Photoinduced Trans‐to‐cis Phase Transition of Polycrystalline Azobenzene at Low Irradiance Occurs in the Solid State. Issue 18 (11th August 2017)

• Record Type: Journal Article
• Authors: Bhattacharjee, Ujjal; Freppon, Daniel; Men, Long; Vela, Javier; Smith, Emily A.; Petrich, Jacob W.
• Is Part Of: Chemphyschem. Volume 18:Issue 18(2017)
• Page Start: 2526
• Page End: 2532
• Publication Date: 2017-08-11
• Subjects: azobenzene -- isomerization -- phase change -- photochemistry -- trans-to-cis isomerization; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201700580
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The ability to produce large‐scale, reversible structural changes in a variety of materials by photoexcitation of a wide variety of azobenzene derivatives has been recognized for almost two decades. Because photoexcitation of trans ‐azobenzene produces the cis ‐isomer in solution, it has generally been inferred that the macroscopic structural changes occurring in materials are also initiated by a similar large‐amplitude trans ‐to‐ cis isomerization. This work provides the first demonstration that a trans ‐to‐ cis photoisomerization occurs in polycrystalline azobenzene, and is consistent with the previously hypothesized nature of the trigger in the photoactuated mechanisms of the materials in question. It is also demonstrated that under low irradiance, trans ‐to‐ cis isomerization occurs in the solid (not via a pre‐melted phase); and the presence of the cis ‐isomer thus lowers the melting point of the sample, providing a liquid phase. A variety of experimental techniques were employed, including X‐ray diffraction measurements of polycrystalline azobenzene during exposure to laser irradiation and fluorescence measurements of the solid sample. A practical consequence of this work is that it establishes trans ‐azobenzene as an easily obtainable and well‐defined control for monitoring photoinduced structural changes in X‐ray diffraction experiments, using easily accessible laser wavelengths. Abstract : Photons for change ! We demonstrate trans‐to‐cis photoisomerization of azobenzene in the solid state at low irradiance by using X‐ray diffraction and fluorescence measurements. Our findings establish trans‐azobenzene as an easily obtainable and well‐defined control for monitoring photoinduced structural changes in X‐ray diffraction experiments.