MS36-P26 Unexpected long-lived photogenerated High-Spin phase investigated by X-ray diffraction.Spin crossover compounds are interesting photoswitchable materials, with possible applications in sensing or memory devices. At low temperature the Low-Spin state can be excited into the photoexcited High-Spin state through the Light-Induced Excited Spin-State Trapping (LIESST) effect. The relaxation time is however usually short at higher temperatures.
The spin-crossover compound [Fe(n-Bu-im)3(tren)](PF6)21 shows an unusual long relaxation time at 80K of 20 hours after Light-Induced Excited Spin-State Trapping when irradiated at 80 K. This is more than 40 times longer than the 80K relaxation time when irradiated at 10 K. To explain this unusual behavior single crystal structures were determined after irradiation at low temperature and at 80K. The structures of the two excited High-Spin states differ in the configuration of the side alkyl chains of the compound. Using synchrotron radiation, the long relaxation at 80K could be monitored by single-crystal X-ray diffraction. We showed that the rearrangements of the alkyl chains, which undergo order-disorder transitions, are responsible for the unexpected long relaxation time.
These results highlight the importance of structural studies to better understand and control the LIESST photoexcited states. Multimetastability can be exploited to tune the properties of the system.
1 Seredyuk M., Muñoz M.C., Castro M., Romero-Morcillo T., Gaspar A.B. & Real J.A.(2013). Chemistry - A European Journal. 19 6591-6596Keywords: Photoswitcable materials, Spin Crossover, structure