Wavelength-Dependent Electron and Energy Transfer Pathways in a Side-to-Face Ruthenium Porphyrin / Perylene Bisimide Assembly

A new side-to-face supramolecular array of chromophores, where a pyridyl-substituted perylene bisimide dye axially binds to two ruthenium porphyrin fragments, has been prepared by self-assembly. The array is formulated as DPyPBI[Ru(TPP)(CO)] 2 , where DPyPBI )N ,N ′-di(4-pyridyl)-1,6,7,12-tetra(4- tert -butylphenoxy)perylene-3,4:9,10-tetracarboxylic acid bisimide and TPP ) 5,10,15,20-tetraphenylpor- phyrin. The photophysical behavior of DPyPBI[Ru(TPP)(CO)] 2 has been studied by fast (nanoseconds) and ultrafast (femtoseconds) time-resolved techniques. The observed behavior sharply changes with excitation wavelength, depending on whether the DPyPBI or Ru(TPP)(CO) units are excited. After DPyPBI excitation, the strong fluorescence typical of this unit is completely quenched, and time-resolved spectroscopy reveals the occurrence of photoinduced electron transfer from the ruthenium porphyrin to the perylene bisimide dye (ô ) 5.6 ps) followed by charge recombination (ô ) 270 ps).