Photoinduced diamagnetic to paramagnetic phase transition in organic radical crystals studied by microscopic IR measurements

Photoinduced magnetic phase transition in an organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystal has been studied by microscopic IR measurements. Both photoexcitations of the charge-transfer and intramolecular π-π transition bands induce a low-temperature diamagnetic to high-temperature paramagnetic phase transition but with different threshold photon densities. The behavior of the photoinduced magnetic phase transition in TTTA is discussed in comparison with previous results measured by the photoinduced Raman and ESR measurements.