Dendritic molecular assemblies for singlet oxygen generation: meso-tetraphenylporphyrin-based biphotonic sensitizers with remarkable luminescence

Abstract

International audienceFour new TPP-based chromophores (1-4) peripherally functionalized with dendrons contg. 2-fluorenyl groups were studied for their potential to serve in photodynamic therapy. Their linear and nonlinear optical properties were investigated. With significant TPA cross-sections at 790 nm, good singlet oxygen generation capabilities and relatively large intrinsic fluorescence, sensitizers such as 1 might become particularly appealing for theranostics

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.…”