Quenching of Excited J Aggregates on Metals by Surface Plasmon Excitations

The photocurrent spectrum was measured for a solid-state organic photoelectric cell with ITO and Al electrodes. A large difference was observed between absorption and photocurrent spectra for merocyanine J aggregate Langmuir−Blodgett (LB) films as an organic photoconductor of the cell. The spectra indicate that the J aggregate in the LB film is not responsible for the photocurrent. To confirm the origin, the angular distribution of emission from the metal was measured using a coupler prism under the excitation of the J aggregates. P-polarized directional emission, which distinguishes surface plasmon polaritons (SP), was observed for a coupler prism/Al/LB film system. It is evident that excited J aggregates on metals are quenched by coupling with SP. The quenching seems to have a close relation with the difference between absorption and photocurrent spectra. The emission spectrum was also measured to compare with the fluorescence spectrum of the J aggregate LB film. The fluorescence spectrum was sharper and more Stokes-shifted than the emission based on SP. The emission process via SP seems to be less influenced by relaxation in the J aggregate.