Naphthalene-based crowns

Recently, Brown, Muenchausen and Sousa " have reported the preparation of an interesting group of naphthalene-based crowns which are characterized by these authors... 

In the UV spectral range complexation with 18-crown-6 causes a hypsochromic shift of the band with the longest wavelength in various solvents (Bartsch et al., 1976 Hashida and Matsui 1980). Gokel and Cram (1973) reported that complexation with binaphtho-20-crown-6 (11.2) produces a yellow to red color. This phenomenon is very likely to be due to a charge-transfer band between a naphthalene ring as donor (7i-base) and the arenediazonium ion as acceptor (7i-acid). 

The applicability of cesium fluoride for the synthesis of smaller crown ether rings such as benzo[12]crown-4 (35) was investigated by Bartsch et al. [45]. The result of this study was that the 12-membered crown ether 35 and its naphthalene analogue 36 can be obtained from the aromatic diols 33 and the tosylate 34 with the base cesium fluoride in yields of 29 and 25 %, respectively. This means a significant increase in the 4% yield of benzo[12]crown-4 (35) reported by Pedersen, who started with sodium phenolate [38]. 

The base is activated with 18-crown-6 Sodium naphthalene radical anion... 

The first concept to be considered is cation displacement of a complexed quencher of fluorescence. Scheme I illustrates the concq>t. To be operable the scheme requires a quencher that is complexed by a crown ether, a metal ion of interest that is not a quencher but is complexed effectively, and a crown ether ring that orients the complexed quencher so it will effectively quench the chromophore fluorescence. Scheme II shows a relatively simple crown ether system that we hoped would fulfill these requirements(22,2i). The l,5-naphtho-22-crown-6 compound was selected because of the ability of its crown ether band to hold a quencher against the face of the pi system of the naphthalene chromophore. The heavy atom ion Cs+ was selected as a quencher based on its propensity to increase inter-system crossing from the fluorescent Sj state to the nonfluorescent T state(i,2). It was likely, based on previous results(2), that potassium ion would be complexed by the crown, but not quench naphthalene fluorescence appreciably. 

Later, Stoddart et al. reported a nondegenerate molecular switch (Figure 15) driven by the change in the solvent polarity based on a [2]catenane comprising a cyclophane CBPQT + interlocked with a crown ether, which has a benzene unit and a naphthalene unit. The conformation of the [2]catenane can be changed due to the different interaction intensities between the cyclophane and the crown ether in polar and nonpolar solvents. 

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