Dimer Formation and Excitation Relaxation of Perylene in Langmuir−Blodgett Films

Steady-state and picosecond time-resolved fluorescence spectra of perylene have been measured in order to examine the dimer formation and the excitation relaxation in restricted geometries of Langmuir−Blodgett (LB) films. In LB films, perylene forms two types of dimers, D 1 and D 2, which are assigned to the dimers where two chromophores are partially and fully overlapped, respectively. At the concentration of 0.05 mol %, only the monomer fluorescence is observed. As the concentration is increased to 1 mol %, the excimer 1 fluorescence (from D 1 site) can be seen in the time region after 40 ns. At a concentration higher than 10 mol %, all three components including the excimer 2 fluorescence (D 2 ) are observed from the early stage of time. Their contributions to the steady-state and the time-resolved fluorescence spectra are dependent upon the concentration. The excitation transfer from M (monomer) and D 1 sites to the D 2 site occurs with a time constant of ∼50 ps at a concentration of 10 mol %, whereas it is ∼10 ps in the case of 50 mol %.