Synthesis and time-resolved fluorescence study of porphyrin-functionalized gold nanoparticles

Free-base porphyrins with two thioacetate terminated linkers in different positions on the porphyrin molecule were synthesized and attached to tetraoctylammonium bromide (TOABr) stabilized gold nanoparticles with a core diameter of 5 nm. The different positions of the linkers affect the stability of the functionalized gold nanoparticles and have an effect on the packing density of the molecules on the nanoparticle surface. However, the intended control of the orientation of the porphyrin molecules relative to the gold nanoparticle surface is not well achieved with the chosen linkers. Fluorescence of the porphyrins is observed to be strongly quenched after the attachment to the nanoparticles. Fluorescence lifetimes of the porphyrin-functionalized gold nanoparticles were determined with the up-conversion method to be very short, 3–5 ps. The short fluorescence lifetimes indicate efficient energy transfer to the gold cores.