Synthesis and photophysical properties of porphyrins with fluorenyl pendant arms

Giant Star-shaped meso-substituted Fluorescent Porphyrins with Fluorenyl-containing Arms Designed for Two-photon Oxygen Photosensitization

In the continuation of previous studies on carbon-rich meso-tetraarylporphyrins featuring 2,7-fluorene units at their periphery, the effect of changing the peripheral dendritic arms for linear arms on their oxygen-photosensitizing ability, their fluorescence and their two-photon absorption (2PA) properties is now analyzed. Thus, starburst porphyrins possessing up to twenty conjugated fluorenyl units were isolated and studied. More precisely, a series of five new free-base porphyrins featuring fully conjugated arms incorporating an increasing number of fluorenyl groups connected via 1,2-alkenyl spacers were synthesized, along with their Zn(II) complexes. Upon excitation in the arm-centred π-π* absorption band, an efficient energy transfer takes place from the peripheral fluorenyl units to the central porphyrin core, leading to intense red-light emission and oxygen photosensitization by the latter. More interestingly, while the linear optical properties of these porphyrins were only slightly improved compared to those of their dendrimer analogues for photodynamic therapy (PDT) or fluorescence imaging, their 2PA cross-sections were much more significantly boosted, evidencing the key role played by different structures on nonlinear optical properties. Finally, by comparison with other porphyrin-based two-photon photosensitizers reported in the literature, we show that these new "semi-disconnected" starburst systems exhibit a remarkable trade-off between intrinsic 2PA, fluorescence and oxygen photosensitization.

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

A series of free base and Zn(II) phthalocyanines featuring fluorenyl antennae linked by methoxy or oxo bridges to the phthalocyanine core (Pc) were synthesized and characterized. Selected linear and nonlinear (two-photon absorption) optical properties of these new compounds were subsequently studied. As previously observed for related porphyrin dendrimers bearing 2-fluorenyl peripheral dendrons, an efficient energy transfer occurs from the peripheral antennae to the central phthalocyanine core following excitation in the fluorenyl-based π–π* absorption band of these chromophores. Once excited, these compounds relax to the ground state, mostly by emitting intense red light or by undergoing intersystem crossing. As a result, the tetrafunctionalized Zn(II) phthalocyanines are fluorescent, but can also efficiently photosensitize molecular oxygen in tetrahydrofurane (THF), forming singlet oxygen with nearly comparable yields to bare Zn(II) phthalocyanine (ZnPc). In comparison with the latter complex, the positive role of the fluorenyl-containing antennae on one- and two-photon brightness (2PA) is presently demonstrated when appended in peripheral (β) position to the phthalocyanine core. Furthermore, when compared to known porphyrin analogues, the interest in replacing the porphyrin by a phthalocyanine as the central core to obtain more fluorescent two-photon oxygen photosensitizers is clearly established. As such, this contribution paves the way for the future development of innovative biphotonic photosensitizers usable in theranostics.

New porphyrin dendrimers with fluorenyl-based connectors: a simple way to improving the optical properties over dendrimers featuring 1,3,5-phenylene connectors

Dendrimers with new fluorenyl-based connectors have been synthesized and characterized. Their detailed luminescence properties and selected photophysical properties are discussed in the frame of two-photon-induced theranostics.

Carbon-bridged Oligo(phenylenevinylene)s as Light-harvesting Antenna for Porphyrins

The efficacy of carbon-bridged oligo(phenylenevinylenes)s (COPVs) as light-harvesting antenna for porphyrins is demonstrated using a series of 5,15-di-COPVn-substituted free-base and zinc porphyrins, COPVn-MP-COPVn (n=1-3, M=H₂ , Zn). These molecules were synthesized by Suzuki-Miyaura cross-coupling reactions of COPVn-Bpin and Br-H₂ P-Br. The absorption spectra of these compounds in solution show a significant expansion of the Soret band region together with a bathochromic shift of the Q band, suggesting a significant interaction between these chromophores in the ground state. The photoluminescence quantum yield of the porphyrin-COPV conjugates is enhanced up to four times relative to the parent porphyrins. Theoretical calculations also indicated interactions between these chromophores in the HOMO, which suggests that the light-harvesting ability stems from the expansion of the π-electron-conjugation system.

Difluorenyl carbo-Benzenes: Synthesis, Electronic Structure, and Two-Photon Absorption Properties of Hydrocarbon Quadrupolar Chromophores

The synthesis, crystal and electronic structures, and one- and two-photon absorption properties of two quadrupolar fluorenyl-substituted tetraphenyl carbo-benzenes are described. These all-hydrocarbon chromophores, differing in the nature of the linkers between the fluorenyl substituents and the carbo-benzene core (C-C bonds for 3 a, C-C=C-C expanders for 3 b), exhibit quasi-superimposable one-photon absorption (1PA) spectra but different two-photon absorption (2PA) cross-sections σ2PA. Z-scan measurements (under NIR femtosecond excitation) indeed showed that the C≡C expansion results in an approximately twofold increase in the σ2PA value, from 336 to 656 GM (1 GM = 10(-50) cm(4) s molecule(-1) photon(-1)) at λ = 800 nm. The first excited states of Au and Ag symmetry accounting for 1PA and 2PA, respectively, were calculated at the TDDFT level of theory and used for sum-over-state estimations of σ2PA(λi), in which λi = 2 hc/Ei, h is Planck's constant, c is the speed of light, and Ei is the energy of the 2PA-allowed transition. The calculated σ2PA values of 227 GM at 687 nm for 3 a and 349 GM at 708 nm for 3 b are in agreement with the Z-scan results.

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

Thanks to its 2-ethynylflorenyl-containing arms, dendrimer 1 sensitizes molecular oxygen in 70% yield and exhibits a fluorescence yield of 20%.

Multiply biphenyl substituted zinc(II) porphyrin and phthalocyanine as components for molecular materials

The preparation and physico-chemical characteristics of zinc(II) porphyrin and phthalocyanine derivatives with biphenyl units are reported. These compounds have been prepared as components for molecular electronics systems and rotor-based molecular machines, where the biphenyl units can act as paddles because they are oriented quasi-perpendicularly to the plane of the aromatic macrocycles which would be coordianted through the transition metal ion by an axial ligand. The minimalist design along with the absence of solubilizing groups leads to a low solubility of the compounds in organic solvents; the phthalocyanines is only sparingly soluble while the porphyrin is more easily manipulated, but in any case the concentration of both compounds is sufficient for surface deposition. The luminescence of the compounds is characteristic of the central unit, although it is clear in the absorption spectra that the phthalocyanine derivative has a particularly strong tendency to aggregate non-specifically. The porphyrin forms microcrystals while the phthalocyanines which bears eight biphenyl units forms amorphous aggregates from 1,2-dichlorobenzene reminiscent of glasses of other biphenyl derivatives, which is interesting for the preparation of amorphous materials for optics applications.

Self-organized nanofibers and nanorods of porphyrins bearing hydrogen bonding motifs

Porphyrins bearing uracyl motifs at the four meso positions self-organize via homo-complementary hydrogen bonds and pi-stacking into nanofibers, nanorods and thin films on mica and glass surfaces depending on deposition conditions.