Figure compares the UV-Vis absorption and steady-state PL spectra of PTZ-TRZ in toluene and THF. The two bands at ~290 nm and 363 nm in the absorption spectra are located at almost the same wavelengths both in toluene and in THF, indicating that the optical transitions from S0 are independet of solvent or permittivity. In contrast, the PL spectra depend largely on the solvent. The PL spectra in both solutions show dual emission and their bands are located at 422 nm and 576 nm in toluene and at 453 nm and 675 nm in THF. According to the quantum chemical calculations, the emission bands at 453 and 675 nm are assigned to the emissions from q-ax. and q-eq., respectively . Both the emission bands are red-shifted in the higher permittivity solvent (THF), indicating that the excited-state energies of both the conformers are stabilized by the solvation. Thus, both the two excited states showing these emissions are assigned to CT excited states. This result is consistent with the previous reports .