Dynamic Pseudo[1]Rotaxane And Controllable Pseudo[2]Rotaxane Based On Pillar[5] Arene

Supramolecular chemistry has become an intersectional frontier field where chemistry, physics, materials science, and life science are combined together. One of the goals of the supramolecular chemistry is to build complex, highly ordered, and specific functional molecular machines, which can be applied for the translation of information, storage, processing, and scheduling, like most of molecular machines found in biological nature. Pseudorotaxanes, as the cornerstone of molecular machine, have attracted considerable interest in the fields of supramolecular chemistry and materials chemistry in the past decades because of not only their special topological structures but also their mechanical, biological, and electronic functions can be achieved with their self-assemblies.Pillar[5]arenas, a new class of macrocycles for supramolecular chemistry, after being functionalized, has proved to be excellent hosts for alkyl chain derivatives, viologen cations, (bis)imidazolium cations, ammonium cations, dicarboxylates, L-lysine, L-arginine and neutral bis(imidazole) derivatives, neutral guest. In the last seven years since its first discovery, it has been widely applied in the construction of rotaxane as the basis of molecule recognition, rotaxanes, supramolecular polymers, molecular springs, artificial transmembrane channels, vesicles, and MOFs (metal-organic frameworks). Although the intensity of the host-guest interactions, hydrogen bonding et al. are weak, under the cooperative effect of several orthogonal interactions, small molecules could assemble into more stable architectures. This dissertation focus on the synthesis and applications of various guest molecular to match functional pillar[5]arene and consists of two parts of research work:Part 1, we reported the preparation of an unconventional pseudo[1]rotaxane 2-1conf1, which could be isolated from its non-inclusion analogue 2-1u temporarily and exhibited spontaneous but slow isomerization in DMSO. HR-ESI-MS, various concentration 1H NMR measurements and 2D ROESY NMR proved the intramolecular self-inclusion structure of 2-lconn. Different from previous pseudo[1]rotaxanes, it could be seen three constructions of 2-1u,2-lconn and 2-lconf2 from the NMR spectra directly that could transform each other even in high polar solvent. The construction difference between 2-lconn and 2-lconf2 is in the position of the binding site, only the formation of 2-1 conf1 was induced by H-bond of amide group and urea group. The addition of fluoride ion could accelerate the transformation from 2-lconn to 2-lconf2 by destroying the H-bond of urea group. The reason that self-inclusion structure 2-lconn and 2-lconf2 could remain stable in polar solvent was due to two factors:(1) Urea moiety. When Urea moiety stay in appropriate position, the compound could form stable intramolecular hydrogen bond to stabilize self-inclusion structure. The Lengthening the distance between the urea moiety and the P5 cavity or eliminating the urea moiety will decrease its stability in polar solvent. (2) Stopper size. When some small moieties such as amino or acetyl group was used to replace N-Boc stopper, the self-inclusion structure would be formed in polar solvent. And replacing the N-Boc stopper with bulky 3,5-di-tert-butylbezene moiety only lead to form interlocked [1]rotaxane. From these experimental facts we reach a conclusion that the suitable stopper size and urea group should make the way to form this special pseudo[1]rotaxane in high polar solvent.Part 2, we reported a series of neutral guests and tried to combine them with per-ethylated pillar[5]arene. The neutral guest consist of end functional group, link group and tetramethylene bone. Fortunately, we got G1 which has the structure of dibenzyl tetramethylene bis-carbamate could form pseudo[2]rotaxane with EtP[5] A. The reason that pseudo[2]rotaxanes could remain stablet was due to two factors:(1) End functional group. When small moieties such as n-propyl group was used to replace, the guest could not stay in the cavity of EtP[5]A, and replacing the phenyl group with t-butyl group lead to guest could not through the cavity. (2) Link group. The carbamate could form more hydrogen bond with the alkoxy of pillararene than urea group. For the neutral guest, hydrogen bond is the most important factor to form stable pseudorotaxanes. As is well known, o-nitrobenzyloxycarbonyl group, was used as a highly sensitive photocleavage group, whose structure is very similar as G1. Base on the above research, one or two NO2 groups were introduced into the benzyl group of G1 to achieve two new neutral guests, symmetrical G6 and unsymmetrical G7, which could possibly complex with EtP[5]A as G1 did. But the size of the two o-nitrophenyl end-functional groups of G6 was too bigger to thread into the cavity of EtP[5]A. However, in G7 case where only one NO2 group was introduced into one of benzyl group to obtain unsymmetrical guest G7, the pseudo[2]rotaxane could be well constructed from EtP[5]A and G7. Meanwhile, the UV-responsiveness of G7cEtP[5]A was tested. After exposed in 365 nm ultraviolet light for 1.5 hours, the solution colour dramatically changed into yellow and plenty of precipitates from the chloroform-d were observed at the same time.