Synthesis and Characterization of New Conjugated Fluorenyl‐Porphyrin Dendrimers for Optics

Abstract

A new family of conjugated meso-tetraphenylporphyrin-based dendrimers with four (TPP1, TPP2), eight (TPP3, TPP4, TPP5) and up to sixteen (TPP6) fluorenyl groups has been synthesized and fully characterized. These tetraphenylporphyrin-cored dendrimers present peripheral alkynyl π-conjugated dendrons with fluorenyl termini. The meso-aryl rings of these porphyrins are functionalized either in para- (TPP1, TPP2, and TPP3) or meta-positions (TPP4, TPP5, and TPP6). Their detailed luminescence properties are discussed in reference to two porphyrins lacking fluorenyl dendrons (TPP-H1,2,3 and TPP-H4,5,6). A strong dependence of their luminescence quantum yield and lifetime on their structures is stated, their nonlinear optical properties were also discussed.

New Conjugated meso‐Tetrafluorenylporphyrin‐Cored Derivatives as Fluorescent Two‐Photon Photosensitizers for Singlet Oxygen Generation

“…Although the emission quantum yields are slightly diminished compared with that of the smaller TFP reference compound, we have shown that the brightness of TPP1 and TPP2 (expressed as ϵ × Φ F ) was much improved over that of TFP, a feature of interest for many applications. More interestingly, we have also provided evidenced that these dendrimers present remarkable two‐photon absorption (TPA) cross‐sections, which were significantly larger than those of TPP, especially in the case of compounds with fully conjugated arms, and that TPP1 and TPP2 sensitize oxygen quite efficiently . When taken together, these various observations strongly suggest that, once suitably functionalized, such molecular architectures (or closely related structures) might give rise to outstanding photosensitizers for various biomedical applications typical of porphyrin derivatives, such as one‐ or two‐photon– photodynamic therapy (PDT).…”

“…To synthetically access these new dendrimers, a strategy analogous to that previously used for the synthesis of TPP‐cored porphyrin dendrimers was adopted, which basically involves two steps; 1) the synthesis of dendritic aldehyde precursor, and 2) the formation of the porphyrin core by reaction with pyrrole …”

“…To obtain these new rigid intermediates named D1 – 3 (as well as the corresponding dendrimers) with suitable solubilities, n ‐butyl groups were appended at the 9‐position of the starting 2‐bromofluorene. Molecules 1 and 3 have previously been used by some of us during the synthesis of TPP‐cored porphyrin dendrimers . The Sonogashira coupling of these alkynes ( 1 and 3 ) with the bromo‐aldehyde 2 yielded, respectively, the new dendrons D1 and D2 in good yields (90 and 63 %, respectively).…”

“…UV/Vis absorption and emission spectra were next recorded for the new TFP‐cored porphyrin dendrimers TFP1 – 3 in toluene solutions (Table ). Molecules with similar structures, such as TFP‐Bu , TPP , TPP1 , and TPP2 , were chosen as references (Scheme ) to analyze the influence of various aromatic groups at meso ‐positions on the optical properties of these derivatives.…”

“…Remarkably, this simple compound exhibits a high fluorescence quantum yield (23–24 %) compared with the reference tetraphenylporphyrin (TPP; 11–12 %), demonstrating the good capacity of the fluorenyl units to enhance quantum yields by favoring the radiative process over nonradiative ones . In an attempt to further enhance the luminescence quantum yields of the central porphyrin core, we subsequently synthesized two series of substituted meso ‐substituted TPP‐based porphyrin dendrimers incorporating increasing number of fluorenyl units, featuring either nonconjugated ether linkers or fully conjugated alkynyl linkers, such as TPP1 and TPP2 (Scheme ), and also explored their photophysical properties . We could show that the various fluorene‐containing dendrons act as light‐harvesting antenna, before transferring their energy to the central porphyrin core, which eventually radiatively decays to the ground state by emission of a red fluorescence.…”