The geometries of the ground and the first singlet excited states of the tetrahydropyrene derivatives were optimized respectively by the density functional theory (the used functional is B3LYP) and the single-excitation configuration interaction (CIS) method combining the 6-31＋G* basis set. According to the corresponding optimized structures, the absorption and emission spectra in different solvents are calculated using the time dependent density functional theory with the 6-311＋＋G** basis set. The solvent effect is considered by the polarizable continuum model. Inspection of the geometries reveals that, in acidic medium, the nitrogen atom located on the dimethylamino group of the THP can be protonated easily in the ground state. The calculated results indicate that the THP is not a dual fluorescence molecule, although its first excited state is a charge transfer (CT) state. In the presence of acidic solvents, the two emission bands of the THP are originated from two compounds, that is, the emission band at 2.71 eV is from the excited THP, and the fluorescence band at 3.69 eV from the protonated form of the THP. The absorption and decay pathways of the THP in acidic solvent are suggested based on the theoretical calculations. The calculated absorption and emission spectra are in good agreement with the experimental observations.

Key words: tetrahydropyrene derivative, absorption and emission spectra, dual fluorescence, electronic structure, neutral and acidic solvents, excitation and decay pathways