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Photoisomerization in dendrimers by harvesting of low-energy photons

Nature volume 388, pages 454–456 (1997)Cite this article

Abstract

Infrared radiation can induce low-frequency molecular vibrations, but, with the exception of hydrogen-bond reorganization1,2,3, the excitation energy tends to be dissipated rapidly through molecular collisions rather than inducing photochemical changes. Here we show that in a macromolecular system that is designed to be insulated against collisional energy scattering, infrared absorption can excite photoisomerization by multiphoton intramolecular energy transfer. We have prepared highly branched dendrimers4,5,6 from aryl ethers with a photoisomerizable azobenzene core, in which infrared excitation of the aromatic units is apparently followed by a channelling of the absorbed energy to the core while the dendrimer matrix protects against collisional de-excitation. These findings suggest a strategy for harvesting low-energy photons to effect chemical transformations.

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Figure 1: Schematic representations of the isomerization of azobenzene (top left) and the structures of trans-LnAZO (n = 1, 3–5) and trans-mono-L6′AZO; here n represents the number of aromatic layers.
Figure 2: Effect of the number of aromatic layers (n) in LnAZO on: a, 1H NMR pulse relaxation times (T1) of trans-LnAZO (n = 1, 3–5) at 21 °C; b, first-order rate constants of the cis-to-trans isomerization of LnAZO (n = 1, 3–5) at 21 °C under infrared irradiation (kIR) relative to those of the thermal isomerization in the dark (kdark)
Figure 3: Isomerization profiles of L1AZO (a) and L5AZO (b) in infrared radiation (•) at 21 °C in comparison with the.
Figure 4: Dependence on the irradiation distance d of the first-order isomerization rate constant (kIR) of cis.

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Acknowledgements

We thank T. Kitamori for discussions, Y. Okamoto and E. Yashima for molecular modelling calculations, and JASCO Co. Ltd. for providing a model CT-25C infrared light monochromator. D.-L.J. thanks JSPS for a Young Scientist Fellowship.

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Authors and Affiliations

  1. Fields and Reactions, Precursory Research for Embryonic Science and Technology, Japan Science and Technology Corporation,

    Dong-Lin Jiang & Takuzo Aida

  2. Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, 113, Tokyo, Japan

    Dong-Lin Jiang & Takuzo Aida

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  1. Dong-Lin Jiang
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Correspondence to Takuzo Aida.

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Jiang, DL., Aida, T. Photoisomerization in dendrimers by harvesting of low-energy photons. Nature 388, 454–456 (1997). https://doi.org/10.1038/41290

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