Properties From Host-guest Interactions Of Cucurbit[n]uril With Linear Fluorescent Pyridium Derivatives

In supramolecular chemistry,cucurbit[n]urils(Q[n]s or CB[n]s)are a classical macrocyclic host with rigid cavity.Generally,the complex of Q[n]s with fluorophores can significantly modify the optical properties of guest.For example,Q[8] host,a large homologue of the Q[n] family,is unique due to its ability bind two guests such as fuorophores in its cavity,and lead to pronounced fluorescence changes.In this thesis,the host-guest interactions between Q[7]/Q[8] and a series of linear fluorescent pyridium derivetives were studied.The main contents include the following aspects:1.The pseudorotaxane process between Q[7] and linear pyridium fluorescent molecules with different alkyl chain lengths was monitored by fluorescence method.A series of linear ?-conjugated water-soluble cationic fluorescent pyridium derivetives with electronic acceptor-donor-acceptor(A-D-A)properties have been synthesized.The results of Q[7]-based host-guest interactions suggests that a dynamic sequence tunable from [2]pseudorotaxane to [4]pseudorotaxane and accompanied by a distinct smart enhancement of the fluorescence signal is elicited.Further studies indicated that the length of terminal aliphatic-chain play a crucial role in controlling of the supramolecular assemblies.In addition,the hydrophobic cavity and carbonyl-fringed portals of the Q[7] hosts are beneficial for switching of the fluorescence emissions of the guests by different binding fashions.2.The pseudorotaxane process between Q[8] and linear pyridium fluorescent molecules with different alkyl chain lengths and aromatic parents was monitored by fluorescence method.In this chapter,a series of dynamic 2:1,2:2,2:3,and 1:2 assemblies(guest/Q[8])were formed.Most importantly,those different host-guest binding models can be distinguished by real-time in situ monitoring or naked eye observation.In additional,fluorescence lifetime was exploited to help characterize the assemblies fashions of Q[8] with the guests.For example,the fluorescence lifetime changes were fully in line with the host-guest assembly modes confirmed by the fluorescence and NMR spectra,suggesting that fluorescence decay times may have potential in the characterization of Q[8]-chromophore system binding modes.Further studies indicated that those different models can be transformed into each other.Based on this principle,a fluorescent probe for detecting spermine and spermidine was designed.3.The pseudorotaxane process between Q[8] and curved pyridium fluorescent molecules with different alkyl chain lengths and aromatic parents was monitored by fluorescence method.Following the previously studies,we found that the assembly fashions of Q[8] with guests can be controlled by the steric groups such as methyl moiety on the ?-conjugated phenyl parent.In this chapter,we found that when larger steric groups were appended to the ?-conjugated parent or curved shape on the ?-conjugated aromatic moieties,the shutting motion of Q[8] on the guest can be inhibited.Experiment results suggested that linear supramolecular polymers with a molar ratio of 1:1(guest/Q[8])were formed.Similarly,the dynamic host-guest assembly also can be monitored in real-time by fluorescence.