Studies of a photochromic model system using NMR with ex-situ and in-situ irradiation devices

• Published in: Magnetic resonance in chemistry 2016-06, Vol.54 (6), p.485-491
• Main Authors: Wolff, Christiane, Kind, Jonas, Schenderlein, Helge, Bartling, Hanna, Feldmeier, Christian, Gschwind, Ruth M., Biesalski, Markus, Thiele, Christina M.
• Format: Article
• Language: English
• Subjects: Devices; Illumination; illumination device; Irradiation; LED; Mathematical models; merocyanine; NMR; Nuclear magnetic resonance; photochromism; Spectra; spiropyran; Spiropyrans; Two dimensional; UV/VIS
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.4403

The switching behavior of a photochromic model system was investigated in detail via NMR spectroscopy in order to improve understanding of the compound itself and to provide ways to obtain insights into composition trends of a photo switchable (polymeric) material containing spiropyran/merocyanine units. In addition to the classical irradiation performed outside the magnet (ex‐situ), a device for irradiation inside the NMR spectrometer (in‐situ) was tested. Both setups are introduced, their advantages and disadvantages as well as their limits are described and the setup for future investigations of photochromic materials is suggested. The influence of different sample concentrations, irradiation procedures, and light intensities on the model system was examined as well as the dependence on solvent, temperature, and irradiation wavelengths. Using the recently published LED illumination device, it was even possible to record two‐dimensional spectra on this model system with rather short half‐life (7 min in DMSO). This way 13C chemical shifts of the merocyanine form were obtained, which were unknown before. Copyright © 2016 John Wiley & Sons, Ltd. The photochemical equilibrium of a spiropyran/merocyanine system was investigated NMRspectroscopically. The equilibrium between the stable spiropyran and the short lived merocyanine form was shifted by irradiation ex‐situ and in‐situ. Using in‐situ illumination inside the NMRspectrometer using a LED‐illumination device also allowed the observation of the formation of merocyanine. 2D spectra could be recorded of the merocyanine form, such that almost completeassignment of the merocyanine form was possible.