Journal of Porphyrins and Phthalocyanines

Photodynamic therapy (PDT) is a minimally invasive technique for the treatment of target malignant tumors via the generation of highly reactive singlet oxygen species. PDT treatment of cancer/tumor tissues greatly relies on the development of suitable stable, highly specific and efficient photosensitizers. BODIPY (Boron dipyrromethene) derivatives, as a class of well-developed, versatile fluorescent dyes, has emerged as a new class of PDT agents over the past decade. Many elegant strategies have been developed to enhance the singlet oxygen generation efficiency and the cancer/tumor cell selectivity of BODIPY-based photosensitizers to improve the therapeutic outcomes as well as to minimize the side effects. Many of the currently reported BODIPY-based photosensitizers are valuable dual imaging and therapeutic agents, which can efficiently generate singlet oxygen for PDT and emit fluorescence for in vivo imaging. Although the currently approved PDT agents used for clinical trials do not feature BODIPYs, this situation is expected to change. In this review, we provide an overview of the various strategies that have been used to improve the singlet oxygen generation efficiency for tuning BODIPY fluorophores into photosensitizers and dual imaging/therapeutic agents. Their photophysical properties and photocytotoxic activity including the absorption/emission wavelengths, the singlet oxygen generation efficiency (${\mathrm{\Phi }}_{\mathrm{\Delta }})$ and the half maximal inhibitory concentration $({\mathrm{\text{IC}}}_{50})$ of these currently reported photosensitizers are summarized. We believe these newly developed BODIPY-based photosensitizers will broaden current concepts of strategies for PDT agent design, and promise to make an important contribution to the diagnosis and therapeutics for the treatment of cancer.

In the present review, we discuss the results of the research we have done over the last decade on multi-porphyrinic architectures bearing a nucleotidic backbone, compare all the data, offer a novel overview, and emphasize common capabilities of nucleosides appearing in various systems, providing a new insight on the pre-organizing capabilities of nucleosidic backbones. The efficiency of nucleosides as pre-organizing agents was investigated through the synthesis and study of various bis-porphyrins bearing nucleosidic linkers, as well as through the investigation of the conformation of linear and arborescent multi-porphyrins constructed on a nucleosidic backbone. The capacity of these molecules to complex guests with a high association constant was used as a tool to evaluate their degree of pre-organization, as well as the investigation of the electronic coupling existing between their chromophores and their photo-chemical capacities. Such an overview of one decade of scientific investigations documents the fact that rigid linkers between chromophores are not necessary for their spatial pre-organization, opening new routes to the faster synthesis of flexible highly pre-organized molecular architectures avoiding the long and tedious synthesis of rigid tweezers, especially for the preparation of rigid linkers which may bring solubility and stability problems.

While dipyrrin-boron complexes (BODIPYs) and their derivatives have attracted much attention, dipyrrin-based metal complexes recently appeared as a novel luminescent material. So far, dipyrrin-metal complexes have been regarded as non-luminescent or weakly luminescent. Interestingly, introduction of steric hindrance at the meso-position and the development of heteroleptic complexes with proper frontier orbital ordering are two recent strategies that have been developed to improve their luminescent ability. Compared with BODIPYs, one of the distinctive advantages of dipyrrin-metal complexes is that they can form a series of self-assembled supramolecules and polymer assemblies via facile coordination reactions. In recent times, several supramolecular, coordination polymers and Metal-Organic Frameworks (MOFs) have been developed, $e.g.$ by spontaneous coordination reactions between dipyrrin ligands and metal ions. As a novel luminescent material, dipyrrin-metal complexes have been applied in many fields. This review article summarizes recent developments in dipyrrin-metal complexes from the viewpoint of the improvement of luminescent ability, the formation of supramolecular and coordination polymers and their potential applications.

Co2Pc2 (2) and Zn2Pc2 (3) were obtained in DMF and LuPc2 (4) was obtained in hexanol by the cyclotetramerization of novel diphthalonitrile (1). Synthesized compounds were characterized by FT-IR, ¹H-NMR, elemental analyses, MALDI-TOF MS and UV-vis spectroscopy techniques. Optimized geometries and electronic structures for compounds 2, 3 and 4 were investigated by Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT). In compound 2, a new bond was observed between Co centers forming two Co(III) with the interaction of d orbitals. Computational and experimental UV-vis spectra in DMF were found in agreement for the investigated compounds. Vertical and adiabatic ionization potentials for the studied systems were also calculated. The gate dielectric performances of thin films obtained from these compounds were investigated by fabricating ITO/2–4/Au devices. The observed reverse bias J-V characteristics revealed that the leakage current in ITO/2–4/Au devices is because of the Poole–Frenkel effect. The effect of the gate dielectric on the OFET performance parameters was also investigated by fabricating bottom-gate top-contact OFET using pentacene as the active layer. Maximum field effect mobility was observed with the 2-based OFET device. Calculated HOMO–LUMO gap, hole reorganization energy and ionization energy have also supported the experimental results which indicate that 2 is the most suitable system for OFET devices.

A series of hybrid catalysts for the oxygen reduction reaction (ORR) has been investigated. They are composed of multi-wall carbon nanotubes (MWNTs) coated with iron strapped porphyrins. Two porphyrins have been probed; both are strapped with the same skeleton and differ only by the number of overhung carboxylic acid(s), either one or two. In this structure, the carboxylic acid group can act as a proton relay between the medium and the catalyst or as a polar group surrounding the dioxygen binding cavity. While the number of carboxylic acid group(s) does not exhibit a significant influence on the catalytic properties, the combination of both components–MWNTs and porphyrin–leads to a better catalytic activity than those of the nanotubes or the porphyrins taken separately.

Zinc methyl 3-(methyl/ethylamino)methyl-pyropheophorbides-$a$ were prepared as models of photosynthetically active bacteriochlorophyll-$d$ possessing the 3${}^{\mathrm{\text{1}}}$-hydroxy group. The synthetic methylamino analog predominantly dimerized via two Zn${}^{\mathrm{\text{..}}}$N coordination bonds in aqueous Triton X-100 micelles, while the more sterically crowding and less coordinating ethylamino derivative self-aggregated to form large oligomers through single coordination and hydrogen bonds, Zn${}^{\mathrm{\text{..}}}$N–H${}^{\mathrm{\text{..}}}$O=C-13, similarly as in the natural self-aggregates of bacteriochlorophyll-$d$. The artificial self-aggregates were dependent on the aqueous pH, but the dimer was less pH-sensitive and also more tolerant to the additional Triton X-100.

We report two corrole based donor–acceptor (D–A) dyads, Cbz-Cor and Ptz-Cor to understand the energy/electron transfer reactions. In these D–A systems, the donor, either carbazole (Cbz) or phenothiazine (Ptz), is covalently connected at the meso-phenyl position of 10-(phenyl)-5,15-bis-(pentafluorophenyl)corrole (Ph-Cor) by C–N linkage. Both the dyads were characterized by ¹H NMR, MALDI-TOF MS, UV-vis, electrochemical, computational methods, study state fluorescence and TCSPC techniques. A comparison of absorption spectra with their reference monomeric compounds (Cbz-Ph, Ptz-Ph and Ph-Cor) revealed minimal ground-state interactions between chromophores in both dyads. Fluorescence studies suggested that singlet–singlet energy transfer from ¹Cbz* to corrole is the major photochemical pathway in the Cbz-Cor dyad with a quenching efficiency of $\sim$99%. Detailed analysis of the data suggests that Forster’s dipole–dipole mechanism does not adequately explain this energy transfer. However, at a 410 nm excitation, florescence quenching is detected in Ptz-Cor (49%) supporting a photo induced electron transfer (PET) process from the ground state of PTZ to the excited state of corrole macrocycle. The electron-transfer rates ($k_{ET})$ of Ptz-Cor are found in the range $0.6\times 10^7$ to $1.24\times 10^8{\mathrm{\text{s}}}^{-1}$ and are concluded to be solvent dependent.

Manganese corroles with the Mn atom in the oxidation states +III and +IV have been probed as donor moieties for supramolecular stacked donor–acceptor complexes with the typical acceptor units TCNQ (tetracyanoquinone), TCNP (tetracyanopyrazine), and TCNB (tetracyanobenzene). Four new compounds formed as single crystals from different co-crystallization attempts. In those cases where a Mn(III) corrole was used as the donor component, hydrolyzed and/or oxygenated compounds [(cor)Mn(TCNQ*)] and [(cor*)Mn(TCNP*)] were obtained as the exclusive products. With chloridomanganese(IV) corroles, sandwich-like 2:1 complexes [(cor)MnCl]${}_{\mathrm{\text{2}}}$[TCNQ] and [(cor)MnCl]${}_{\mathrm{\text{2}}}$[TCNB] form, with both components left intact. Crystallographic analyses reveal partial or complete charge transfer to unusual axial ligands and thus prove the high reactivity of Mn(III) corroles in the first two cases. For the sandwich arrangements, almost-unaltered geometric parameters of the Mn(IV) corroles are observed, pointing to negligible structural consequences for metal corroles when engaged in stacking interactions.

We have examined the effects of changing the temperature on the structure of a six-coordinate (tetraphenylporphinato)iron(II) complex, [Fe(TPP)(1-MeIm)(CO)] C${}_{\mathrm{\text{6}}}$H${}_{\mathrm{\text{6}}}$. In particular, we examined whether the coordination group parameters, $i.e$. the Fe–C and C–O parameters showed any effects. The study, carried out between 100 and 330 K, revealed no effect on those coordination group parameters. The axial Fe–N(Im) bond distance showed a small effect. The peripheral phenyl groups show a somewhat larger bond distance effect with bond distance increases of 0.02 to 0.03 Å. The population of the disordered solvent molecule favors one site as the temperature is lowered.

We have prepared crystals of [Fe(TTP)(NO)] (TTP = tetratolylporphyrin), a five-coordinate nitrosyl complex and determined its crystal and molecular structure at two temperatures. The crystal structure at 100 K reveals two independent molecules in the asymmetric unit of the structure. One molecule is completely ordered and the second molecule has a moderately disordered nitrosyl ligand. Both molecules show similar structural features: a substantial off-axis tilt of the Fe–N(NO) bond and an asymmetry of the equatorial Fe–N${}_{\mathrm{\text{p}}}$ bonds that is correlated with the tilt. The axial Fe–N(NO) bond distances are 1.7230 (9) and 1.7210 (10) Å; the Fe–N–O bond angles are 141.62 (8) and 140.04 (10)${}^{\circ }$. Determination of the structure at ambient temperature (293 K) showed an unexpected phase change, a crystal structure with one molecule per asymmetric unit containing the superposition of the two molecules at lower temperature. However, there was an increase in the NO disorder.

New Fe${}^{\text{II}}$ complexes of formula [Py₈TPyzPzFe] · xH₂O, its bis-pyridine adduct [Py₈TPyzPzFe(py)₂] · xH₂O, the pentanuclear species [(MCl${}_2{)}_4$Py₈TPyzPzFe] · xH₂O (M $=$ Pd${}^{\text{II}}$, Pt${}^{\text{II}})$ and the bis-DABCO adducts [Py₈TPyzPzFe(DABCO)₂] · 11H₂O and [(PdCl${}_2{)}_4$Py₈TPyzPzFe(DABCO)₂] · H₂O (Py₈TPyzPz $=$ octapyridino-tetrapyrazinoporphyrazinato dianion; DABCO $=$ 1,4-diazabiciclo[2.2.2]octane) were synthesized and characterized by elemental and thermogravimetric analysis, IR and UV-vis spectroscopy, with added studies on the starting complex [Py₈TPyzPzFe] · xH₂O regarding magnetic and electrochemical behavior. Clathrated water molecules are present in all compounds and have little to no effect on their physicochemical behavior as was observed for all previously reported analogs. UV-vis spectra of the mononuclear [Py₈PyzPzFe] · xH₂O complex in DMSO and pyridine are indicative of aggregation immediately after dissolving the compound. However, the spectra change slowly over time leading to formation of a porphyrazine species having spectral features typical of a monomer. UV-vis spectra of the parent pentanuclear [(MCl${}_2{)}_4$Py₈TPyzPzFe] · xH₂O (M $=$ Pd${}^{\text{II}}$, Pt${}^{\text{II}})$ complexes show a smaller degree of aggregation upon dissolution in DMSO or pyridine and the spectra of these solutions also change over time to those of a monomer. The presence of aggregation, spectral evolution with time and final species formed from the N-base adducts [Py₈TPyzPzFe(DABCO)₂] · 11H₂O and [(PdCl${}_2{)}_4$Py₈TPyzPzFe(DABCO)₂] · H₂O are reported and discussed.

We report routes towards synthesis of novel $\pi$-conjugated freebase cobalt, copper, gallium and manganese meso-alkynylcorroles. UV-vis spectra show that extensive peak broadening, red shifts, and changes in the oscillator strength of absorptions increase with the extension of $\pi$-conjugation. Using density functional theory (DFT), we have carried out a first theoretical study of the electronic structure of these metallocorroles. Decreased energy gaps of about 0.3–0.4 eV between the HOMO and LUMO orbitals compared to the corresponding copper, gallium and manganese meso-5,10,15 triphenylcorrole are observed. In all cases, the HOMO energies are nearly unperturbed as the $\pi$-conjugation is expanded. The contraction of the HOMO–LUMO energy gaps is attributed to the lowered LUMO energies.

In the present work, we determined the electrical properties of octachlorinated metallophthalocyanines with Co(II) and Cu(II) ions as metal centers. We engaged them in heterojunctions, with lutetium bisphthalocyanine as a partner. Surprisingly, cobalt and copper complexes show opposite behaviors, the first being an $n$-type material whereas the latter is a $p$-type material, as deduced from the response of the heterojunctions towards ammonia; showing the unusual key role played by the metal center. While the LuPc${}_{\mathrm{\text{2}}}$/Cu(Cl${}_{\mathrm{\text{8}}}$Pc) complex exhibits a negative response to ammonia, the LuPc${}_{\mathrm{\text{2}}}$/Co(Cl${}_{\mathrm{\text{8}}}$Pc) complex exhibits a positive response to ammonia, with a sensitivity of 1.47% ppm${}^{\mathrm{\text{-1}}}$ at concentrations lower than 10 ppm and a limit of detection of 250 ppb. All the devices operate at room temperature and in real atmosphere.

Supramolecular adducts formed by a commercial porphyrin derivative and silver nanoparticles have been obtained using exclusively light as an external trigger that is able to promote the formation of the plasmonic nanostructures. In particular, a water-soluble porphyrin, i.e. tetrakis(4-carboxyphenyl)porphyrin, has been used. It has been thoroughly characterized by means of UV-vis and fluorescence spectroscopy in order to explain its peculiar behavior when illumined with visible photons. Herein we demonstrate that, by means of light illumination, it is possible to tune the porphyrin aggregation state. Furthermore, when the monomeric form of the organic macrocycle is induced and a controlled amount of AgNO${}_{\mathrm{\text{3}}}$ is simultaneously dissolved, it is possible to promote the formation of silver nanostructures using visible light. The proposed approach allowed porphyrin derivatives/Ag nanoparticles hybrid nanostructures to be obtained without using a chemical reducing agent: the porphyrin derivative simultaneously acts as reducing agent when irradiated by visible light and as a capping agent for the silver nanostructures. The organic/inorganic adduct was characterized by means of steady-state fluorescence that highlights a strong energetic or electronic communication between the two species. XRD and SEM investigations evidence that silver nanoparticles are formed without using any reducing agent.

Steady-state fluorescence measurements and quantum-chemical DFT geometry optimizations are applied to extend the structure–property relationships between the free-base corrole macrocycle conformation and its basicity to the lowest excited S${}_{\mathrm{\text{1}}}$ and T${}_{\mathrm{\text{1}}}$ states. Direct basicity estimation in the lowest excited S${}_{\mathrm{\text{1}}}$ state is demonstrated by means of fluorescence quantum yield measurements. The long wavelength T1 tautomer is found to retain its basicity in the S${}_{\mathrm{\text{1}}}$ state, whereas the short wavelength T2 tautomer shows a noticeable decrease in basicity in the S${}_{\mathrm{\text{1}}}$ state, which is related to the in-plane tilting of the pyrrole ring to be protonated. The conformational changes upon going from the ground to the lowest excited T${}_{\mathrm{\text{1}}}$ state and the influence of the meso-aryl substitution pattern on the overall degree of distortions and tilting of the pyrrole ring to be protonated are also discussed from the point of view of macrocycle basicity.

In this study, a series of diphenylalanine tetra-substituted porphyrin derivatives were synthesized and their self-assembly ability was extensively studied. Apart from investigating the impact of incorporating many peptide moieties onto a porphyrin molecule; another perspective was investigated as well, namely the connection of two different chromophore entities (porphyrin and BODIPY) onto the same diphenylalanine molecule. Interestingly, various supra-molecular nanostructures were observed depending on the solvent mixture as well as the protecting group of the peptides, namely spheres, plaques and fibrils. The obtained self-assemblies were studied via UV-vis absorption and emission spectroscopies. Mainly red shifting was observed, indicating the formation of $J$-aggregates in the self-assembled state. However, in one case a blue shifted UV-vis spectrum was obtained suggesting the formation of $H$-type aggregates. Concerning the porphyrin-diphenylalanine-BODIPY derivative, additional fluorescence studies were performed in order to examine a possible interaction between the two chromophores in the excited state. Indeed, the emission measurements indicated that upon photo-excitation of the BODIPY entity, a very efficient energy or electron transfer process takes place from the BODIPY molecule to the porphyrin macrocycle.

We report two synthetic pathways for the preparation of 1,2-dicyanoferrocene, in a search for new dinitrile-based precursors that could be useful in the synthesis of metallocene-containing azaporphyrins, as well as in catalysis. Both procedures include cyanation reactions as the key steps. Magnesiation of cyanoferrocene, followed by reaction with electrophilic tosyl cyanide, affords the target compound in only two synthetic steps from ferrocene. In addition, 1,2-dicyanoferrocene can be prepared by a three step procedure, which implies a twofold cyanation of 1,2-dibromoferrocene, using Zn(CN)${}_{\mathrm{\text{2}}}$, in a biphasic medium and in the presence of bulky $t$-BuXPhos-Pd-G3.

While most of porphyrins and related macrocycles have been synthesized by classical acid-catalyzed condensation and oxidation reactions, nucleophilic aromatic substitution reactions have recently emerged as a new protocol to construct novel porphyrinoids. $\alpha \alpha \prime$-Dibromotripyrrin 3 was developed as a useful building block composed of three pyrrolic segments and two meso-carbons, which was allowed to react with various nucleophiles. Herein, we applied this strategy to synthesize carbaporphyrinoids containing two nitrogen atoms at the meso-positions. Reaction of $\alpha \alpha \prime$-dibromotripyrrin 3 with meta- and para-phenylenediamine gave diazabenziporphyrins 8 and 9in good yields. Their oxidized species 12 and 13 were generated by facile oxidation with lead dioxide. While diaza-meta-benziporphyrin 12 exhibited nonaromatic characteristics, diaza-para-benziporphyrin 13 was revealed to be aromatic in view of ${}^{\mathrm{\text{1}}}$H NMR, bond-alternation, and nucleus-independent-chemical-shift calculations. Curiously, aza-meta-benzicorrole 11 was obtained in a low yield by intramolecular cyclization reaction of $\alpha$-anilino-$\alpha \prime$-bromotripyrrin with potassium carbonate.

We synthetized and characterized a mono spermine porphyrin derivative by NMR, UV-vis and fluorescence spectroscopy. The photophysical properties and the protonation equilibria of 5-(4-carboxyphenylspermine)-10,15,20-triphenylporphyrin have been investigated, showing that porphyrin does not aggregate in acidic solutions, differently from what occurs as soon as the core of the porphyrin is deprotonated. These aggregation processes have been detected by the rising of new fluorescence band and a significant splitting of the Soret band.

The catalytic activity of the ruthenium(VI) bis-imido porphyrin complex/TBACl binary system in promoting the CO${}_{\mathrm{\text{2}}}$ cycloaddition to epoxides forming cyclic carbonates is here reported. The system was very efficient in catalyzing the conversion of differently substituted epoxides under mild experimental conditions (100 $deg$C and 0.6 MPa of CO${}_{\mathrm{\text{2}}})$. Even if the sole TBACl resulted active under the optimized experimental conditions, the addition of ruthenium species was fundamental to maximizing the reaction productivity both in terms of epoxide conversions and cyclic carbonate selectivities. A preliminary mechanistic study indicated a positive role of ruthenium imido nitrogen atom in activating carbon dioxide.

Examples of internally alkylated azuliporphyrins were prepared by MacDonald-type “3 + 1” condensations. 2-Methyl- and 2-ethylazulene reacted with an acetoxymethylpyrrole in the presence of an acid catalyst to give azulitripyrranes. Following cleavage of the terminal protective groups, condensation with a diformylpyrrole in the presence of hydrochloric acid and oxidation with ferric chloride afforded 21-alkylazuliporphyrins. An azulene dialdehyde similarly reacted with an $N$-methyltripyrrane to generate a 23-methylazuliporphyrin. The products could only be isolated in protonated form and the free-base internally alkylated azuliporphyrins proved to be unstable. Nevertheless, the dications are highly diatropic and the internal alkyl group resonances were shifted upfield to beyond -3 ppm. Reaction of a 23-methylazuliporphyrin with palladium(II) acetate primarily afforded a palladium(II) complex with loss of the internal methyl substituent. However, two palladium(II) benzocarbaporphyrins were also identified that were formed by sequential oxidative ring contraction and methyl group migration. Internally alkylated azuliporphyrins provide new insights into the reactivity of the system and the results show that the introduction of alkyl substituents within porphyrinoid cavities greatly modifies the properties of these structures.

Octa-substituted metallophthalocyanines [M = Ni(II), Zn(II), Co(II), and Cu(II)] carrying 3,4-dialkoxyphenyl tosylamino groups at the peripheral positions have been synthesized from 1,2-dicyano-4,5-bis[(3,4-dialkoxyphenyl-tosylamino)methyl]benzene in the presence of the corresponding anhydrous metal salt. Next to the metal ion center, the length of the alkyl chains in the dialkoxyphenyl moiety ($n=4$, 5, 6, and 12) was varied. In total, sixteen soluble phthalocyanines have been characterized by elemental analysis, FT-IR and ${}^{\mathrm{\text{1}}}$H-NMR spectroscopy as well as mass spectrometry. Furthermore, the gas sensing properties of these new compounds have been studied using quartz crystal microbalance transducers. The sensing properties are described on the basis of sensor responses to nine different test analytes comprising volatile organic compounds, toxic gases, and chemical warfare agent simulants. The influence of the metal ion center and substituents on sensor selectivity and sensitivity is discussed. The compounds show good performance in the gas-sensing experiments with diverse responses to the analytes. Phthalocyanine species with pronounced selectivity for polar analytes, hydrocarbons or amines have been identified among the set of sensors with the help of multivariate data exploration methods. The results reveal that quite a high diversity in terms of selectivity is introduced through the minute variations to the phthalocyanine structure.

Complexation of three (1$R$,2$R)$-2-aminocyclohexyl arylthioureas (aryl $=$ 3,5-bis(trifluoromethyl)phenyl; phenyl; 3,5-dimethylphenyl) as the guests to ZnTPP and ZnOEP hosts has been studied by means of UV-vis, CD spectroscopies and computational simulation. The complexation proceeds via coordination of the primary amino group to the zinc ion of the metalloporphyrin and induces a moderate circular dichroism signal in the Soret band of the porphyrins. The association constants increase with larger electron-withdrawing properties of the porphyrin host and larger electron-donating ability of the guest, indicating predominantly electrostatic (Lewis acid-base) character of the complexation. Computational study of the (1$R$,2$R)$-2-aminocyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea and ZnTPP complex revealed slight asymmetric distortion of the porphyrin plane caused by the chiral guest and additional $\pi$–$\pi$ interactions between the host and guest molecules. The calculated CD spectrum for the same system reproduces the experimentally observed one.

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 $\mathrm{ffl}$ 10${}^{\mathrm{\text{3}}}$–3.9 $\mathrm{ffl}$ 10${}^{\mathrm{\text{4}}}$ M${}^{\mathrm{\text{-1}}}$. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP${}^{+}$-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

The reactivity of porphyrin radical cationic species derived from octaethyl porphyrin (OEP) or meso-aryl porphyrins with nucleophiles, envisioned as an access route to elaborate porphyrin dimers, has been studied and optimized in the case of OEP. Standardized conditions have been applied to various spacers to show that the success of the reaction is mostly nucleophile dependent and that the method has little chances to yield non-linear bis-porphyrins.

Three BODIPYs bearing 1,3,5,7-tetramethyl substituents and a meso-8-aryl group were synthesized and investigated, both experimentally and computationally. The presence of the 1,7-methyl groups and of ortho-substituents on the meso-8-aryl ring prevent free rotation of the meso-8-aryl group, resulting in high fluorescence quantum yields. Substitution at the 2,6-positions of these BODIPYs with chlorine atoms causes pronounced red-shifted absorptions and emissions, and in the case of 2,6-dichloro-1,3,5,7-tetramethyl-8-(2,4,6-triphenylphenyl)-BODIPY 2c increases its fluorescence quantum yields to 0.93 in dichloromethane and 0.98 in toluene. The X-ray structure of 1,3,5,7-tetramethyl-8-(2,4,6-triphenylphenyl)-BODIPY shows increased deviation from planarity and smaller dihedral angle of the meso-8-aryl group compared with the meso-8-phenyl- and meso-8-mesityl-BODIPY analogs. The presence of 2,6-chlorine atoms was found to not significantly affect the rotational barriers of the meso-8-aryl-groups.

The indium(III) complexes of (4-(tert-butyl)phenyl)-substituted tetraazaisobacteriochlorin (TAiBC) and tetraazachlorin (TAC) were synthesized by direct template condensation of bis(4-(tert-butyl)phenyl)fumaronitrile and tetramethylsuccinonitrile using indium(III) ion as a matrix. The corresponding metal-free tetraazaisobacteriochlorin and tetraazachlorin were obtained by demetallation of their indium(III) complexes. These metal-free complexes were characterized using elemental analysis, mass-spectrometry, ¹H and ${}^{13}$C{¹H}NMR spectroscopy, UV-vis and MCD spectroscopy as well as DFT and TD-DFT calculations. Due to the low symmetry of the molecules, the NMR data were complex, but could be assigned by collecting 1D- and 2D NMR data and comparing with the results of quantum chemical calculations. From the position of the pyrrole proton signal (6.78 ppm), it was found that the diatropic current of TAiBC is much weaker than that of TAC, and plausibly the weakest among porphyrinoids so far reported. Absorption and MCD spectra were reasonably interpreted using the calculated absorption spectra.

Chlorin e6 (Ce6) and its derivatives are among the most important photosensitizers in photodynamic therapy. Due to their intense fluorescence, chlorins may also be used for diagnostics. However, low solubility in water and high tendency to aggregation restrict their medical use. Here we demonstrate that apo-myoglobin, by reinserting Ce6 in its heme binding pocket, can be used to monomolecularly disperse it. The reconstructed myoglobin-Ce6 adduct presents noticeable changes in the photophysical properties of the chromophore. A red-shift, in particular in the transparency window, can be observed in the absorption and in the emission spectra of the adduct compared to the spectra of the free chlorin in PBS. The adduct presents a higher quantum yield and an increased excited-state lifetime with respect to the free Ce6. The binding of Ce6 to apo-myoglobin determines a decrease of the ¹O₂ generation but a three-fold increase of peroxides production, determining globally an increase in the performance of Ce6 as a photosensitizer and imaging agent.

The electronic structures of a set of PcFe(azole)₂ complexes (azole = imidazole, $N$-methylimidazole, pyrazole, isoxazole, thiazole, 1,2,4-triazole, 3-amino-1,2,4,-triazole, and 5-amino-1,2,3,4-tetrazole) were examined by Mössbauer spectroscopy and Density Functional Theory (DFT) calculations. In addition, the geometric distortions in these compounds were elucidated by X-ray crystallography for imidazole, pyrazole, and thiazole-containing compounds. Predicted by DFT calculations, Mössbauer hyperfine parameters for all compounds are in reasonable agreement with experimental results, and the influence of the $\sigma$-donor and $\pi$-acceptor properties of the axial azoles on the electronic structure of the PcFe(azole)₂ complexes is demonstrated by comparison with the reference PcFePy₂ compound.

Optical absorption and emission, electrochemical, and photochemical properties of peripherally functionalized with flexible and rigid $\pi$-extended substituents on A₂ and A₂B₂ type zinc porphyrins is investigated. The significance of rigid $\pi$-substituents over flexible ones in governing the spectral properties is unraveled. Flexible $\pi$-substituents on the porphyrin ring caused appreciable spectral broadening compared to porphyrin carrying rigid $\pi$-substituents. Further, supramolecular dyads are formed by coordinating phenyl imidazole functionalized fullerene, C${}_{60}$Im. The calculated binding constants for the 1:1 complexes is in the order of 2–7 × 10⁵ M${}^{-1}$ suggesting stable complex formation. Free-energy calculations performed according to the Rehm–Weller approach suggested possibility of excited state electron transfer in these dyads. Femtosecond transient absorption studies of the dyads performed in $o$-dichlorobenzene showed evidence of occurrence of electron transfer from the singlet-excited state that was in competition with the intersystem crossing process to populate the triplet-excited state of porphyrins.

The aggregation properties of two peptide–porphyrin conjugates were investigated by optical spectroscopy and microscopy imaging with nanometer resolution. Specifically, a tetraphenylporphyrin platform was functionalized by (L)-magainin, a 23-residue long antimicrobial peptide, and by a (L)-magainin analogue differing from the parent peptide by a single residue substitution, $i.e.$ an Ala vs. Phe replacement in the position 5 of the peptide chain. Spectroscopic and microscopy results show that this single-site substitution has a small effect on the secondary structure attained by the two peptide analogues, but deeply affects the morphology of the mesoscopic structures deposited on hydrophilic mica from methanol/water solutions. In particular, only the Ala-substituted peptide-porphyrin conjugate was shown to be able to form micrometric fibrils, coating homogeneously a hydrophilic mica surface. These results pave the way for potential applications of porphyrin-peptide compounds in localized photodynamic therapy and for designing solid-state stereoselective sensors.

We present here a new type of fluoride ion optode, constituted by a highly lipophilic PVDF porous membrane modified with a liquid receptor layer containing the emission-active Si corrole F${}^{-}$ selective ionophore. For the optimized composition of the receptor layer, in acidic solutions an increase of Si-corrole emission was observed by increasing fluoride ion concentration, a behavior different from most porphyrinoid-based optical sensors. An observed linear dependence of the Si corrole emission intensity (read at 635 nm) was within the range 10${}^{-5}$ to 10${}^{-2}$ M of fluoride ions.

Three new covalently linked BODIPY-metal dipyrrin conjugates (Pd${}^{2+}$, Zn${}^{2+}$ and Re${}^{1+})$ were synthesized by treating $\beta$-dipyrrinyl BODIPY with appropriate metal salts in toluene in the presence of triethylamine at 120$deg$ C. The conjugates were isolated in decent yields either by recrystallization or by column chromatographic purification. The conjugates were thoroughly characterized by 1D and 2D NMR spectroscopy, absorption, cyclic voltammetry and DFT/TD-DFT studies. The studies revealed that the BODIPY and metal dipyrrin moieties in conjugates interact very weakly with each other and retain their individual characteristic features. The conjugates are electron deficient and non-fluorescent in nature.

Tetra-substituted zinc(II) and copper(II) phthalocyanines bearing peripheral alkoxy-monoterpene groups were prepared by conventional vs. non-conventional synthetic approaches (ultrasound and microwave irradiation). The synthesis of (1$R)$-(–)-myrtenol (a) and (1$R$,2$S$,5$R)$-($-)$-menthol (b) derived phthalonitrile precursors was performed through ipso-nitro aromatic substitution reactions, with optimal conditions being obtained using ultrasound irradiation, which allowed us to achieve full conversions in 4.5 h, with isolated yields up to 74%. The subsequent cyclotetramerization of monoterpene-based phthalonitriles was carried out using Zn(II) or Cu(II) salts as metal templates, and also using conventional and non-conventional heating methods. Microwave-assisted synthesis was shown to be the most efficient approach, providing complete conversions in 1 h, yielding the target monoterpene-based metallophthalocyanines in up to 70% isolated yields. Furthermore, photophysical and photochemical studies revealed that Zn(II) phthalocyanines possess fluorescence quantum yields in the range of ${\mathrm{\Phi }}_F=$ 0.27–0.29, while Cu(II) phthalocyanines exhibited room temperature phosphorescence. In addition, the monoterpene-based Zn(II) phthalocyanines led to high singlet oxygen quantum yields (${\mathrm{\Phi }}_{\mathrm{\Delta }}=$ 0.55–0.69).

Corrole molecules deposited from aqueous solution on Au(111) arrange flat forming mesa-like clusters (islands), as evidenced by in situ scanning tunneling microscopy (STM). A morphology quantitative assessment of the entire image is given by STM data analysis, evaluating the islands’ fractal dimension as a whole. To this end, two methods are employed: the first exploits the power law that binds the perimeter and the area of all the islands; the second is simply a value of an appropriate average of the fractal dimensions of the islands. In fact the two methods return very close results.

A low-cost on-paper sensor based on 5,10,15-tritolylcorrolatocobalt(III) triphenylphosphine, CoTTCorr(PPh₃), was developed for cyanide detection in aqueous solutions. The sensor was coupled to a smartphone and used a home-written color intensity analysis software in order to record and interpret the colorimetric response. The detection of cyanide was possible down to 0.053 mg/L, an order of magnitude lower than the value of 0.5 mg/L set by the World Health Organization (WHO) for safe short-term exposure of cyanide in potable water. The colorimetric sensor had selectivity toward cyanide ions over the anions Cl-, Br, F-, NO₂, SCN-, OA${}_{\mathrm{\text{c}}}$-,ClO₄-, H₂PO₄- and HCO₃- while the influence of NO₃- ions on the sensor optical response towards cyanide was overcome by optimization of the ionophore/anion-exchanger ratio inside the sensing material. The best performance was obtained for the optode with an ionophore to exchanger ratio of 1:3. The optimized optodes were employed for quantification of cyanide content added to potable water and saliva.

A 2,6-diiodo-3,5-dithienylvinyleneBODIPY dye was prepared and encapsulated with folate-chitosan capped Pluronic${}^{\circledR }$ F-127 to provide drug delivery systems for photodynamic therapy (PDT). Moderately enhanced singlet oxygen quantum yields were observed for the dye encapsulation complexes in water. The in vitro dark cytotoxicity and photodynamic activity were investigated on the human breast adenocarcinoma (MCF-7) cell line. Minimal dark cytotoxicity was observed for the BODIPY dyes in 5% DMSO and when encapsulated in folate-functionalized chitosan-coated Pluronic${}^{\circledR }$ F-127 micelles, since the cell viability values are consistently greater than 80% over the 0-40 $\mu \mathrm{\text{g}}\cdot {\mathrm{\text{mL}}}^{-1}$ concentration range. Upon irradiation of the samples, significant cytocidal activity was observed for the encapsulation complex of a 2,6-diiodo-8-dimethylaminophenyl-3,5-dithienylvinyleneBODIPY dye with less than 50% viable cells observed at concentrations $\ge 20\mu \mathrm{\text{g}}\cdot {\mathrm{\text{mL}}}^{-1}$.

Meso-tetrapyrenylporphyrin and its metal (Co${}^{\text{II}}$, Cu${}^{\text{II}}$, Ni${}^{\text{II}}$ and Zn${}^{\text{II}}$) complexes were synthesized, characterized and studied for their spectral, electrochemical and energy transfer properties. DFT optimization was carried out to gain an insight into the interactions between the porphyrin $\pi$-system and the pyrenyl substituents. The pyrenyl substituents and the porphyrin core remain essentially orthogonal to each other in both the free base and the metallated porphyrins. Redox potentials of the pyrenylporphyrins are marginally shifted as compared to their corresponding phenyl derivatives. Förster resonance energy transfer (FRET) studies were carried out in toluene for free-base pyrenylporphyrin and its Zn(II) complex. Since pyrene is a good donor, an efficient energy transfer from pyrene (D) to the porphyrin core (A) on the order of 80–85% was observed for these two compounds. It was observed that energy transfer occurs mainly via ”through-bond” (TB) interaction rather than ”through-space” (TS) interaction.