Expanded Porphyrins Research Articles

The effect of metal-to-ligand charge transfer on linear and nonlinear optical properties of hexaphyrin and metallo-hexaphyrins

Charge transfer from metal to ligand has implications in various fields of chemistry, physics and biology. The manipulation of spin properties would be necessary for controlling charge transfer in spintronics and biological applications. Upon binding to the metal atoms (Ni, Cu, Au, etc.), the spin properties would be modulated in organic conjugated molecules of less intrinsic spin–orbit coupling (SOC) due to SOC coming from the heavy elements. Emission spectra calculation is necessary to validate them as suitable fluorescence quenchers. The nonlinear optical properties like first-order hyperpolarisability β and second-order hyperpolarisability γ calculations are important to find out their relation between fluorescence quenching and higher order nonlinear optical (NLO) properties. From the second-order NLO properties, we computed degenerate four-wave mixing (DFWM) component ( γ ( 2 ) ( − ω ; ω , ω , − ω )) and finally quadratic nonlinear refractive indices of the expanded porphyrins (EPs). How the linear and nonlinear optical properties are dependent on the SOC coming from the heavy materials (Ni, Cu, Au), and charge transfer process is the most interesting question to be addressed for their potential uses for various optoelectronic and spintronic applications.

Controlling the CO2 Reduction Reaction through Dual‐Atom Catalysts Embedded in Expanded Porphyrins: A DFT Study

In the pursuit of innovative molecular catalysts for the electrocatalytic reduction of CO2, we employed computational methodologies to investigate six Cu‐based expanded porphyrin dual‐atom catalysts (DACs). Our study revealed both large and small variations among the different DACs. Despite metal center substitutions, the highly delocalized nature of the π orbitals in the expanded porphyrin complexes led to minimal differences between the frontier orbitals. Conversely, pronounced differences emerged during hydrogen reduction. Notably, the formation of H2 exhibited low limiting potentials ranging from 0.13 to 0.43 eV, attributable to the ligand‐centered activity of the expanded porphyrin. Similar limiting potentials (< 0.31 eV) for CO2 reduction indicate competition between the two reduction processes. This can be attributed to the emergence of highly favorable bridging μ2 intermediates, exemplified by *OCHO and *OH. The preference for these intermediates is expected to lead to the formation of only 2e‐ and 4e‐ products, namely H2, HCOOH and H2CO. Specifically, CuFe and CuMn DACs are poised to favor CO2 reduction to produce HCOOH and H2CO, while CuCo, CuCu, and CuZn DACs are anticipated to favor the production of H2.

Expanded Porphyrin Exhibiting Off-Centered Out-of-Plane Coordination to Dysprosium

Expanded Porphyrin Exhibiting Off-Centered Out-of-Plane Coordination to Dysprosium

Near-infrared absorption of fused core-modified expanded porphyrins for dye-sensitized solar cells.

Photophysical, photovoltaic, and charge transport properties of fused core-modified expanded porphyrins containing two pyrroles, one dithienothiophene (DTT) unit, and 1-4 thiophenes (1-4) were inspected by using density functional theory (DFT) and time-dependent DFT. Compounds 1-3 have been investigated experimentally before, but 4 is a theoretical proposal whose photophysical features match those extrapolated from 1 to 3. They exhibit absorption in the range of 700-970nm for their Q bands and 500-645nm for their Soret bands. The rise of thiophene rings placed in front of the DTT unit in the expanded porphyrin ring causes a bathochromic shift of the longest absorption wavelength, leading to near-infrared absorptions, which represent 49% of the solar energy. All the systems show a thermodynamically favorable process for the electron injection from the dye to TiO2 and adsorption on a finite TiO2 model. The electron regeneration of the dye is only thermodynamically feasible for the smallest expanded porphyrins 1 and 2 when I-/I3- electrolyte is used. The charge transport study shows that for voltages lower than 0.4V, junctions featuring pentaphyrin 1 and octaphyrin 4 are more conductive than those containing hexaphyrin 2 or heptaphyrin 3. The results showed that the four fused core-modified expanded porphyrins investigated are potential dyes for applications in dye-sensitized solar cells, mainly pentaphyrin 1 and hexaphyrin 2. Moreover, increasing the number of thiophene rings in the macrocycle proved fruitful in favoring absorption in the near-infrared region, which is highly desired for dye-sensitized solar cells.

A New Strategy for the Synthesis of Porphyrin and Expanded Porphyrin Derivatives from Di‐ and Tripyrromethanes: Antioxidant, Cytotoxic Activity, and Molecular Docking Evaluation

AbstractWe present a novel and effective process for producing porphyrins in the absence of a solvent condition, in contrast to earlier procedures. An aldehyde and pyrrole were condensed by grinding in the presence of an acidic catalyst during the synthetic process. By adjusting reactant molar ratios and concentrations, dipyrromethane 3 and tripyrromethane 4 derivatives, the synthesis was improved at room temperature in 5–10 minutes with excellent yields. In this work, we successfully synthesized a number of novel porphyrin derivatives, 6 b–j. Here, we describe a method for reacting dipyrromethane 3a with various aryl aldehydes 5 b–j while using DMF as a capping agent. Moreover, expanding porphyrin derivatives 7 a, and 7 b were synthesized from the reaction of 4a with aldehydes 5a and 5b at 0 °C. Porphyrin derivatives 6 g and 6 h displayed good antioxidant potential. The cytotoxic activity of compounds 6 h, 6 b, and 6c against the human cell lines HePG‐2 and MCF‐7 were studied. The binding modes of the synthesized compounds were analyzed by docking studies that showed good binding scores against the diverse amino acids of the selected proteins (Bcl‐2). The conducted docking studies were found to be consistent with cytotoxic results.

Cover Feature: Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins (Chem. Eur. J. 6/2023)

The aromaticity of charged expanded porphyrins turns out to be much more complex to study than that of their planar neutral analogues. In particular, identifying the most conjugated circuit is no longer straightforward. In addition to planarity, the protonation and deprotonation of porphyrinoids play an important role in determining their aromaticity. We have demonstrated that the largest charged porphyrins do not present a clear main conjugation pathway. Among the preferred aromatic indices, AVmin ends up being the most useful tool for recognizing the most aromatic path. We can relate the difficulty of finding the most conjugated path of a porphyrin to the number of pieces in a puzzle. Thus, the neutral state of the [36]octaphyrin is represented as a puzzle with few pieces; the protonated and deprotonated states are presented as puzzles with more pieces to indicate that they are more difficult to complete. More information can be found in the Research Article by M. Torrent-Sucarrat, E. Matito, M. Alonso, and co-workers (DOI: 10.1002/chem.202202264).

Near-Infrared Absorption of Fused Core-Modified Expanded Porphyrins for Dye-Sensitized Solar Cells

Near-Infrared Absorption of Fused Core-Modified Expanded Porphyrins for Dye-Sensitized Solar Cells

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins.

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins.

Theoretical analysis of expanded porphyrins: Aromaticity, stability, and optoelectronic properties

Expanded porphyrin systems are capable of binding a variety of substrates due to their increased cavity size and aromatic nature, holding important applications as magnetic resonance imaging contrast agents and as sensitizers for photodynamic therapy. It is there of fundamental interest to know the photoelectrical properties of expanded porphyrins using quantum chemistry calculations. In this work, we theoretically designed and screened a series of expanded porphyrins by incorporating terthiophene (TTH) and dithienothiophene (DTT) moieties. Our calculations showed that all the designed molecules exhibit excellent optoelectronic performance than the reference molecule. It is suggested that the porphyrin molecule with TTH moiety has better stability than the one with DTT moiety. Finally, we demonstrated that molecule 2 features with TTH moiety and the inverted selenophene ring outperform other molecules because it exhibits increased HOMO-LUMO gap, planar geometry, and strengthened aromaticity. We expect that this work can provide theoretical guidelines for the design of novel porphyrin materials.

1,4-Phenylene-Incorporated Decaphyrin(1.0.1.0.0.1.0.1.0.0): Synthesis, Structure, and Topological Chirality.

Expanded porphyrins represent emerging structures in realizing topological chirality; however, their inherent flexibility has hampered the effective chiral resolution. Herein, we rationally designed a decaphyrin 9, which could be separated into its enantiomers in the free-base form. The enantiomers showed noteworthy chiroptical properties, e.g., the intense circular dichroism response in the visible spectrum, and high absorption dissymmetry factors (gabs) of 0.036 at 618 nm. Theoretical analyses further explained the origin of the high gabs value.

Synthesis of Pyridine-Containing Crowned Fused Expanded Porphyrins.

New examples of nonaromatic fused expanded porphyrins containing both pyridine and crown ether moiety as a part of macrocyclic framework were synthesized by condensing pyridine based pentapyrrane with polyether-based diol in CH2 Cl2 in the presence of one equivalent of BF3 ⋅ OEt2 under inert conditions followed by oxidation with DDQ in open air. The condensation was expected to form pyridine-containing crowned expanded porphyrins but resulted in the formation of fused crowned expanded porphyrins due to intramolecular fusion of two pyrrole nitrogens with two adjacent inverted thiophene carbons as revealed by X-ray crystallography obtained for one of the macrocycle. HRMS and NMR studies supported the formation of fused crowned pyridine containing expanded porphyrins, and the macrocycles showed simple, well-resolved NMR spectra where all resonances were identified easily by 2D NMR spectroscopy. The macrocycles exhibited typical nonaromatic absorption features and showed one broad band with peak maxima at 535 nm and one or two shoulder bands in the higher energy region. The protonation studies resulted in clear colour change from purple to blue and absorption bands experienced bathochromic shifts with a broad band at 662 nm which was extended up to 800 nm. The electrochemical studies revealed that the macrocycles were easier to oxidize but difficult to reduce. DFT studies indicated that the macrocycle attains a very puckered and distorted 'U' shaped structure owing to the flexibility of the crown ether chain and TD-DFT studies corroborated experimental results. The preliminary studies indicated that the macrocycles could be used as colorimetric optical sensor for the detection of Cu2+ ion.

Theoretical Analysis of Expanded Porphyrins: Aromaticity, Stability, and Optoelectronic Properties

Theoretical Analysis of Expanded Porphyrins: Aromaticity, Stability, and Optoelectronic Properties

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

Role of O Substitution in Expanded Porphyrins on Uranyl Complexation: Orbital- and Density-Based Analyses

Search for new U(VI) sequestering macrocyclic ligands is an important area of research due to manifold applications. Besides hard- or soft-donor-based ligands, mixed-donor ligands are also gaining popularity in achieving optimized performances. However, how the combination of hard-soft-donor centers alters the bonding interactions with U(VI) is still not well-understood. Moreover, a consensus is yet to be reached on the nature and role of underlying covalent interactions in mixed N,O-donor ligands. In this work, using the relativistic density functional theory (DFT), we attempted to address these intriguing issues by investigating the subtle change in bonding characteristics of the uranyl ion upon binding with an expanded porphyrin, viz. sapphyrin, with subsequent O substitutions at the cavity. The results obtained from a range of modern analysis tools suggest that in the O-substituted sapphyrin variants, UO22+ prefers to bind with N over O, and an increase in the number of O-donor sites at the cavity prompts UO22+ to have a better interaction with the rest of the N-donor-centers. Although O donors are involved in more numbers of mixed molecular orbitals, the variation in the amplitude of overlap and the better σ-donation ability favor N to have stronger bonding interactions with uranyl. Molecular orbital (MO) and density of states (DOS) analyses show favorable participation of U(d), and the involvement of U(f) orbitals in bonding is of a low extent but non-negligible. Although electrostatic interaction dominates at U-O/N bonds in the equatorial plane, the quantum theory of atoms in molecules descriptors, MO analysis, and overlap-integral calculations confirm the presence of underlying near-degeneracy-driven covalent interactions.

Near-Infrared Optical Properties and Charge Transport in Expanded Porphyrins

Expanded porphyrins have been widely studied due to their potential application to optoelectronic devices and sensors. Several modifications in their molecular structures can be made in this type of molecules that lead to the modulation of their properties related to the electronic structure.In the search to improve the properties of these systems to be used in solar cells or electronic devices, we have investigated various strategies at the molecular and electronic structure, performing quantum mechanical simulations of the optical, magnetic, and charge transport properties.We investigated the effect of pyrrolic ring expansion in porphyrins fused with sulfur atoms; pentaphyrin, hexaphyrin, heptaphyrin, and octaphyrin (Figure 1), on the photophysical properties. The electronic absorption spectra were calculated with the time-dependent density functional theory (TD-DFT) approach in the solution phase. The expansion of pyrrolic rings produces an important bathochromic shift of the Q bands, where the absorption of the longest wavelength appears in the range of 745-970 nm. The effect of the extension of the π conjugation and the degree of distortion of the planarity of the macrocycle were also studied.Another strategy used was the formation of dyads composed of dyes, where one of them is a porphyrin or expanded porphyrin (smaragdyrin). We investigated the effect of substituents in the ß position of the porphyrin bound to a squaraine [1], as well as the effect of the bridging structure that connects smaragdyrin with a BODIPY derivative [2] (Figure 2). TD-DFT calculations for the dyads indicate that those with amines as substituents show a red-shift of the Q bands. Charge transfer bands calculated with TD-DFT and the perturbative approximation ΔSCF show a push effect on porphyrin and a pull effect on squaraine. Current-voltage calculations obtained for a molecular junction of the dyad connected to Au (111) nanowires to simulate the electrodes indicate that the charge transfer follows the same trend, in the sense from porphyrin to squaraine and is more favorable with the amine groups.Bimetallic hexaphyrins (Zn(II), Cu(II)) of the amethyrin type were also investigated, and it was found that the singlet Cu(II) systems show a significant shift towards the near-infrared (900 nm). Conductance and current-voltage profiles were calculated for molecular junctions with Au (111) electrodes. It was found that the effect of the anchoring group on the electrode is more relevant than the metal effect on the conductance. The important difference in the current of the triplet and singlet configuration of Cu(II) for a voltage range of 0.1-0.5 V suggests that this system could be used as a molecular switch.In summary, different strategies will be shown to modulate the optical properties for obtaining photosensitizers that can be used in dye-sensitized solar cells. Furthermore, the properties of charge transport are evaluated in the ground state to evaluate the ability of the molecular systems to transfer electrons to the electrodes.

Assessment of New Expanded Porpholactones as UV/Vis/NIR Chromophores for Dye-Sensitized Solar Cell Applications

Expanded porphyrins arise as an alternative for potential application as chromophores in dye-sensitized solar cells. (DSSCs). The modification of the core of these compounds provides remarkable changes in the photoelectronic behavior. In the present article, the improvement of its properties for a potential application as UV/vis/NIR chromophores in DSSCs has been studied, when an oxazolone moiety has replaced an imine ring in analogy to the porpholactones first synthesized by Crossley et al. ( J. Chem. Soc., Chem. Commun. 1984, 920-922). These expanded porpholactones present a noticeable red shift as well as an increase in the intensity of the Q-bands regarding the parent compounds. The photophysical properties of Sapphyrin have been explored through DFT calculations and vibrationally resolved absorption spectra simulations. Energetic parameters showed favorable electron injection from the chromophore to the TiO2 semiconductor. In addition, aromaticity was analyzed and rationalized using magnetic and delocalization criteria. Results showed qualitatively similar trends between aromaticity descriptors and Q bands giving a great opportunity to the use this property in the rational design of chromophores. Finally, the nonequilibrium Green's function formalism shows the ability of expanded porpholactones in electron transport.

Mechanochemically Triggered Topology Changes in Expanded Porphyrins.

A hitherto unexplored class of molecules for molecular force probe applications are expanded porphyrins. This work proves that mechanical force is an effective stimulus to trigger the interconversion between Hückel and Möbius topologies in [28]hexaphyrin, making these expanded porphyrins suitable to act as conformational mechanophores operating at mild (sub‐1 nn) force conditions. A straightforward approach based on distance matrices is proposed for the selection of pulling scenarios that promote either the planar Hückel topology or the three lowest lying Möbius topologies. This approach is supported by quantum mechanochemical calculations. Force distribution analyses reveal that [28]hexaphyrin selectively allocates the external mechanical energy to molecular regions that trigger Hückel–Möbius interconversions, explaining why certain pulling scenarios favor the Hückel two‐sided topology and others favor Möbius single‐sided topologies. The meso‐substitution pattern on [28]hexaphyrin determines whether the energy difference between the different topologies can be overcome by mechanical activation.

Expanded porphyrins: functional photoacoustic imaging agents that operate in the NIR-II region.

Photoacoustic imaging (PAI) relies on the use of contrast agents with high molar absorptivity in the NIR-I/NIR-II region. Expanded porphyrins, synthetic analogues of natural tetrapyrrolic pigments (e.g. heme and chlorophyll), constitute as potentially attractive platforms due to their NIR-II absorptivity and their ability to respond to stimuli. Here, we evaluate two expanded porphyrins, naphthorosarin (1) and octaphyrin (4), as stimuli responsive PA contrast agents for functional PAI. Both undergo proton-coupled electron transfer to produce species that absorb well in the NIR-II region. Octaphyrin (4) was successfully encapsulated into 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG2000) nanoparticles to afford OctaNPs. In combination with PAI, OctaNPs allowed changes in the acidic environment of the stomach to be visualized and cancerous versus healthy tissues to be discriminated.

Benzene- and pyridine-incorporated octaphyrins with different coordination modes toward two PdII centers

Expanded porphyrins have received considerable attention due to their unique optical, electrochemical and coordination properties. Here, we report benzene- and pyridine-incorporated octaphyrins(1.1.0.0.1.1.0.0), which are synthesized through Suzuki-Miyaura coupling of α,α′-diboryltripyrrane with m-dibromobenzene and 2,6-dibromopyridine, respectively, and subsequent oxidation with 2,3-dicyano-5,6-dichlorobenzoquinone. Both octaphyrins are nonaromatic and take on dumbbell structures. Upon treatment with Pd(OOCCH3)2, the benzene-incorporated one gives a Ci symmetric NNNC coordinated bis-PdII complex but the pyridine incorporated one gives Ci and Cs symmetric NNNC coordinated bis-PdII complexes along with an NNNN coordinated bis-PdII complex bearing a transannular C–C bond between the pyrrole α-positions. In addition, these two pyridine-containing NNNC PdII complexes undergo trifluoroacetic acid-induced clean interconversion.

Performance of Localized Coupled Cluster Methods in a Moderately Strong Correlation Regime: Hückel-Möbius Interconversions in Expanded Porphyrins.

Localized orbital coupled cluster theory has recently emerged as a nonempirical alternative to DFT for large systems. Intuitively, one might expect such methods to perform less well for highly delocalized systems. In the present work, we apply both canonical CCSD(T) approximations and a variety of localized approximations to a set of flexible expanded porphyrins—macrocycles that can switch between Hückel, figure-eight, and Möbius topologies under external stimuli. Both minima and isomerization transition states are considered. We find that Möbius(-like) structures have much stronger static correlation character than the remaining structures, and that this causes significant errors in DLPNO-CCSD(T) and even DLPNO-CCSD(T1) approaches, unless TightPNO cutoffs are employed. If sub-kcal mol–1 accuracy with respect to canonical relative energies is required even for Möbius-type systems (or other systems plagued by strong static correlation), then Nagy and Kallay’s LNO-CCSD(T) method with “tight” settings is the suitable localized approach. We propose the present POLYPYR21 data set as a benchmark for localized orbital methods or, more broadly, for the ability of lower-level methods to handle energetics with strongly varying degrees of static correlation.