Dynamic internal cavities of dendrimers as constrained media. A study of photochemical isomerizations of stilbene and azobenzene using poly(alkyl aryl ether) dendrimers

Natarajan, Baskar ; Gupta, Shipra ; Jayaraj, Nithyanandhan ; Ramamurthy, V. ; Jayaraman, Narayanaswamy (2012) Dynamic internal cavities of dendrimers as constrained media. A study of photochemical isomerizations of stilbene and azobenzene using poly(alkyl aryl ether) dendrimers Journal of Organic Chemistry, 77 (5). pp. 2219-2224. ISSN 0022-3263

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jo2024027

Related URL: http://dx.doi.org/10.1021/jo2024027

Abstract

Dendritic microenvironments defined by dynamic internal cavities of a dendrimer were probed through geometric isomerization of stilbene and azobenzene. A third-generation poly(alkyl aryl ether) dendrimer with hydrophilic exterior and hydrophobic interior was used as a reaction cavity in aqueous medium. The dynamic inner cavity sizes were varied by utilizing alkyl linkers that connect the branch junctures from ethyl to n-pentyl moiety (C2G3-C5G3). Dendrimers constituted with n-pentyl linker were found to afford higher solubilitiesof stilbene and azobenzene. Direct irradiation of trans-stilbene showed that C5G3 and C4G3 dendrimers afforded considerable phenanthrene formation, in addition to cis-stilbene, whereas C3G3 and C2G3 gave only cis-stilbene. An electron-transfer sensitized trans-cis isomerization, using cresyl violet perchlorate as the sensitizer, also led to similar results. Thermal isomerization of cis-azobenzene to trans-azobenzene within dendritic microenvironments revealed that the activation energy of the cis- to trans-isomer was increasing in the series C5G3 < C4G3 < C3G3 < C2G3. With the change in the alkyl linker from C5 to C2, significant changes in the activation parameters were observed.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:91586
Deposited On:22 May 2012 12:40
Last Modified:22 May 2012 12:40

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