Solvent 𝜆𝜆 q-ax. (nm) 𝜏𝜏 q-ax. (ns) 𝜆𝜆 q-eq. (nm) 𝜏𝜏 q-eq. promt (ns) 𝜏𝜏 q-eq. 𝑑𝑑𝑒𝑒𝑑𝑑𝑎𝑎𝑑𝑑𝑒𝑒𝑑𝑑 (ns) Our proposed model based on these results is shown in Figure . In both the solvents, UV irradiation excites both q-ax. and q-eq. to their high excited states (Sn). In toluene, which has the low permittivity solvent (ε =2.38), there are three relaxation processes from Sn in q-ax.: fluorescence with 422 nm, structural change into q-eq with 8.0 ± 0.8 ps lifetime, and internal conversion to S1. The fluorescence wavelength and lifetime from S1 are 442 nm and 3.6 ± 0.3 ns, respectively. In q-eq., relaxation from Sn to S1 occurs quickly in less than 1 ps and also S1 is generated by the structural change from q-ax. The fluorescence wavelength and lifetime from S1 are 576 nm and 16 ± 0.1 ns, respectively. Furthermore, the intersystem crossing (ISC) to T1 followed by the thermal RISC from T1 occurs and delayed fluorescence is observed with a 544 ± 12 nm lifetime. In THF, which has the high permittivity (ε = 7.58), the same three processes occur in q-ax. The fluorescence wavelength and lifetime from S1 are similar to those in toluene, 473 nm and 5.0 ± 0.7 ns, respectively. In contrast, the processes in q-eq. are different from those in toluene. The fluorescence wavelength from S1 is longer, ~675 nm, and its lifetime is shorter, 0.97 ± 0.01 ns, and no delayed fluorescence is observed. This is presumably because the reduced energy of S1 in high permittivity solvent accelerates non-radiative relaxation directly to S0 following the energy gap law.