| Abstract
| - We report on the first direct atomic-level photodiffraction evidence for domain formation by doping withcharge photocarriers of the stable organic radical TTTA (1,3,5-trithia-2,4,6-triazapentalenyl), which exhibitsunusually wide thermal hysteresis of the paramagnetic-to-diamagnetic phase transition around ambienttemperature. A setup for steady-state powder photodiffraction was developed for the purpose, composed ofa second harmonic pulsed visible pump (532 nm) coupled with a powder diffractometer using monochromaticsynchrotron X-ray radiation as the probe. The refined structures of the photoinduced phase and the high-temperature phase are structurally identical. The result supports the model according to which photoexcitationcauses suppression of the spin-Peierls instability and separation of the radical dimers, resulting in a structurethat is essentially identical with the unperturbed high-temperature phase.
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