Macrocycles bithiophene

The sensor covalently joined a bithiophene unit with a crown ether macrocycle as the monomeric unit for polymerization (Scheme 1). The spatial distribution of oxygen coordination sites around a metal ion causes planarization of the backbone in the bithiophene, eliciting a red-shift upon metal coordination. They expanded upon this bithiophene structure by replacing the crown ether macrocycle with a calixarene-based ion receptor, and worked with both a monomeric model and a polymeric version to compare ion-binding specificity and behavior [13]. The monomer exhibited less specificity for Na+ than the polymer. However, with the gradual addition of Na+, the monomer underwent a steady blue shift in fluorescence emission whereas the polymer appeared to reach a critical concentration where the spectra rapidly transitioned to a shorter wavelength. Scheme 2 illustrates the proposed explanation for blue shift with increasing ion concentration. 

Using each of the 2 + 2 synthetic pathways discussed above, Broadhurst, et al. also attempted to prepare bithiophene-containing corroles (cf. Schemes 2.1.8 and 2.1.9). However, in no case could any corrole-like products be obtained. This failure likely reflects the increased steric bulk of the sulfur atoms these presumably hinder effective macrocyclization. 

This macrocycle was first reported by Merz and Neidlein in 1993. It was isolated in 2.9% yield as a trimeric by-product from the reductive McMurry-type self-coupling of 2,5-diformyl bithiophene 7.89 (Scheme 7.7.8), a reaction that was originally intended to produce the tetrathiaporphycenogen 7.91 (see Chapter 3). ... 

Swager and coworkers synthesized receptor polymers 102 and 103 [209,210]. The polymers were prepared by copolymerization of 2,5-dibromo-3-decylthiophene or 3,3 -bis(methoxyethoxy)-2,2 -bithiophene with the organozinc derivative of the macrocyclic 3,3 -dialkoxy-2,2 -bithiophene by palladium-catalyzed cross-coupling. Cyclic voltammetry and in situ conductivity measurements on polymer films have evidenced the complexation of paraquat derivatives. However, the complexation between polymer films and acceptors can lead to opposite shifts of oxidation potential of the polymer due to the interplay of donor-acceptor interaction and conformational changes of the polymer. 

In an effort to overcome steric interactions due to -substituents in cyclotetra(2,3-thienylene)s 4.6 (see above), Marsella et al. synthesized expanded thiophene-fused didehydro [12]annulene 4.32, which incorporated two additional ethynylene groups between the -positions of the cycUc stmcture (Scheme 1.44) [408]. Regiospeciflc halogenation of a 2,2 -bithiophene and Sonogashira-type cross-coupling with the ethynylated counter part were key elements of the synthetic strategy, which was also used to prepare a further extended macrocycle 4.33 (Chart 1.54), profiting from quadrupolar interactions of the central phenylene units [409]. 

The same authors extended the structural variety of thiophene-based macrocycles by synthesizing [24]annulene 4.53 in which two 2,2 -bithiophene units are connected via butatriene groups (Chart 1.56). The macrocycle showed clear paratropicity (antiaromaticity) whereas the dianion, a 26K-electron system which is obtained by alkali reduction, was strongly diatropic (aromatic) [421]. 

Other polyrotaxanes containing a thiophene-based conjugated backbone have been synthesized from the Cu(I)- or Zn(II)-driven assembly between a macrocyclic phenanthroline and a bithiophene-substituted phenanthroline [322] or bipyridine [323, 324]. Swager and co-workers have demonstrated that the contribution of the metal ion to the electronic properties of the polyrotaxane was possible when more electron-rich 3,4-(ethylenedioxy)thio-phene groups were used in place of thiophenes in the polymer backbone [324]. So a 10 -10 -fold increase in the polymer s conductivity was observed after poly(24) was treated with Cu(II) solution. This result was ascribed to the oxidation of the poly(24) backbone by Cu " " ions to generate poly(24,Cu) with charge carriers in the polymer backbone. 

Rotaxane polymers can also be deemed as polyrotaxanes or pseudopolyro-taxanes, because they have the common structural characteristics that is, many macrocycles reside on a polymer chain. However, unlike polyrotaxanes or polypseudorotaxanes, which are synthesized from the slipping of macrocycles into a polymer chain, rotaxane polymers are synthesized from the polymerization of rotaxane (or pseudorotaxane) monomer, and monomer unit on the polymer chain has one macrocycle. Harada [16] reported the preparation of a rotaxane polymer based on the homopolymerization of bithiophene (2T) pseudorotaxane. Bithiophene formed hrst inclusion compound a-CD-2T with a-CD, and then the polymerizations of a-CD-2T in water using EeCls as an oxidative initiator after centrifugation, the resulting powder was washed with water and THE to remove unreacted monomer and the corresponding rotaxane polymer was found as deep purple powder. Earcas et al. [17] developed a novel aromatic polyazomethine polymer with rotaxane architecture by the copolymerization of a diformylcarbazole derivative with a benzenediamine pseudorotaxane in DME. 

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