Stopper anthracene

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

In other studies, the above research group synthesised a number of related one-and two-station, photoactive [2]-rotaxanes incorporating either ferrocene or anthracene stoppers or a combination of each type. In these systems, the terminal stoppers associate with the exterior of the bis(4-4 -bipyridinium)cyclophane tetracation via 7U-stacking. Such proximity has obvious implications for the required rapid electron-transfer to a terminal (ferrocenyl) group in order to be competitive with the simple charge recombination process discussed previously. The relationship between the photoactivity, electron-transfer behaviour and concomitant configurational charges in the above systems has now been described in some detail. " ... 

Figure 8. Examples of pseudorotaxane components containing units capable of exhibiting specific properties, (a) A wire with an ammonium function and a photoactive anthracene as a stopper [17b] (b) a bipyridinium-type wire with a photo- and redox-active Ru(bpy)j + moiety [18] (c) a crown ether incorporating a binaphthyl unit [19] (d) a cyclophane containing a Re complex and two bi-pyridinium units (20. ...

In the assembly shown in Fig. 3 steam is passed into a 250-mL, round-bottomed flask through a section of 6-mm glass tubing fitted into a stillhead with a piece of 5-mm rubber tubing connected to a trap, which in turn is connected to the steam line. The trap serves two purposes it allows water, which is in the steam line, to be removed before it reaches the round-bottomed flask, and adjustment of the clamp on the hose at the bottom of the trap allows precise control of the steam flow. The stopper in the trap should be wired on, as shown, as a precaution. A bent adapter attached to a long condenser delivers the condensate into a 250-mL Erlenmeyer flask. Measure 50 mL of a 0.2% solution of anthracene in toluene into the 250-mL round-bottomed flask and add 100 mL of water. For an initial distillation to determine the boiling point and composition of the toluene-water azeotrope, fit the stillhead with a thermometer instead of the steam-inlet tube (see Fig. 5 in Chapter 5). Heat the mixture with a hot plate and sand bath or... 

If anthracene stoppers are attached, this pH driven locomotion of the CD rings becomes completely reversible and can be monitored in situ using fluorescence resonance energy transfer (FRET) of suitable fluorescent probes attached to the CD rings and to both ends of the polymer [269],... 

Figure 5. Some pseudorotaxane components containing units capable of exhibiting specific properties. The wirelike molecule 11H+, with an ammonium center and a photoactive anthracene unit as a stopper [40] the bipyridinium-containing wire 12 +, with a photo- and redox-active [Ru(bpy)3]2+ moiety [41] crown ether 13, incorporating a binaphthyl unit [42] cyclophane 14 +, which contains a [Ru(bpy)3]2+ complex and...

In a very recent work [117], the complex fluorescence behavior exhibited by a similar peptide-based [2]rotaxane bearing an anthracene unit as one of the stoppers has been interpreted in terms of a very fast (subnanosecond), short-amplitude translation of the macrocycle upon light excitation of the anthracene subunit. However, it seems that alternative explanations, such as the formation of intercomponent exciplexes [118], cannot be ruled out. 

Fluorescence spectroscopy was used also as a detection tool in case of a peptide based [2]rotaxane [72]. It was observed that in polar solvents like dimethyl sulfoxide (DMSO) fluorescence emission spectra were virtually same like those of the thread alone. Since fluorescence origins in this rotaxane from anthracene group, it was concluded that hydrogen bonds linking the macrocycle to the anthracene-based stopper were broken and the macrocycle resided on the alkyl side of the thread. When the solvent was hardly polar like 1,4-dioxane, the macrocycle rest bonded to the anthracene stopper and the spectrum broadened and red-shifted. By mean of time-resolved fluorescence spectroscopy, the authors demonstrated that it was... 

Anthracene groups are sufficiently large to prevent the dethreading of a-CD and /3-CD from an axle, and photoirradiation produces dimers. Consequently, poly(polyrotaxane)s and poly(catenane)s can be obtained by the photoirradiation of polyrotaxanes, with anthracene groups as stoppers. Recently, the present authors reported the preparation of poly(a-CD polyrotaxanes) by the photoirradiation of polyrotaxanes with 9-anthracene [87]. 

A multilevel fluorescence switch (Figure 12) was reported by Li, Zhu, and coworkers. A crown-ether-based macrocycle was bound mechanically onto a dumbbell possessing two different recognition sites a NH2 center and an amide unit. The molecular switch can be operated by changing the pH or by adding or removing Li" " or Zn ", which can be easily monitored by the different levels of the luminesce of the anthracene group in the stopper. 

In general, it becomes more difficult to prepare polyrotaxanes containing f -CD than a-CD, because the cavity of fi-CD is large so that it is hard to find suitable stopper groups to prevent their dethreading. Harada et al. [14] described an alternative approach for the one-pot preparation of /i-CD-based polyrotaxanes by making use of the photocyclodimerization of anthracene. 

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