Synthesis and excited-state photodynamics of perylene-porphyrin dyads part 3. Effects of perylene, linker, and connectivity on ultrafast energy transfer

New perylene-porphyrin dyads have been designed that exhibit superior light-harvesting and energy-utilization activity compared with earlier generations of structurally related dyads. The new dyads consist of a perylene mono(imide) dye (PMI) connected to a porphyrin (Por) via an ethynylphenyl (ep) linker. The PMI-ep-Por arrays were prepared with the porphyrin as either a zinc or magnesium complex (Por = Zn or Mg) or a free-base form (Por = Fb). The absorption properties of the perylene complement those of the porphyrin. Following excitation of the perylene (forming PMI*) in toluene, each array exhibits ultrafast (k_ENT ≥ (0.5 ps)^-1) and essentially quantitative energy transfer from PMI* to the ground-state porphyrin (forming Por*). In each of the arrays, the properties of the excited porphyrin (lifetime, fluorescence yield, etc.) are basically unperturbed from those of the isolated pigment. Thus, following energy transfer, the excited porphyrin is not quenched by deleterious reactions involving the perylene accessory unit that would otherwise limit the ability of Por* to emit light or transfer energy to another stage in a molecular photonic device. Collectively, the PMI-ep-Por dyads represent the successful result of a molecular design strategy to produce arrays with excellent properties for use as light-input and energy-transduction elements for applications in molecular optoelectronics.