Work Group Prof. Dr. F. Temps

JACS communication hot of the press (published on the web: 14 October 2009)

14 October 2009: 


Highly Efficient Reversible ZE Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands

Ron Siewertsen, Hendrikje Neumann, Bengt Buchheim-Stehn, Rainer Herges, Christian Näther, Falk Renth and Friedrich Temps

J. Am. Chem. Soc. 131, 15594 - 15595 (2009),  DOI: 10.1021/ja906547d  




The reversible ZE photoswitching properties of the (Z) and (E) isomers of the severely constrained bridged azobenzene derivative 5,6-dihydrodibenzo[c,g][1,2]diazocine (1) were investigated quantitatively by UV/vis absorption spectroscopy in solution in n-hexane. In contrast to normal azobenzene (AB), 1 has well separated S1(nπ*) absorption bands, peaking at λZ = 404 nm and λE = 490 nm. Using light at λ = 385 nm, it was found that 1Z can be switched to 1Ewith very high efficiency, Γ = 92 ± 3%. Conversely, 1E can be switched back to 1Z using light at λ = 520 nm with ∼100% yield. The measured quantum yields are ΦZ→E = 72 ± 4% and ΦE→Z = 50 ± 10%. The thermal lifetime of the (E) isomer is 4.5 ± 0.1 h at 28.5 °C. The observed photochromic and photoswitching properties of 1 are much more favorable than those for normal AB, making our title compound a promising candidate for interesting applications as a molecular photoswitch especially at low temperatures. The severe constraints by the ethylenic bridge apparently do not hinder but favor the ZE photoisomerization reactions.

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