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Porphyrins participate as dienophiles in Diels-Alder reactions with ortho-quinodimethanes or pentacene. They can also behave as dipolarophiles in 1,3-dipolar cycloadditions with a range of 1,3-dipoles. These two reaction types were successfully used to synthesize novel chlorins, bacteriochlorins and isobacteriochlorins.

Second-order molecular hyperpolarizabilities (γ) of four tetraphenylchlorin derivatives were measured by the Z-scan technique at 784 nm in the off-resonant region and the enhancement in the hyperpolarizabilities of these derivatives in comparison to the regular porphyrins with the same external side-groups is explained on the basis of the difference in their Q-band oscillator strengths.

A series of β,β-dihydroxychlorins derived from meso-tetraphenylporphyrins (TPPs) have been synthesized. Their in vitro cytotoxicity has been measured and compared to BPDMA (verteporfin). Under the assay conditions BPDMA had an LD₅₀ (lethal dose to kill 50% of cells) value of 0.007 μM (5 ng/mL). The LD₅₀ values for the TPP derivatives varied from 1.7 × 10^-2 to 9.9 μM depending upon the substituents and their position on the phenyl groups. One example of the dihydroxychlorin prepared from unsubstituted 5,15-diphenylporphyrin was examined and this exhibited an LD₅₀ of 2.4 × 10^-3 μM!

A series of N-substituted porphyrins were synthesized either by direct alkylation of the symmetrical porphyrins or from the unsymmetrical porphyrins obtained via MacDonald's procedure using the appropriate N-substituted dipyrromethanes. Depending upon the nature of the peripheral substitutions in the porphyrin system, the nickel(II)-promoted rearrangement of these compounds gave either meso-substituted or unsubstituted Ni(II) porphyrins or chlorins. The chlorins and meso-substituted porphyrins were formed via the intramolecular migration of the N-substituent to carbon. This approach provides easy access for the synthesis of chlorins and the meso-substituted porphyrins, which are otherwise difficult to synthesize.

The reaction of carbohydrate-substituted α-diazoacetates with meso-tetrakis(pentafluorophenyl)porphyrinatozin(II) allows the synthesis of new glyco-hydroporphyrin derivatives.

Porphyrins and other pyrrolic macrocycles can participate in a range of pericyclic reactions. This review deals mainly with their use in Diels-Alder reactions (as dienes and dienophiles) and in 1,3-dipolar cycloadditions (as 1,3-dipoles and dipolarophiles)

Quantum chemistry methods were used to study the meta-tetra(hydroxyphenyl)chlorin (mTHPC) and its isomers. The mTHPC (Foscan®) is a commercial chlorin, used in photodynamic therapy (PDT) and is classified as a second-generation drug in PDT. The present work is to obtain quantum chemistry properties which can explain the high efficiency of the mTHPC compared with its isomers (ortho and para) and other chlorins. Based in the chemical hardness and ionization potential obtained from HOMO and LUMO orbitals energy, our results show that all chlorins have similar reactivity. Moreover, all chlorins have approximately the same capacity to storage energy in the triplet excited state, with energy differences between the ground state and the triplet excited state of 1.38, 1.39 and 1.36 eV for oTHPC, mTHPC and pTHPC, respectively. The calculated UV spectra (a very important quantity which can be correlated with the photosensitizer (PS) efficiency property), shows that the present chlorins all have a peak at 622 nm. Finally, after analysis of the dipole moment differences, between the three isomers, an explanation about the greater mTHPC efficiency in PDT, was possible. Due to its greater lipophilic character, mTHPC is absorbed by tumor cells to a greater degree than oTHPC and pTHPC. Our findings are consistent with literature and can be used to help new drug design for use in PDT.

The OsO₄-mediated dihydroxylation of quinoline-annulated porphyrin generates a quinoline-annulated dihydroxychlorin in a regioselective fashion. Its dihydroxypyrroline moiety, located at the opposite of the annulated pyrrole, is susceptible to the same functional group interconversions we previously demonstrated for non-annulated dihydroxychlorins: oxidations to the corresponding dione, lactone, and dialkoxymorpholine derivatives. The quinoline-annulated chlorin and derivatives are all characterized by absorption spectra that are much broadened and between 130 and 220 nm red-shifted compared to their non-annulated analogs. Absorbance maxima in the NIR up to well above 800 nm were recorded. We attribute the bathochromic shift to their extended $\pi$-systems and inferred non-planarity, highlighting that quinoline-annulation is a particularly effective and simple strategy to red-shift the absorption spectra of chlorins and chlorin analogs.

Porphyrin-based molecules are actively studied as dual function theranostics: fluorescence-based imaging for diagnostics and fluorescence-guided therapeutic treatment of cancers. The intrinsic fluorescent and photodynamic properties of the bimodal molecules allows for these theranostic approaches. Several porphyrinoids bearing both hydrophilic and/or hydrophobic units at their periphery have been developed for the aforementioned applications, but better tumor selectivity and high efficacy to destroy tumor cells is always a key setback for their use. Another issue related to their effective clinical use is that, most of these chromophores form aggregates under physiological conditions. Nanomaterials that are known to possess incredible properties that cannot be achieved from their bulk systems can serve as carriers for these chromophores. Porphyrinoids, when conjugated with nanomaterials, can be enabled to perform as multifunctional nanomedicine devices. The integrated properties of these porphyrinoid-nanomaterial conjugated systems make them useful for selective drug delivery, theranostic capabilities, and multimodal bioimaging. This review highlights the use of porphyrins, chlorins, bacteriochlorins, phthalocyanines and naphthalocyanines as well as their multifunctional nanodevices in various biomedical theranostic platforms.

Unlike N-confused porphyrins which are well-known and extensively studied tetrapyrroles, N-confused hydroporphyrins are almost unknown, largely because so far they have resisted attempts at rational synthesis. Here, we report our efforts towards the total synthesis of N-confused hydroporphyrins. We have prepared N-confused building blocks analogous to the non-N-confused substrates in the Lindsey synthesis of sparsely substituted chlorins. We have systematically flipped the A, B and C pyrrole rings in the dipyrrolic precursors of the target N-confused macrocycles, preparing in total an N-confused “Western half” (tetrahydrodipyrrin) and two N-confused “Eastern halves” (brominated formyldipyrromethanes). These were subjected to a range of cyclization conditions. While we successfully isolated and identified three macrocyclic products, none of these proved to be the desired N-confused hydroporphyrin.

Dihydroporphyrins or chlorins differ from porphyrins only by saturation of a peripheral double bond of the macrocycle. However, this small structural difference leads to a significant increase of the absorption band at approximately 650 nm, which makes them very interesting candidates for photodynamic therapy applications. The reduction of porphyrins bearing two, three or four pyridyl substituents with tin(II) chloride has been developed for the synthesis of dihydroporphyrins in yields of 15–73%. The reduction of 5-(aryl)-10,15,20-tris(2 or 4-pyridyl)porphyrin with tin(II) chloride dihydrate demonstrated good regioselectivity. Porphyrins with one meso-aryl bearing one electron-donating group (EDG) gave 5-aryl-10,15,20-tris(2- or 4-pyridyl)-17,18-dihydroporphyrins in 17–72% yield. Porphyrins with one meso-aryl bearing one or more electron-withdrawing groups (EWG) gave 5-aryl-10,15,20-tris(4-pyridyl)-17,18-dihydroporphyrins or 5-aryl-10,15,20-tris(4-pyridyl)-7,8-dihydroporphyrins in 15–21% yield and isobacteriochlorin. We have also proven the possibility of functionalizing these compounds to design new regioisomerically pure photosensitizers.

Arrays composed of BODIPY and hydroporphyrin (chlorin or bacteriochlorin) components feature multiple strong absorption bands across visible and near-IR regions, efficient energy transfer from BODIPY to hydroporphyrin moiety, and strong deep-red or near-IR emission. These properties make such arrays attractive candidates for a variety of applications, particularly in solar energy conversion and biomedicine. In this review, the molecular design, synthesis, and photophysical properties of BODIPY-hydroporphyrin arrays are described. Their applications as fluorescent probes for in vivo imaging are also discussed.

In this review paper, we discuss the basic results obtained by our teams for chlorophyll and its derivatives in concentrated solutions (up to C = 2 × 10${}^{-2}÷$ 2 × 10${}^{-1}$ M) as well as multiporphyrin complexes of various structures: chemical dimers, self-assembled triads and polymeric ordered aggregates. This discussion is based on steady-state, pico/femtosecond time-resolved measurements including also site selection spectroscopy at 1.8 K. The adequacy of various theoretical models describing the mechanisms of the non-radiative relaxation pathways (the energy transfer especially) at short interchromophoric distances is substantiated. In concentrated solutions, basic processes involving excited singlet and triplet states of pigments are considered (fluorescence concentration depolarization, the directed energy transfer in conditions of inhomogeneous broadening, the distant energy transfer with participation of excited triplet molecules at powerful excitation, etc.). For porphyrin chemical dimers at intercenter distances R$\approx$1.0 ÷ 1.26 nm, it is quantitatively shown, that the effective singlet-singlet energy transfer is fully described by the inductive resonance model and takes place without quantum losses. For porphyrin chemical dimers of various types, basic energy relaxation processes are considered: exchange d-$\pi$ effects, the exchange-resonance triplet-triplet energy transfer, and the directed energy transfer in conditions of inhomogeneous broadening. It is shown that in self-assembled porphyrin triads, the energy transfer and photoinduced charge separation are basic processes of electronic excitation energy relaxation. In polymeric-ordered aggregates of photosynthetic pigments, the incoherent “hot” migration with pair jump time of t${}_{\text{PM}}$$\sim$ 1 ÷ 6 ps under conditions of strong electron-phonon coupling takes place in the absence of dynamic correlation between the donor and the acceptor. Finally, we will give a short overview of related research work.

Porphyrin-based molecules are actively studied as dual function theranostics: fluorescence-based imaging for diagnostics and fluorescence-guided therapeutic treatment of cancers. The intrinsic fluorescent and photodynamic properties of the bimodal molecules allows for these theranostic approaches. Several porphyrinoids bearing both hydrophilic and/or hydrophobic units at their periphery have been developed for the aforementioned applications, but better tumor selectivity and high efficacy to destroy tumor cells is always a key setback for their use. Another issue related to their effective clinical use is that, most of these chromophores form aggregates under physiological conditions. Nanomaterials that are known to possess incredible properties that cannot be achieved from their bulk systems can serve as carriers for these chromophores. Porphyrinoids, when conjugated with nanomaterials, can be enabled to perform as multifunctional nanomedicine devices. The integrated properties of these porphyrinoid-nanomaterial conjugated systems make them useful for selective drug delivery, theranostic capabilities, and multimodal bioimaging. This review highlights the use of porphyrins, chlorins, bacteriochlorins, phthalocyanines and naphthalocyanines as well as their multifunctional nanodevices in various biomedical theranostic platforms.

Dihydroporphyrins or chlorins differ from porphyrins only by saturation of a peripheral double bond of the macrocycle. However, this small structural difference leads to a significant increase of the absorption band at approximately 650 nm, which makes them very interesting candidates for photodynamic therapy applications. The reduction of porphyrins bearing two, three or four pyridyl substituents with tin(II) chloride has been developed for the synthesis of dihydroporphyrins in yields of 15–73%. The reduction of 5-(aryl)-10,15,20-tris(2 or 4-pyridyl)porphyrin with tin(II) chloride dihydrate demonstrated good regioselectivity. Porphyrins with one meso-aryl bearing one electron-donating group (EDG) gave 5-aryl-10,15,20-tris(2- or 4-pyridyl)-17,18-dihydroporphyrins in 17–72% yield. Porphyrins with one meso-aryl bearing one or more electron-withdrawing groups (EWG) gave 5-aryl-10,15,20-tris(4-pyridyl)-17,18-dihydroporphyrins or 5-aryl-10,15,20-tris(4-pyridyl)-7,8-dihydroporphyrins in 15–21% yield and isobacteriochlorin. We have also proven the possibility of functionalizing these compounds to design new regioisomerically pure photosensitizers.

Unlike N-confused porphyrins which are well-known and extensively studied tetrapyrroles, N-confused hydroporphyrins are almost unknown, largely because so far they have resisted attempts at rational synthesis. Here, we report our efforts towards the total synthesis of N-confused hydroporphyrins. We have prepared N-confused building blocks analogous to the non-N-confused substrates in the Lindsey synthesis of sparsely substituted chlorins. We have systematically flipped the A, B and C pyrrole rings in the dipyrrolic precursors of the target N-confused macrocycles, preparing in total an N-confused “Western half” (tetrahydrodipyrrin) and two N-confused “Eastern halves” (brominated formyldipyrromethanes). These were subjected to a range of cyclization conditions. While we successfully isolated and identified three macrocyclic products, none of these proved to be the desired N-confused hydroporphyrin.