Fluorenyl porphyrins for combined two-photon excited fluorescence and photosensitization

Abstract

The two-photon absorption (2PA), the luminescence and the photosensitization properties of porphyrin-cored fluorenyl dendrimers and meso-substituted fluorenylporphyrin monomer, dimer and trimer are described. In comparison with model tetraphenylporphyrin, these compounds combine enhanced (non-resonant) 2PA cross-sections in the near infrared and enhanced fluorescence quantum yields, together with maintained singlet oxygen generation quantum yields. "Semi-disconnection" between fluorenyl groups and porphyrins (i.e. direct meso substitution) proved to be more efficient than non-conjugated systems (based on efficient FRET between fluorenyl antennae and porphyrins). These results are of interest for combined two-photon imaging and photodynamic therapy.

Phthalocyanine-Cored Fluorophores with Fluorene-Containing Peripheral Two-Photon Antennae as Photosensitizers for Singlet Oxygen Generation

“…d Literature value of φ F = 0.23 (± 0.03) determined via the comparative method using chlorophyll in diethylether as standard [29]. e In CH 2 Cl 2 [22,25].…”

“…We also observed that the various fluorene-containing dendrons act as light-harvesting antennae, before transferring their energy to the central porphyrin core. Although the emission quantum yields are slightly diminished compared to that for the smaller TFP reference compound [20], we showed that their brightness was much improved [26].Following our initial goal to further improve the luminescence quantum yield of the photosensitizers with flexible arms [22,23,25], we now wondered about the impact of replacing the porphyrin central core by a phthalocyanine ring. Based on literature reports, this tetrapyrrolic unit should be able to photosensitize oxygen with an efficiency similar to that of the meso-tetraarylporphyrin core once metalated by Zn(II) [27], but should also present a significantly improved fluorescence quantum yield [7].…”

“…In line with Fréchet's work [24], this "antenna effect" was stronger in dendritic assemblies such as H 2 OOFP or H 2 SOFP than in star-shaped architectures such as H 2 TOFP. As a result, new oxygen photosensitizers with significantly improved brightness over H 2 TPP could be obtained by these means [25]. Furthermore, the presence of several fluorenyl units at the periphery of the central macrocycle also allowed for a significant increase in the two-photon absorption (2PA) cross-section maximum at lowest energy, another very desirable feature when targeting PDT or theranostic applications in the near-infrared (NIR) range [14,15].We can notice that, after having studied these non-conjugated TPP-based porphyrin dendrimers featuring flexible ether linkers (Figure 1), we considered more recently porphyrin dendrimers with conjugated peripheral arms [26].…”

“…Following our initial goal to further improve the luminescence quantum yield of the photosensitizers with flexible arms [22,23,25], we now wondered about the impact of replacing the porphyrin central core by a phthalocyanine ring. Based on literature reports, this tetrapyrrolic unit should be able to photosensitize oxygen with an efficiency similar to that of the meso-tetraarylporphyrin core once metalated by Zn(II) [27], but should also present a significantly improved fluorescence quantum yield [7].…”

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

“…It should be emphasized that even higher TPAc ross-sections have already been obtained with other porphyrin systems, [23] exhibitingm ore efficient conjugation between the subchromophoric moieties, but generally along with strong modifications of the other photophysical properties, which limit their interest for theranostic applications.I ndeed, such compounds usually exhibit am odest to negligible fluorescence, as well as interfering residual one-photon absorption (OPA), which leads to the loss of some advantages of selectiveT PA,m ainly the 3D resolution. In contrast, fluorenyl-porphyrin dendrimers exhibit an improved trade-off [24] between selective( non-resonant) TPA cross-sectionsand fluorescenceproperties.…”