New fluorescent tetraphenylporphyrin-based dendrimers with alkene-linked fluorenyl antennae designed for oxygen sensitization

The design of porphyrin-based dendrimers featuring conjugated fluorenyl dendrons via alkene spacers allows evaluating the importance of the role of these spacers on the optical properties of interest. In the continuation of previous studies, a second-generation porphyrin-based dendrimer was synthesized and metalated by Zn(II) along with its known first-generation homologue. The targeted free-base porphyrin was obtained by repetitively cycling a Michaelis–Arbuzov reaction and a Horner–Wadsworth–Emmons reaction to construct the desired vinyl-containing dendrons. After metalation by Zn(II), meso-tetraphenylporphyrin-cored dendrimers with eight (ZnTPP-D1) and sixteen (ZnTPP-D2) fluorenyl arms at their periphery were eventually isolated. These species allow evaluating the influence of the central metal and of the 1,2-alkyne for 1,2-alkene exchange on fluorescence, oxygen photosensitization, and two-photon absorption. Such structure–property relationships are currently needed for the design of optimal dendrimeric photosensitizers allowing combined two-photon-based photodynamic therapy (2P-PDT) and imaging.