Journal of Porphyrins and Phthalocyanines

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.

By using density functional theory with (DFT) with functional M06 and the def2TZVP basis set, combining D3 version of Grimme’s dispersion, the molecular structures of [18]porphyrin-(1.1.1.1) (porphyrin) and five its structural isomers, namely [18]porphyrin-(2.0.2.0) (porphycene), [18]-porphyrin-(2.1.0.1) (corphycene), [18]porphyrin-(2.1.1.0) (hemiporphycene), [18]porphyrin-(3.0.1.0) (isoporphycene), and “N-confused” porphyrin, were calculated. The values of the most important bond lengths, bond and non-bond angles in these compounds, and NBO analysis data are presented. It was noted that In almost all of these isomers, both the groups of four nitrogen atoms and the 16-membered macrocycles that contain these atoms are coplanar; the only exception is N-confused porphyrin, which has a small deviation from coplanarity (0.8${}^{\circ }$ and 5.1${}^{\circ }$, respectively). The interatomic distances between adjacent nitrogen atoms in porphyrin are identical, in porphycene, they are equal in pairs, in corphycene, two are equal to each other; the rest are different, and in the remaining isomers, all four are different. NBO analysis of all the above isomers was carried out, and based on the data, a high degree of delocalization of the electron density in these compounds was stated. The values of the standard enthalpy ${\mathrm{\Delta }}_f{H}^0$, entropy $S_f^0$ and Gibbs energy ${\mathrm{\Delta }}_f{G}^0$ of formation, and the total energies of these compounds were also calculated. Based on these data, it was concluded that the most stable isomer is porphyrin, Porphycene is slightly less stable, while the stability of the other isomers is significantly lower, and isoporphycene has the lowest stability (and, accordingly, the highest values of ${\mathrm{\Delta }}_f{G}^0$ and relative total energy $\mathrm{\Delta }E)$.

A class of novel quinoxalinochlorin compounds bearing different substituents at quinoxaline ring used as photosensitizers for photodynamic therapy (PDT) were designed and synthesized along with the optimization of the reaction conditions of the last reduction step. The UV-visible spectra of these compounds displayed a chlorin-characteristically sharp Q${}_{IV}$ band (the fourth Q-band at the longest wavelength) but significantly red-shifted (${\lambda }_{max}$ > 687 nm). The fluorescence emission spectra also experienced a significant red-shift. The fluorescence and singlet oxygen quantum yields were measured using zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP) as a standard (${\mathrm{\Phi }}_f$ = 0.033 and ${\mathrm{\Phi }}_{\mathrm{\Delta }}$ = 0.73 in toluene). All the quinoxalinochlorin compounds reported showed good photostability and those compounds bearing substituent with electron-donating conjugated effect at quinoxaline ring could produce high yield of singlet oxygen under light.

The modification of biomolecules is significant to chemical biology. One of the challenges is improving the trans-membrane transport, and recently vitamin B${}_{12}$ has emerged as a biocompatible transporter that can facilitate the uptake. This study investigates the formation of adducts between vitamin B${}_{12}$ thiolate and 5HP2O linkers (5-hydroxy-1,5-dihydro-2$H$-pyrrol-2-ones) as a novel approach to converting native B${}_{12}$ into versatile bioconjugation-ready intermediates. We synthesized two model 5HP2O linkers and optimized the reaction with the readily available and bench-stable isothiouronium salt of vitamin B${}_{12}$ that generates reactive thiolate in situ. The optimal conditions included using a 1:1 mixture of H₂O/EtOH or H₂O/DMSO as solvents, excess of 5HP2O, and methylamine, at the concentration of 3.5 mM. This work enriches the bioconjugation toolkit and offers new insights into the development of vitamin B${}_{12}$-containing therapeutics.

Various kinds of Michael acceptors could be introduced at the C13²-position in an epimeric mixture of methyl pheophorbides-$a$/$a$’ under basic conditions. The isolated yields and C13²-epimeric ratios ($R$/$S$ > 1) of the adducts depended on the electron-withdrawing group in the Michael acceptors. Some Michael acceptors possessing a less electron-withdrawing group could not react with methyl pheophorbides-$a$/$a$’. Neither $\alpha$- nor $\beta$-substituted Michael acceptors gave the desired products. On the other hand, a Michael acceptor possessing a terminal alkyne was introduced as the C13²-alkenyl moiety. We here report the scope and limitations of the Michael addition reactions for chlorophyll-$a$ derivatives.

The sensitizer is one of the key components in achieving the high efficiency and durability of a dye-sensitized solar cell (DSSC) device. The porphyrin class of sensitizers using the donor-$\pi$-acceptor concept with either I${}^{-}$/I${}_3^{-}$ or Co(II/III) redox couples have demonstrated device efficiency >10%. The sensitizer with triphenylimidazole donor and and 3-(5(benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2yl)-2-cyanoacrylic acid as an acceptor (LG18) have illustrated device efficiency of 10.51%. In this report, we adopted femtosecond transient absorption (fs-TA) spectroscopy to explore the ensuing relaxation properties of LG18 and adsorbed on TiO₂ in solution upon 400 nm photoexcitation. Comparative analysis of the obtained TA data matrices of LG18 and LG18–TiO₂ samples confirms an ultrafast hot electron extraction (<150 fs, >k${}_{\text{EE}}$ = 6.5 × 10${}^{12}$ s${}^{-1})$ along with multi-step electron injection occurs from different excited states of LG18 with rate constant (k${}_{\text{ET}})$ in the range of 6.7 × 10${}^{11}$ s${}^{-1}$ to 5 × 10⁸ s${}^{-1}$ which are 3-4 order higher than charge recombination rate (k${}_{\text{rec}}$ $\sim$<1 × 10⁸ s${}^{-1})$.

The optical limiting properties of a 1,7-dithien-3-yl-3,5-di-4-hydroxyphenyl-azaBODIPY dye and its silver nanoparticle (AgNP) conjugate on the nanosecond timescale at 532 nm are reported. The photophysicochemical properties are compared to those of the parent 1,3,5,7-tetraphenylazaBODIPY complex. The thien-3-yl rings at the distal positions facilitate conjugation to AgNPs through the Ag-S interaction and a significant red shift of the main azaBODIPY spectral band. Favorable optical limiting properties are obtained that suggest 1,3,5,7-tetraarylazaBODIPYs and their nanoparticle conjugates merit further in-depth study in this context. This is further enhanced by conjugation to AgNPs.

A comparison of the chemistry of the tetraruthenated zinctetrapyridilporphyrin and zinctetrapyridylporphyrazine species has been performed, aiming to improve the understanding of the electronic coupling (or back-bonding) between the macrocyclic center and the peripheral [Ru(bipy)₂Cl]${}^{+}$ complexes. In the case of the supramolecular tetrapyridylporphyrins, the bridging pyridyl groups are located at the meso-carbon position so that their rotational properties decrease the electronic coupling between the peripheral complexes and the porphyrin center. However, in the tetrapyridylporphyrazine system, the interaction with $\pi$-backbonding Ru(II) complexes is greatly enhanced because the pyridyl groups are fused into the macrocyclic ring with stronger electron acceptor properties. Consequently, the fluorescence emission from the porphyrazine center can be directly pumped from the peripheral complexes by exciting in the Ru${}^{\text{II}}\to$ZnTPyPz($\pi$*) MLCT band, in contrast with the analogous porphyrin species. The electrochemical behavior of the ZnTRuPyPz complex exhibits the characteristic redox waves of [Ru${}^{\text{III}/\text{II}}$(bipy)₂Cl] at 1.00 V, showing a 0.080 V increase in comparison with the ZnTRuPyP complex, consistent with stronger $\pi$-back bonding interactions with the porphyrazine center. This observation was also corroborated by the pronounced spectroelectrochemical changes in the porphyrazine Q bands induced by the oxidation of the peripheral ruthenium complexes to Ru(III). The spectroscopic and electrochemical results indicate that the porphyrazines can be better than the porphyrins for developing electronically conjugated supramolecular systems.

Using aerobic conditions, a hitherto unknown N-confused bilatrienone analog (1-o) was synthesized through the metal-induced oxidative rearrangement of the N-confused bilatriene (1). The resulting metal complexes (Pd1-o; M = Pd and Pt1-o; M = Pt) were characterized by NMR spectroscopies, mass spectrometry, and single crystal X-ray diffraction analysis, showing the regioselective oxygenation and 2,3-shift of the methylene linkage of the terminal indole moiety. Due to the helically $\pi$-conjugated structure of the complexes, Pd1-o and Pt1-o, uniquely intense absorption bands in the near-infrared (NIR) region have emerged, respectively, which were assigned to be HOMO-LUMO transitions based on the time-dependent DFT calculations. Along with the non-emissive nature of the complexes, the efficient photothermal conversion capabilities were demonstrated in the toluene solution. Therefore, these complexes could potentially be used in photothermal therapies for biological tissues.

By using density functional theory with (DFT) with functional M06 and the def2TZVP basis set, combining D3 version of Grimme’s dispersion, the parameters of molecular structures (the values of the most important bond lengths, bond and non-bond angles) and thermodynamical characteristics (standard enthalpy ${\mathrm{\Delta }}_f{H}^0$, entropy $S_f^0$ and Gibbs energy ${\mathrm{\Delta }}_f{G}^0$ of formation) of six “N-confused” porphyrin structural isomers, which differ from each other by the different arrangement of the nitrogen atom on the outer “rim” (2N-, 5N-, 7N-, 8N-, 10N- and 12N-), were calculated. It is noted that the most stable of these isomers, contrary to expectations, is not the “2N-confused” porphyrin described in the literature, but the “12N-confused” porphyrin, which is still unknown in the experiment; the least stable is “5N-confused” porphyrin (5-aza-21-carbaporphyrin). The difference in the total energy values ??between the least and most stable structural isomers of “N-confused” porphyrin is about 30 kJ/mol, which is significant for this type of isomerism. It was noted that in all these isomers, both the groups of four nitrogen atoms and the 16-membered macrocycles that include these atoms are not strictly coplanar, and for each of them, at least a small deviation from coplanarity is observed, lying in the ranges of (0.1–0.3)${}^{\circ }$ and (0.5–1.5)${}^{\circ }$, respectively. In the molecular structures of all these compounds, there are no symmetry elements, so each of them belongs to the $C_1$ symmetry group; however, their electric dipole moments ($\mu$ ) are not very significant for such a low level of symmetry (as a rule, lesser than 3 Debye units). NBO analysis of all the above isomers was carried out, too; based on its data, a high degree of delocalization of the electron density in these compounds was stated.

Magnetic circular dichroism (MCD) and UV-Vis-NIR spectroscopy were used to investigate the spectroscopic signatures of the triplet-multiplet and other transitions observed in the simplest $d^9$ (Pc^tBuCu and Pc^(SO3Na)4Cu) and $d^1$ (Pc^tBuV=O and TPz^(OAr)8V=O) phthalocyanine systems. Density Functional Theory (DFT) and time-dependent DFT (TDDFT) calculations allowed accurate correlation between the experimental and theoretical data. In particular, similarities between vibronic profiles in Q-band and triplet-multiplet band regions as well as the presence of MCD $A$-terms associated with the 0-0 transitions support the relationship between the Q- and triplet-multiplet transitions.

Mono $\beta$-acetamide appended porphyrins, MTPP(NHCOMe) (M = 2H, Zn^II, Cu^II, Ni^II, Co^II, Mn^III and V^IV, TPP = meso-tetraphenylporphyrin) were synthesized and characterized by various spectroscopic techniques. The effect of the $\beta$-substituents and core metal ions on the electronic spectra was evaluated. The free base and Zn^II porphyrins exhibited weak emission and a lower singlet state lifetime than H₂TPP and ZnTPP. The first ring reduction potential of MTPP(NHCOMe) (M = Co^II, Ni^II, Cu^II, Zn^II, V^IV porphyrins exhibited a 10-70 mV cathodic shift whereas, free base and Mn^III derivatives showed 10-100 mV anodic shift than corresponding MTPPs. The slightly saddled-shaped structures of CuTPP(NHCOMe), ZnTPP(NHCOMe), and Mn(Cl)TPP(NHCOMe) were confirmed by the single crystal X-ray diffraction analysis. Density functional theory (DFT) studies revealed that the NiTPP(NHCOMe) has the highest average deviation of the 24-core atom from the mean porphyrin plane, $\mathrm{\Delta }$24 (± 0.278 Å) and the average displacement of $\beta$-pyrrole carbons from the porphyrin mean plane, $\mathrm{\Delta }$C${}_{\beta }$ (± 0.278 Å) values among all the synthesized porphyrins. The HOMO-LUMO gap observed from DFT and Cyclic voltammetry studies are qualitatively comparable. The EPR spectroscopy confirmed the +4 oxidation state of the vanadyl ion, exhibited by the comparable eight-line pattern.

Michl’s 4N+2 perimeter model is used to analyze trends in the optical spectra and electronic structures of a series of free base porphyrin model ligands to identify key structure-property relationships associated with the N- and neo-confusion, and the introduction of reduced pyrrole and direct pyrrole-pyrrole bonds to the porphyrin ligand. Following Michl’s predictions, the calculated Q band intensities at the CAM-B3LYP/6-31G(d) are found to correlate with $|\mathrm{\Delta }$HOMO² – $\mathrm{\Delta }$LUMO${}^2|$, where $\mathrm{\Delta }$HOMO and $\mathrm{\Delta }$LUMO refer to the energy gaps between the MOs arising from the frontier occupied and unoccupied MOs with M_L = ± 4, ± 5 angular nodal patterns, but only when dyes with the same parent hydrocarbon perimeter is involved. Corrole analogues such as N-confused corroles and C-fused norroles are predicted to have the most intense Q bands, which is inconsistent with what has been observed experimentally. Combining N- and neo-confusion with the reduction of peripheral pyrrole bonds in the context of chlorins and bacteriochlorins does not appear to result in more favorable properties for biomedical singlet oxygen photosensitizer applications.

Herein, we report the synthesis of cobalt-coordinated β-β’ bicyclo[2.2.2]octadiene-fused corrole 1-Co and benzo-fused 2-Co with axial PPh₃ ligands. The structures and properties of 1-Co and 2-Co are fully studied via single-crystal X-ray diffraction, UV-Vis spectroscopy, cyclic voltammograms, and density functional theory calculations. The benzo-fusion of 2-Co leads to a reduced energy gap and distinct coordination, photophysical, and redox properties. Compared to 1-Co, 2-Co exhibits increased bond-length alternation, red-shifted UV-vis absorption bands, and decreased aromaticity. For 2-Co, the axial PPh₃ dissociates during both oxidation and reduction processes, but for 1-Co, the dissociation occurs only during reduction. The theoretical calculations further predict a low-lying open-shell singlet state for 2-Co. This study advances the functionalization strategy of cobalt corroles for a broader range of potential applications.

Near-infrared absorbing azaborondipyrromethenes (azaBODIPYs), 1, 2, and 3, tethered with phenothiazine (PTZ) and/or naphthalene at 1,7 and/or 3,5 positions, were synthesized and photoinduced energy (PEnT) and electron (PET) events occurring within these compounds were systematically studied. Steady-state fluorescence studies have shown that, when the phenothiazine moiety, in 1 and 2, was selectively excited, the fluorescence of the PTZ and azaBODIPY was quenched, indicating the occurrence of PET from the singlet excited phenothiazine to the azaBODIPY. On the other hand, when the naphthalene moiety in 3 was excited, the emission of the naphthalene was observed to be quenched with the concomitant appearance of the azaBODIPY emission indicating the display of PEnT from ¹naphthalene* to the azaBODIPY. Interestingly, in the case of 1, selective excitation of naphthalene resulted in the quenching of both the naphthalene and azaBODIPY emissions, indicating the possibility of PEnT from ¹naphthalene* to azaBODIPY followed by a tandem PET from the ground state of the phenothiazine moiety to the azaBODIPY. The present work showed the synthetic scope of introducing two different chromophores onto the azaBODIPY platform to produce panchromatic dyes and systematically revealed the significance of the individual constituents, PTZ and naphthalene as electron and energy donors, and azaBODIPY as an excited state energy or electron receiver in the PET and PEnT processes.

Heme-type porphyrins can become distorted depending on their environment, altering their chemical and electronic properties. While trends have been established for several ruffle-distorted porphyrins, their research on synthetic models of heme-type porphyrins is limited. We identified a dynamic process on the ruffled porphyrin bis(2-methylpyridinato)iron(III)-Protoporphyrin-IX (2) that does not exist in bis(pyridinato)iron(III)-Protoporphyrin-IX (1). We modeled these molecules as {OMP(2-CH₃Py)₂Fe}${}^{+}$ and {[OMP](Py)₂Fe}${}^{+}$ respectively. Geometry optimization using density functional theory (DFT) suggests the ruffled conformation of 2 (angle $\overline{x}$ of -29.7°) and the planar conformation of 1. The calculated electron affinity and ionization potential vary depending upon ruffling. The calculated 0.253 eV difference in electron affinity and the 0.223 eV in ionization potential indicate that the reduction of the planar structure has a higher energy requirement than the ruffled-distorted structure but has a lower energy requirement for its oxidation. We found that these energy differences are not solely attributed to the distortion of the macrocycle. The difference is linked to the interaction between the d_xy orbital and the HOMO-1 3a_2u, allowed by symmetry when a porphyrin ring has a ruffled conformation stabilizing the frontier orbitals, thus making the oxidation process have a higher energy barrier. On the other hand, the reduction process is facilitated by the interaction of metal d${}_{\pi }$ orbitals with the porphyrin 4e. These highlight the distinct differences between the ruffled and the planar conformations.

A series of phosphorus(V) porphyrins functionalized with meso-phenyl, tolyl, or 4-methoxyphenyl groups and axial-ethoxy, trifluoroethoxy, or ethylene glycoxy groups have been synthesized and their spectroscopic, redox, and optical properties were investigated. The X-ray crystal structures revealed a significant saddling in porphyrin molecular structures due to the presence of a small P(+5) ion in the cavity. The absorption and fluorescence properties are less sensitive to the meso-functionality, with small redshifts observed when moving from phenyl to tolyl and then to 4-methoxyphenyl on the phosphorus(V) porphyrin. In contrast, the meso- and axial-functionalities significantly influenced the redox properties. Specifically, the meso-4-methoxy phenyl group lowered the oxidation potentials, while the axial trifluoroethoxy units reduced the reduction potentials. This study demonstrates that by carefully choosing the axial and meso-substitutions, it is possible to selectively tune the redox potentials with minimal impact on optical properties. Steady-state and time-resolved measurements revealed relatively high fluorescence quantum yields, with lifetimes ranging from 2 to 4 ns. Together, the high fluorescence quantum yields and tunable redox potentials suggest that the investigated porphyrins could serve as excellent photosensitizers in model compounds for artificial photosynthesis and molecular electronic and photonic devices.

Size-selective synthesis of calixpyrrole-related macrocycles remains challenging, particularly for ring-contracted and expanded analogues, although calix[4]-type macrocycles are often obtained as major products via conventional acid-catalyzed condensation reactions of aryl monomers. Here, we found that the strain-based design of thiazole-containing macrocycles enables the size-selective synthesis of calix[$n$]furan[2$n$]thiazoles ($n$ = 1 or 2) in which two thiazole units are linked by a methylene bridge. The DFT calculation through StrainViz analysis revealed that calix[1]furan[2]thiazole bearing a methylene bridge had a total strain of 11.2 kcal/mol, which was smaller than that of calix[3]pyrrole (13.4 kcal/mol). The target calix[1]furan[2]thiazole was almost exclusively formed in 45% yield by a Hantzsch reaction between the corresponding bis($\alpha$-bromoketone) and bis(thioamide) at 0.50 mM concentration. When the substrate concentration was increased above 10 mM, the calix[6]-type product, calix[2]furan[4]thiazole, was formed as the major product. Despite the existence of the meso-CH₂-bridge, the obtained macrocycles were stable to air oxidation. Acid-catalyzed hydrolysis of the furan rings in calix[1]furan[2]thiazole and subsequent Paal–Knorr reaction afforded calix[1]pyrrole[2]thiazole. We also found that the deformation angles $\alpha$ determined from the single crystal X-ray structures show a good correlation with the total strain and synthetic yield of calix[3]-type compounds via direct macrocyclization.

The synthesis of new Zn(II), and Si(IV) phthalocyanine (Pc) derivatives containing chalcone group was successfully achieved and the compounds were characterized by MALDI-TOF mass spectroscopy, FT-IR, ¹H NMR, ${}^{13}$C NMR, and UV-vis spectral data. The photophysical and photochemical properties of these novel Pcs were investigated in DMF. The in vitro cytotoxic effect of the compounds on mammary breast adenocarcinoma cell lines (MCF-7 and MDA-MB-231) and normal mammary breast epithelium (MCF-12A) were evaluated by using the WST assay. Based on the WST assay analysis, cytotoxicity of the Pc derivatives to mammary breast carcinoma cells was compared to normal mammary breast epithelium cells dependent on light illumination. The results of the present investigation demonstrate that all the Pc derivatives containing the chalcone group have a phototoxic effect on mammary breast cancer cells and could be promising photodynamic therapy (PDT) agents for further studies.

Protonation studies were conducted on $\beta$,$\beta$'-fused 2,7,12,17-tetraisopropyldinaphthoporphycene and 2,3,6,7,12,13,16,17-octaethylporphycene with trifluoroacetic acid and pentafluorobenzoic acid. The weaker pentafluorobenzoic acid was able to form a stable diprotonated species with dinaphthoporphycene only in the solid state, owing to the $\pi$-$\pi$ stacking interactions.

Deprotonated meso-hydroxyporphyrin Au^III complex, acting as a zwitterion, was synthesized. In the solid state, the zwitterionic porphyrin formed a stacked columnar structure through dipole–dipole and $\pi$–$\pi$ interactions. Energy decomposition analysis revealed that favorable dispersion forces were the primary contributors to the interactions between stacked zwitterionic porphyrin units. Furthermore, the solution-state absorption spectra of the zwitterionic porphyrin were influenced by the polarized structure, whereas the solid-state absorption spectra were associated with the packing arrangement.

To achieve the high charge carrier mobility of small molecular organic semiconductors, a molecular design strategy for controlling the packing structure of two-dimensional (2D) $\pi$-extended organic semiconductors in single crystal is essential. Although tetrabenzoporphyrin (BP) is one of the promising organic semiconductors, the control of the packing structure is still challenging. To improve the low solubility of 5,15-bis(trimethylsilylethynyl)-tetrabenzoporphyrin (TMS-BP) and the crystal polymorph of 5,15-bis(triisopropylsilylethynyl)-tetrabenzoporphyrin (TIPS-BP), 5-triisopropylsilylethynyl-15-trimethylsilylethynyl-tetrabenzoporphyrin (TIPS-TMS-BP) with different substituents at meso-positions was synthesized. TIPS-TMS-BP gave a herringbone structure of antiparallel slipped-stack dimers in single crystals. The single crystal field effect transistors exhibit a high hole mobility of 1.65 cm² V${}^{-1}$ s${}^{-1}$ in parallel to $\pi$–$\pi$ stacking direction and moderate 0.37 cm² V${}^{-1}$ s${}^{-1}$ in perpendicular to $\pi$–$\pi$ stacking direction.

A series of $\alpha$-nitro BODIPY dyes were obtained in moderate to high yields using cupric nitrate or nitronium tetrafluoroborate. Both methods allow for the regioselective electrophilic aromatic nitration of the pyrrolic positions under mild conditions, providing a series of $\alpha$-nitro BODIPYs in 30–85% yields. These novel dyes were fully characterized by NMR spectroscopy and HRMS. The photophysical properties of these BODIPYs were analyzed using UV-Vis, fluorescence spectroscopy and DFT calculations. The introduction of the nitro group led to notable redshifts in the absorption and emission bands, decreasing in molar absorptivity, and a reduction in fluorescence quantum yields of these BODIPYs. Furthermore, the electron-withdrawing character of the nitro substituent induces reduced HOMO and LUMO energy levels. In addition, representative transformation experiments, such as conversion to amines, were performed to investigate potential applications of these novel $\alpha$-nitro BODIPY dyes.

Two series of oxovanadium N-confused porphyrins (NCPs) were synthesized and characterized using HRMS, UV-Vis, IR, and EPR spectroscopy. The free-base NCPs [CTPPH]H₂ (1a) and [MeCTPP$H$]H (1b) reacted with VO(acac)₂ in DMF to form oxovanadium complexes [VO($H$CTPP)] (2a) and [VO(MeCTPP)] (2b). Oxidation of [VO($H$CTPP)] (2a) with meta-chloroperbenzoic acid ($m$CPBA) or iodosobenzene (PhIO) yielded [VO($H$CTPPO)] (3a) and [VO(CTPPOMe)] (4a), respectively, illustrating a substituent exchange on the inner carbon. In contrast, [VO(MeCTPP)] (2b) produced a single oxidized product, [VO(MeCTPPO)] (3b), regardless of the oxidant. X-ray crystallography revealed that 2a adopted a 2H tautomeric form, while 4a exhibited a 3H tautomeric form. EPR spectroscopy confirmed the V(IV) oxidation state in all complexes. Formation of 2a and 2b induced redshifts in the Soret band, while oxygen insertion in 3a and 3b caused further bathochromic shifts and Soret band splitting. The catalytic activity of these oxovanadium NCPs was evaluated for cyclohexene and thioanisole oxidation using H₂O₂ in CH₃CN. Cyclohexene oxidation at 60${}^{\circ }$C for 8 hours yielded 2-cyclohexen-1-one and cyclohexane-1,2-diol, while thioanisole oxidation at room temperature for 24 hours produced sulfone. An oxidoperoxidovanadium(V) intermediate was identified via ESI-MS. Notably, 3b and 4a exhibited turnover frequencies (TOFs) of 5.25–6.84 h${}^{-}$1 for cyclohexene oxidation, while all complexes showed TOFs of 3.09–4.17 h${}^{-}$1 for sulfur oxidation. This study highlights the structural and catalytic versatility of oxovanadium NCPs.

We report a mechanochemical method for synthesizing freebase corroles via the reaction of pyrrole with substituted benzaldehyde precursors. The study emphasizes the one-pot cryo-mechanochemical synthesis of 5,10,15-Tris-(TIPS-ethynyl)corrole (A₃-TIPS-ethynylcorrole) and 5,10,15,20-Tetrakis-(TIPS-ethynyl)porphyrin (A₄-TIPS-ethynylporphyrin) through ball-milling condensation. Subsequent oxidation with $p$-chloranil produced freebase corroles and porphyrins with yields of 40% to 70%, representing nearly a threefold increase over the previously developed MeOH/H₂O-based approach. Quantitative metalation of these freebase compounds was achieved in the ball mill at elevated temperatures. This method also improved the EcoScale values and significantly reduced the E-factor, highlighting its environmental benefits compared to traditional synthesis techniques.

A comprehensive Scanning Tunneling Microscopy (STM)-driven ab initio investigation was conducted to explore the effects of peripheral substitution and central metalation on the molecular self-assembly of phthalocyanines on highly oriented pyrolytic graphite (HOPG). This study reports, for the first time, the self-assembly behavior of phthalocyanines with phenoxy and ethoxy substitutions and Co and Mg as central metals. Through periodic boundary simulations, we demonstrate that the peripheral substitutions significantly influence the energetic stability and monolayer structure, while central metal variations play a minor role. Our findings suggest that phthalocyanines with identical peripheral substitutions exhibit similar unit cell structures on Highly Oriented Pyrolytic Graphite (HOPG), regardless of the central metal. Furthermore, while substituent positional isomerism does not significantly impact the adsorption energy, the orientation of the peripheral substituents critically affects intermolecular interactions, influencing the stability of the monolayers. The study also reveals that octa-substituted phthalocyanines, such as H₂Pc(OPh)₈, form more stable, well-packed monolayers compared to tetra-substituted derivatives, like H₂Pc(OEt)₄, which exhibit phase segregation and disorder. Additionally, solvent molecules such as phenyl octane (PhOct) stabilize the disordered H₂Pc(OEt)₄ monolayers by filling cavities between molecules. These results offer valuable insights into the design principles for engineering stable phthalocyanine monolayers, contributing to advancements in surface chemistry and materials science.

Understanding the crystal-packing patterns of tetrapyrroles underpins a number of objectives in materials sciences. Here, the zinc chelate of 3,13-diacetyl-10-(pentafluorophenyl)-18,18-dimethylchlorin was prepared, crystallized in the presence of tetrahydrofuran (THF), and analyzed by single-crystal x-ray diffraction (SCXRD). The zinc chlorin (Zn1) afforded a herringbone pattern of parallel columnar stacks of chlorins rotated by 67.41${}^{\circ }$ with respect to each other. The chlorins within a column are stacked in pairs having interplanar distances of 3.289 Å within a pair and 4.407 Å between pairs. The chlorins in a pair are aligned in a “head-to-head” arrangement with cofacial $\pi$–$\pi$ overlap chiefly only of the respective ring A units; the overall composition is thus of columnar stacks of slipped-stacked pairs of chlorins. Each chlorin is enantiomeric due to the coordination at the Zn(II) center of a single THF molecule; the juxtaposition of chlorin $\alpha$–$\beta$ faces opposite the apically ligated THF molecules affords a racemate. All chlorins in a column face in the same direction, with 3,13-acetyl groups essentially coplanar with the macrocycle and oriented toward the respective 5,15-positions (affording an O$\cdot \cdot \cdot$H–C contact of 2.33 or 2.39 Å), and with interdigitation of alternating pentafluorophenyl groups in adjacent columns. A large number of SCXRD analyses of synthetic chlorins will likely be required to understand the relationship between structure and assembly patterns.

A simple pyrrole-based Schiff base ligand, 2-[(2-pyrrolylmethylene)amino]phenol was used to synthesize a unique tetra palladium(II) complex by treating it with PdCl₂ in CH₃OH/CH₃CN for 1 h at room temperature. X-ray structure showed that each Pd(II) ion adopted a distorted square pyramidal structure and bonded to pyrrole “N”, imine “N”, two phenolate “O”s, and one Pd(II) ion with direct Pd(II)-Pd(II) bond. Three ligands are involved in completing the square pyramidal geometry of each Pd(II) ion and the structure appeared as a hashtag symbol and four Pd(II) ions formed a plus symbol within the hashtag structure. The tetra palladium (II) complex showed a very simple NMR spectrum and absorbs strongly in the UV-visible region.

A mild and efficient method for the acid-promoted demetallation of functionalized metalloporphyrins is described. In contrast to the normally harsh conditions required, a variety of Cu porphyrins were rapidly demetallated in excellent yields using methanesulfonic acid in a chlorinated hydrocarbon solvent at room temperature or under microwave heating. Some Co, Ni, and Ag porphyrins could also be efficiently demetallated. Notably, the presence of a small amount of a coordinating solvent in the reaction mixture either completely inhibited the demetallation or significantly slowed it down. Electron withdrawing functionality also slowed down the demetallation time.

In this study, we investigate the synthesis of spirofluorenyl-fused porphodimethenes through the reaction of the corresponding dipyrromethane with cycloheptyl-fused dipyrromethane and benzaldehyde under acidic conditions and subsequent oxidation. This yields a mixture of the expected 5,15-porphodimethenes, along with 5,10-porphodimethenes and tetraphenylporphyrin. These unexpected products are derived from the scrambling side reactions of the 9-fluorenyl-fused dipyrromethane, whose reproducibility was also demonstrated by the reaction of 9-fluorenyl-fused dipyrromethane and benzaldehyde. The mixture of 5,10-porphodimethenes and tetraphenylporphyrin could not be separated owing to their insufficient solubility in common solvents used for the chromatography and similar mobility on silica gel. The structural determination and final elucidation of each by-product were performed using X-ray crystal structure analysis by selecting single crystals from the crude crystallization systems. Such a procedure to synthesize 5,10-porphodimethenes can function as a protocol that can also be used to synthesize cyclic congeners of tripyrrins based on their fully conjugated tripyrrolic partial structures.