Azobenzene (AB) and its derivatives are of great interest as molecular photoswitches because of the large-amplitude structural changes between their elongated (E) and more compact (Z) forms, the reversibility of their transformations, and their high photostabilities, which guarantee large numbers of switching cycles. The photochromic properties of AB are, however, far from ideal, because the S1(nπ*) electronic absorption bands of the E and Z isomers peak at practically the same wavelength (λ = 450 - 440 nm) and differ significantly only in their oscillator strengths.
We (re)discovered a "bridged azobenzene", 5,6-dihydrodibenzo[c,g][1,2]diazocine, which had not been investigated in detail as a photoswitch. Static UV/VIS and femtosecond transient absorption studies showed that this diazocine exhibits far superior photoswitching properties than plain AB.
The Z and E isomers of 5,6-dihydrodibenzo[c,g][1,2]diazocine.
Since its rediscovery by us, diazocine and diazocine derivatives have become favorite photoswitches in the CRC 677 "Function by Switching" at CAU Kiel. Current work in our group includes studies of diazocine derivatives, related bridged compounds predicted by theoretical work in the Hartke group and synthesized in the Herges group, and investigations of the photoswitching dynamics of diazocines embedded in PMMA polymers prepared in collaboration with the Staubitz group and the group of Walter Richtering and Felix Plamper at RWTH Aachen.
- R. Siewertsen, J. B. Schönborn, B. Hartke, F. Renth, F. Temps, "Superior Z - E and E - Z Photoswitching Dynamics of Dihydrodibenzodiazocine, a Bridged Azobenzene, by S1(nπ*) Excitation at λ = 387 and 490 nm", Phys. Chem. Chem. Phys.13, 1054 - 1063 (2011). DOI: 10.1039/C0CP01148G
- R. Siewertsen, H. Neumann, B. Buchheim-Stehn, R. Herges, C. Näther, F. Renth, F. Temps, "Highly Efficient Reversible Z - E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands", J. Am. Chem. Soc. 131, 15594 - 15595 (2009). DOI: 10.1021/ja906547d