poly(N-isopropylacrylamide) hydrogel. Heating-induced collapse of this LCST polymer hydrogel induces host–guest complex dissociation, followed by the diffusion-controlled release of the free CBPQT 4+ ,4Cl – host into the medium surrounding the hydrogel. This partial host release is governed by the heat exposure time and the heating temperature that controls the extent of dehydration of the hydrogel and, thus, the diffusion rate of the CBPQT 4+ ,4Cl – . Hence, the amount of host released is an indicator for both the heating temperature and the heating time of the hydrogel and can be recorded by determining the reswelling capability of the hydrogel in water. As such, measuring the reswelling capability provides information on how long the hydrogel system was exposed to a certain temperature.