A perylenetetracarboxylic diimide (PDI) trimer (3) linked by a triazine ring has been prepared. The UV-vis absorption spectra together with the H-1 NMR spectra revealed that two of the three PDI subunits in the trimer presents a face-to-face stacked configuration while the third one appended acts as a monomer. There is no strong interaction between the dimer and monomer at ground state. However, the fluorescence of the monomer was quenched efficiently by the dimer. The transient absorption and excitation spectra of this compound suggest that the energy transfer from the excited states of monomer to an excimer like state of dimer is responsible for this quick and efficient fluorescence quenching. The rate of the energy transfer is comparable to that from B800 to B850 in LH2.