Photoinduced magnetic phase transition in an organic radical 1,3,5-trithia-2,4,6-triazapentalenyl crystal at room temperature

Photoinduced magnetic phase transition in an organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystal was investigated at room temperature through photoinduced ESR and Raman scattering measurements. We found that the photoexcitation of the charge-transfer band induces a low-temperature diamagnetic to high-temperature paramagnetic phase transition with a clear threshold photon density of ∼1.0 × 1021/cm3, while that of the intramolecular π–π transition band induces a phase transition without a clear threshold photon density. The mechanism of the photoinduced magnetic phase transition in TTTA is discussed in comparison with that of the photoinduced ionic-to-neutral phase transition in TTF-CA.