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

Baskar Natarajan, Shipra Gupta, Nithyanandhan Jayaraj, V. Ramamurthy, Narayanaswamy Jayaraman

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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 (C 2G3-C 5G3). Dendrimers constituted with n-pentyl linker were found to afford higher solubilitiesof stilbene and azobenzene. Direct irradiation of trans-stilbene showed that C 5G3 and C 4G3 dendrimers afforded considerable phenanthrene formation, in addition to cis-stilbene, whereas C 3G3 and C 2G3 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 C 5G3 < C 4G3 <C 3G3 <C 2G3. With the change in the alkyl linker from C 5 to C 2, significant changes in the activation parameters were observed.

Original languageEnglish (US)
Pages (from-to)2219-2224
Number of pages6
JournalJournal of Organic Chemistry
Issue number5
StatePublished - Mar 2 2012


ASJC Scopus subject areas

  • Organic Chemistry

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