Excited-state dynamics of TTTA studied by femtosecond luminescence spectroscopy

The excited-state dynamics in photoinduced phase transition material, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), was investigated by using femtosecond luminescence spectroscopy. The luminescence in low- and high- temperature phases was measured between 1.42 and 1.2 eV.Only in the low-temperature phase, we observed a luminescence, which has the decay time constant of 1.6 ps in the entire energy range. This decay time constant suggests the existence of a large non-radiative relaxation path in the low-temperature phase. It was found that the luminescence was depolarized in the Stokes region and the luminescence intensity does not depend on the polarization of the excitation light. This result suggests that the energy transfer between CT excited states with different orientations is large.