Dimeric anthracene-linked

Liu HY, Abdalmuhdi I, Chang CK, Anson FC. 1985. Catalysis of the electroreduction of dioxygen and hydrogen peroxide by an anthracene-linked dimeric cobalt porphyrin. J Phys Chem 89 665. 

With these anthracene-linked dimeric cinchona-PTCs, the Najera group investigated the counterion effect in asymmetric alkylation of 1 by exchanging the classical chloride or bromide anion with tetrafluoroborate (BF4 ) or hexafluorophosphate (PF6-) anions (Scheme 4.10) [17]. They anticipated that both tetrafluoroborate and hexafluorophosphate could form less-tight ionic pairs than chloride or bromide, thus allowing a more easy and rapid complexation of the chiral ammonium cation with the enolate of 1, and therefore driving to a higher enantioselectivity. However, when... 

These anthracene-linked dimeric PTCs (42-53) were also employed in the Michael addition reaction of 1 by the Najera group (Scheme 4.11) [18], Depending on the Michael acceptor and the nature of the counter anion part of the ammonium cation in PTC, a variation of both chemical yield and stereoselectivity was observed. 

Photoresponsive systems are seen ubiquitously in nature, and light is intimately associated with the subsequent life processes. In these systems, a photoantenna to capture a photon is neatly combined with a functional group to mediate some subsequent events. Important is the fact that these events are frequently linked with photoinduced structural changes in the photoantennae. This suggests that chemical substances that exhibit photoinduced structural changes may serve as potential candidates for the photoantennae. To date, such photochemical reactions as E/Z isomerism of azobenzenes, dimerization of anthracenes, spiropyran-merocyanine interconversion, and others have been exploited in practical photoantennae. It may be expected that if one of these photoantennae were adroitly combined with a crown ether, it would then be possible to control many crown ether family physical and chemical functions by means of an ON/OFF photoswitch. This is the basic concept underlying the designing of photoresponsive crown ethers. We believe that this is one of the earliest examples of molecular machines . 

In this system, however, intermolecular dimerization may take place competitively with intramolecular dimerization. To rule out this possibility, compound 5, in which two anthracenes are linked by two polyether chains, was synthesized.171 It was found that intramolecular photodimerization proceeds rapidly in the presence of Na+ as the template metal cation. Compound 6 was also synthesized.181 Although this compound has not been applied in a photoswitch system, it displays a remarkable fluorescence change upon binding with RbC104 or H3N+(CH2)7NHj.[81 Yama-shita et al.[9] also synthesized 7, in which intermolecular photodimerization of anthracene is completely suppressed. The photochemically produced cyclic form 8 displayed excellent Na+ selectivity. 

Much information about the detailed mechanism of anthracene dimerization was gained in the study of intramolecular photoreactions of linked anthracenes such as a,(d-bis(9-anthryl)aikanes (66). It was shown that luminescence and cycloaddition are competing pathways for the deactivation of excimers. In compounds with sterically demanding substituents R and R that impair the cycloaddition reaction, the radiative deactivation is enhanced (H.-D. Becker, 1982). 

Anthranoid laxative plants The anthranoid-containing plants are essentially similar in their mode of action. In this group the active substances are a group of polynuclear or tricyclic hydrocarbon derivatives based on anthracene. Various oxidised and reduced forms constitute the aglycones of a variety of C and O glycosides. The fully oxidised form is the anthraquinone form, with the partially reduced form represented by the an-throne nucleus. Dimeric forms whereby two anthracene nuclei are chemically linked to... 

Normal head-to-head 4n-i-47c photodimerisation has been found for the series of anthracenes (244)-(251) which are all linked by a three carbon chain. The dimers have structures (252)-(259), respectively, and their quantum yields of formation have been determined and are... 

Another unique dimeric system was first reported by Naruta and Maruyama in 1991 (443-445). In this system, two MnIU-porphyrin molecules are linked by an anthracene spacer instead of the o-phenyl-ene spacer seen in Fig. 75 (discussed later). Their studies showed this... 

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