Sulfonatocalix[8]arene as a potential reaction cavity: photo- and electro-active dicationic guests arrest conformational equilibrium

Kaliappan, Raja ; Ling, Yonghua ; Kaifer, Angel E. ; Ramamurthy, V. (2009) Sulfonatocalix[8]arene as a potential reaction cavity: photo- and electro-active dicationic guests arrest conformational equilibrium Langmuir, 25 (16). pp. 8982-8992. ISSN 0743-7463

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Official URL: http://pubs.acs.org/doi/abs/10.1021/la900659r

Related URL: http://dx.doi.org/10.1021/la900659r

Abstract

Smaller members of water-soluble sulfonated calixarenes have been extensively explored in the context of host-guest complexation, supramolecular chemistry, and potential sensors. However, larger members especially eight-membered calixarene (CA[8]) has received much less attention because of its floppy nature and tendency to exist as a mixture of conformational isomers. Our continued interest in identifying molecules with an internal cavity as reaction vessels has led us to examine the host-guest complexation of CA[8] with photoactive bispyridyl ethylenes. We find that 4,4'-bispyridyl ethylene and 3,3'-bispyridyl ethylene upon complexation to CA[8] arrest the conformational equilibrium and force the latter to adopt a single conformation in solution. During complexation, bispyridyl ethylenes are protonated by the sulfonic acid groups of CA[8]. The host-guest complex is stabilized via an electrostatic interaction between the cationic bispyridyl ethylenes and anionic sulfonated calix[8]arene, and we propose the complex to have an inverted capsular structure. This model is also consistent with the electrochemical behavior of 4,4'-dimethylviologen included within CA[8]. Rigidification of bispyridyl ethylenes by the host has a consequence on the excited-state chemistry of the former. Generally, prevalent geometric isomerization of bispyridyl ethylenes are prevented by CA[8] upon complexation.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:55880
Deposited On:19 Aug 2011 07:51
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