The photoinduced transient states of mixed octadecylrhodamine B (R) and 2-(9-anthroyloxy) stearic acid (A) Langmuir-Blodgett (LB) films are studied by the flash photolysis method, The R molecules in LB films exist predominantly as dimers. The triplet state of the R dimer decays by reactions, which partly directly regenerates the dye in the ground state and partly produces a dimer radical pair, In the presence of A, an electron-hole pair is formed by an electron transfer from A to the excited singlet state of R.