Quenching of porphyrin excited states by adjacent or distant porphyrin cation radicals in molecular arrays

The quenching of photoexcited porphyrins by porphyrin cation radicals at ad jacent or distant sites in diphenylethyne-linked porphyrin dyads and triads has been studied using static and time-resolved optical spectroscopy. The excited-state quenching is highly efficient in all cases (> 99%) and occurs in less than or equal to 11 ps between adjacent sites (by through-bond ene rgy/charge transfer) and in less than or equal to 55 ps between distant sit es (likely by superexchange-assisted energy transfer). The rates can be tun ed using the porphyrin-linker connection motif. These results should prove useful in the design of arrays that use electro- or photo-chemically genera ted porphyrin cation radicals for molecular switching and other application s in molecular photonics. (C) 2001 Elsevier Science B.V. All rights reserve d.