Construction Of A Cup-pyrrole Fluorescent Supramolecular Assembly And Its Sensing Application

Supramolecular chemistry,which exploits the reversible nature of noncovalent interactions,has proved especially useful in the construction of self-assembled and responsive materials.Host-guest chemistry based upon the macrocyclic compounds,plays a pivotal role in the supramolecular chemistry.Macrocyclic compounds,such as crown ethers,cyclodextrins(CD),calixarenes,and cucurbiturils(CB),have attracted increasing attention among researchers in various disciplines due to their large cavity volume.Moreover,macrocyclic compounds have been widely used in the fields of supramolecular soft materials,drug delivery systems and photothermal conversion materials.In general,as host molecules,macrocyclic compounds can indeed bring many excellent performances to the supramolecular chemistry systems.Hence,development of new types of macrocyclic hosts has served as important milestones in the field.As a new type of macrocyclic compounds,calix[4]pyrrole was first synthesized by Baeyer in 1886.But the exact structure of calix[4]pyrrole was first correctly characterized as a meso-octamethyl substituted tetrapyrrolic macrocycle by Chelintzev and Tronov in 1916,which can exist in four limiting conformations,namely,the so-called cone,partial cone,1,2-alternate,and 1,3-alternate conformations.These characteristics have also aroused great interests among scientists.Surprisingly,Sessler et al.found that calix[4]pyrrole has the ability to bind halide anions efficiently as the result of hydrogen bonding interactions involving the pyrrole NHs and the anions in 1996.In particular,complexation of an anion to calix[4]pyrrole via four hydrogen bonds drives conversion from the 1,3-alternate to the cone conformation.Subsequently,Gale revealed that calix[4]pyrrole and its derivatives can serve as hosts for neutral molecules which can accept pyrrole NH-anion hydrogen bonds.Based on the attractive framework of calix[4]pyrrole,it is found that the ?-pyrrolic carbon and meso-carbon atoms are relatively easy to modify and chemically functionalized.This is helpful to produce heteromultitopic ion pair receptors containing more than two cation binding sites and possessing right cavity volume.Meanwhile,this allows the interactions between receptors and ions to be manipulated on a higher level than can be achieved using simple ion receptors or heteroditopic ion pair receptors and has made these systems attractive for use in ion transport,recognition,and extraction.Spontaneous assembly through molecular recognition is an efficient way to build up complex superstructures.Calix[4]pyrrole derivatives have been proven to be important building blocks for supramolecular assembly due to its recognition ability to multitopic anions and ion pair receptors.It was reported that calix[4]pyrrole derivatives can bind with electron deficient nitroaromatic molecules with certain stoichiometry.In addition,Ballester et al.synthesized a series of water-soluble calix[4]pyrrole compounds via functionalization of hydrophilic groups,which are attractive candidates to achieve selective binding in an aqueous solution of N-Oxides having biological activity.The attractive characteristics of calix[4]pyrrole and our experience in fluorescence technique inspired us to make a hypothesis that reversible assembly and disassembly between typically designed calix[4]pyrrole derivatives and perylene bisimide diacid(PDA)via noncovalent interaction could show interesting behaviors.Formation of supramolecular assembly would probably promote disaggregation of PDA and result in systems with enhanced and observable fluorescence.On the basis of the hypothesis,we design two supramolecular self-assembled systems built up from calix[4]pyrrole derivatives and PDA,and explore their sensing behaviors.The dissertation mainly consists of the following two sections.In the first section,cholesterol-functionalized calix[4]pyrrole(CCP)was synthesized and used to construct a fluorescent supramolecular ensemble with the ammonia salt of a perylene bisimide derivative(PDA).It was found that formation and disruption of the supramolecular ensemble could be easily controlled by injecting and evaporating ammonia.Meanwhile,the reversible process is accompanied by remarkable color change in both absorbance and fluorescence.1H NMR studies revealed that the composition of the supramolecular ensemble is that two molecules of CCP combine one molecule of the ammonia salt of PDA.Additionally,the fluorescent supramolecular ensemble could act as dual-analyte-dependent chemoresponsive materials of electron-poor TNT and electron-rich phenol in solution state,and the two sensing processes are irreversible.Specifically,the fluorescence emission of the supramolecular ensemble in solution state is sensitive to the presence of TNT(DL<80 nM),but partially to dinitrotoluenes(DNTs)and nitrobenzene(NB)depending on the specific structure of them.Interestingly,it was found that phenol in the vapor state is also an efficient quencher of the fluorescence emission of the ensemble,and the sensing could be performed in a visualized manner.Therefore,a fluorescent film based on the supramolecular ensemble was fabricated,which could be used to detect phenol vapor with high sensitivity,fast response speed and full reversibility,and the relevant detection limit(DL)is lower than 1 ppb.Upon the basis of the findings,a fluorescent device based on the fluorescent sensing film was fabricated,and successfully used for monitoring "phenol leaking" with excellent performances.In the second section,we synthesized a new compound containing two calix[4]pyrrole units linked by terephthaloyl chloride(DPCP).It was found that DPCP could be used to construct a fluorescent supramolecular ensemble with PDA in the presence of DBU,and the binding stoichiometry of DPCP and PDA in the supramolecular ensemble is 2:1.Meanwhile,there are residues of calix[4]pyrrole units in the supramolecular ensemble.Hence,we proposed that combined the supramolecular ensemble PDA/(DPCP)2/DBU and treated PMMA plate via non-covalent interaction to prepare a multiple assembled sensing film.It was found that the sensing film is sensitive to phenol vapor.Although the sensitivity is slightly lower than the film in the first section,the fluorescence behaviors of the sensing film are improved in a great extent.This,in turn,is expected to provide a new approach for the construction of sensing film with excellent performance.