Study On The Host-guest Interaction And Modification Of A New Type Of Macrocyclic Compound Multifarenes

The emergence of novel macrocyclic compounds has promoted the development of supramolecular chemistry.Multifarene as a new class of host macrocycles,which research is still in its infancy,and it is necessary to conduct in-depth investigation and functional development of its supramolecular chemistry.The host-guest interactions of multifarenes with neutral organic molecules and the functionalization of multifarene[2,2]and their molecular recognition properties have been investigated from the supramolecular chemistry of this new class macrocyclic compound in this work.Host-guest interactions of multifarenes 1-3 with naphthylamines and naphthols4-7 were investigated by fluorescence emission spectroscopy,¹H NMR spectrometry and molecular simulation.Decreased fluorescence emission of the guests upon addition of increasing amounts of multifarene hosts confirmed the formation of host-guest complexes in a ratio of 1:1.Non-linear curve fitting showed moderate association constants of between?5.2±0.7?×10³ and?2.3±0.6?×10⁴ L/mol.The stabilities of the complexes were dependent upon both the ring size of the host and the structure of the guest.¹H NMR spectra indicated that the interactions involved hydrogen bonds between the amine or hydroxyl groups of the guests and the hydroxyl groups of the multifarenes.Molecular simulations were performed to provide the microcosmic structures of the interaction complexes.Two fluorescent chemosensors 11-12 based on an anthracene or pyrene-functionalized triazole-linked multifarene[2,2]were successfully synthesized and investigated with regard to recognition of metal ions using fluorescence spectroscopy,¹H NMR titration,and IR spectroscopy.The proposed sensor exhibited desirable properties for potential fluorescence enhancement chemosensor applications,including selective affinity and high Zn²⁺and Cd²⁺detection limits compared with other metal ions.Quantum chemical calculations described the synthesized chemosensor's static structure and its coordination to Zn²⁺and Cd²⁺.Frontier molecular orbital distribution and energy changes suggested a possible mechanism for increased receptor fluorescence intensity with Zn²⁺and Cd²⁺addition.Two fluorescent chemosensors 13-14 based on the multifarene[2,2]framework disubstituted with pyrene or anthracene moieties were successfully synthesized.These macrocyclic sensors exhibited high affinity and selectivity toward Ag⁺over other metal ions,with ratiometric or enhanced response of their fluorescence emissions depending upon the substituent species for coordination to Ag⁺,and an unexpected response to a concentration threshold of the metal cations was discovered.The experimental evidences of fluorescence spectra,¹H NMR titration,IR spectra,and high-resolution mass spectra suggested the coordination behaviors of the sensors with Ag⁺,that is,the 1:1 complexes were formed with moderate association constants of about 10⁵ L/mol,and the sulfur atoms on macrocyclic ligand should affinite to the metal cations.Quantum chemical calculations described the synthesized chemosensor's static structure and its coordination to Ag⁺.Frontier molecular orbital distribution and energy changes explained the ratiometry and enhancement of fluorescence response of the macrocyclic receptors upon coordination to Ag⁺.Substituted multifarene[2,2]11-14 recognition of nitrophenols were investigated by fluorescence emission spectroscopy,UV-vis absorption spectrometry and ¹H NMR spectrometry.11 and 13 can efficiently and rapidly detect 2,4,6-trinitrophenol?TNP?,as confirmed by the fluorescence titration experiments.The selective detection of TNP in the presence of other competing phenolic compounds with the detection limit of¹0^-8 mol/L.The extraordinarily selective fluorescence quenching is assigned to the presence of energy and charge transfer processes.¹H NMR titration analysis revealed the actual binding position of sensors with TNP.