Peripheral Substituents Research Articles

C-C Coupling in sterically demanding porphyrin environments.

Unlike their planar counterparts, classic synthetic protocols for C-C bond forming reactions on nonplanar porphyrins are underdeveloped. The development of C-C bond forming reactions on nonplanar porphyrins is critical in advancing this field of study for more complex porphyrin architectures, which could be used in supramolecular assemblies, catalysis, or sensing. In this work a library of arm-extended dodecasubstituted porphyrins was synthesized through the optimization of the classic Suzuki-Miyaura coupling of peripheral haloaryl substituents with a range of boronic acids. We report on palladium-catalyzed coupling attempts on the ortho-, meta-, and para-meso-phenyl position of sterically demanding dodecasubstituted saddle-shaped porphyrins. While para- and meta-substitutions could be achieved, ortho-functionalization in these systems remains elusive. Furthermore, borylation of a dodecasubstituted porphyrin's meso-phenyl position was explored and a subsequent C-C coupling showed the polarity of the reaction can be reversed resulting in higher yields. X-ray analysis of the target compounds revealed the formation of supramolecular assemblies, capable of accommodating substrates in their void.

The Roles of Molecular Concavities in the Hierarchical Self-Assembly of Giant Tetrahedra for CO2 Uptake.

Giant tetrahedral molecules have sparked significant interest in the past decade due to their unique and diverse supramolecular nanostructures. The longer and bulkier peripheral substituents create deep molecular concavities and thus contribute to the different self-assembly behaviors compared to the conventional small tetrahedral molecules. In this study, a molecular giant tetrahedra, TetraNDI, was synthesized to investigate the important roles of the molecular concavities in the self-assembly mechanism. Single-crystal structural characterizations indicate that the TetraNDI takes its trigonal concavities to form 1D supramolecular columns, and its tetragonal concavities to reach close inter-columnar packing. The difficulty in occupying the concavities leads to the path-dependent phase behaviors of the giant tetrahedra. It is also found that the remaining molecular concavities in the supramolecular scaffolds affect the CO2 affinity of TetraNDI. With an understanding of the packing principles of molecular giant tetrahedra, the structure-property relationships could be better evaluated in the future and might broaden the horizon of porous materials.

Direction Modulation of Intramolecular Electric Field Boosts Hole Transport in Phthalocyanines for Perovskite Solar Cells.

Tuning the strength of intramolecular electric field (IEF) in conjugated molecules has emerged as an effective approach to boost charge transfer. While direction manipulation of IEF would be a potential way that is still unclear. Here, we leverage the control of peripheral substituents of conjugated phthalocyanines to chemically tune the spatial orientation of IEF. By analyzing the spatial swing of side chains using the Kolmogorov-Arnold representation and least squares algorithm, a comprehensive mathematical-physical model has been established. This model enables rapid evaluation of the IEF and maximum hole transport performance induced by spatial swings. The champion phthalocyanine as dopant-free hole transport material in perovskite solar cell realizes a record performance of 23.41 %. Greatly device stability is also exhibited. This work affords a new way to enhance hole transport capabilities of conjugated molecules by optimizing their IEF vector for photovoltaic devices.

Direction Modulation of Intramolecular Electric Field Boosts Hole Transport in Phthalocyanines for Perovskite Solar Cells

AbstractTuning the strength of intramolecular electric field (IEF) in conjugated molecules has emerged as an effective approach to boost charge transfer. While direction manipulation of IEF would be a potential way that is still unclear. Here, we leverage the control of peripheral substituents of conjugated phthalocyanines to chemically tune the spatial orientation of IEF. By analyzing the spatial swing of side chains using the Kolmogorov‐Arnold representation and least squares algorithm, a comprehensive mathematical‐physical model has been established. This model enables rapid evaluation of the IEF and maximum hole transport performance induced by spatial swings. The champion phthalocyanine as dopant‐free hole transport material in perovskite solar cell realizes a record performance of 23.41 %. Greatly device stability is also exhibited. This work affords a new way to enhance hole transport capabilities of conjugated molecules by optimizing their IEF vector for photovoltaic devices.

Intermolecular Gold‐Catalyzed Nitrene Transfer Employing Aryl Azides: An Access to 7‐Functionalized 2‐Aminoindoles

AbstractWe report on intermolecular gold‐catalyzed nitrene transfer, utilizing o‐functionalized aryl azides as nitrene transfer reagents. This catalytic reaction provides a modular route to 7‐functionalized 2‐aminoindoles. Due to the optimized reaction conditions (toluene, 80–100 °C), a variety of functional substituents proved compatible (36 examples; yields up to 98%). The reaction can be performed using both homogeneous and heterogeneous catalytic variants with a low catalyst loading (1 mol %). The synthetic potential of the obtained products was illustrated by post‐modifications of the indole backbone and peripheral substituents. A plausible reaction mechanism includes the generation of intermediate α‐imino carbenes directly from the o‐functionalized aryl azides or other nitrene sources, such as anthranils or benzofuroxans, which form during the reaction in the cases of the specific aryls.

Influence of Peripheral Substituents on Fe(II) Spin State in Complexes with Tridentate Schiff‐Base Ligands

AbstractSix Fe(II) complexes with substituted 6‐((quinoline‐8‐ylimino)methyl)phenolates (R2qsal) were synthesized. X‐ray crystal structure determination for [Fe(R2qsal)2], where R=F (1), Cl (2), Br (3), I (4), CF3/H (5), or CN/H (6), revealed mononuclear complexes that crystallize either solvent‐free in case of 1, 5, and 6 or as CH2Cl2 solvates in the case of 2, 3, and 4. Complexes 1–4, which contain π‐donating substituents, exhibit only high‐spin (HS) state, as shown by crystal structure analysis and magnetic measurements. In contrast, complexes 5 and 6, which contain electron‐withdrawing substituents, exist in the low‐spin (LS) state at lower temperatures but exhibit crossover to the HS state above 300 K. Electronic structure calculations show a good correlation between the relative energies of the LS and HS states and the experimentally observed behavior.

Peripheral substituent effect on ‘turn-on’ fluorescence of BODIPY derivatives for sensing benzene moieties

In this work, a series of dipyrrometheneboron difluoride (BODIPY) derivatives, BT-F, BT-H, and BT-OMe, was prepared to study the peripheral substituent effect on 'turn-on' fluorescent for benzene moieties including benzene, toluene, and xylene (BTX). The photophysical- and electrochemical properties of the three compounds were systematically studied by steady-state UV–visible and PL spectroscopies, and cyclic voltammetry along with DFT calculations. Among various organic solvents, all compounds selectively showed strong 'turn-on' fluorescence in BTX solvents, proving that these compounds can be used as BTX probes. As the portion of BTX increases, the emission band shows a hypsochromic shift, indicating that the enhanced emission originated from exciplex formation in the excited state. Among them, BT-OMe, which has methoxy groups at peripheral positions, showed the highest sensing capability to BTX. The electron-donating nature of the methoxy group enhances the electron population on the BODIPY core and the triphenylamine groups, which results in strong interaction with BTX in the excited state.

The role of spacer heteroatomic fragment in spectroscopic and luminescent behaviour of phenyl-substituted phthalocyanine complexes

Peripheral phenyl-substituted metal phthalocyanines with thio and oxa substitution in the spacer bridge fragment were obtained in the work. Spectroscopic properties were studied for the obtained complexes, and the main patterns of behavior and characteristics change depending on the solvent and the nature of the spacer atom. It is shown that the replacement of an oxygen atom in the bridge fragment of a peripheral substituent with a sulfur atom leads to a change in the values of the fluorescence quantum yields. It was revealed that the presence of a spacer fragment is one of the key factors that strongly influence both the solubility of phthalocyanine complexes and their aggregation behavior in various solvents.

Enhancing Spin-Orbit Coupling in an Indolocarbazole Multiresonance Emitter by a Sulfur-Containing Peripheral Substituent for a Fast Reverse Intersystem Crossing.

A fast reverse intersystem crossing (RISC) remains an ongoing pursuit for multiresonance (MR) emitters but faces formidable challenges, particularly for indolocarbazole (ICz) derived ones. Here, heavy-atom effect is introduced first to construct ICz-MR emitter using a sulfur-containing substitute, simultaneously enhancing both spin-orbit and spin-vibronic coupling to afford a fast RISC with a rate of 1.2×105s-1, nearly one order of magnitude higher than previous maximum values. The emitter also exhibits an extremely narrow deep-blue emission peaking at 456nm with full-width at half-maxima of merely 12nm and a photoluminescence quantum yield of 92%. Benefiting from its efficient triplet upconversion capability, this emitter achieves not only a high maximum external quantum efficiency (EQE) of 31.1% in organic light-emitting diodes but also greatly alleviates efficiency roll-off, affording record-high EQEs of 29.9% at 1000cdm-2 and 18.7% at 5000cdm-2 among devices with ICz-MR emitters.

Chlorophyll Pigments and Their Synthetic Analogs.

Oxygenic phototrophs use chlorophylls (Chls) as photosynthetically active pigments. A variety of Chl molecules have been found in photosynthetic eukaryotes including green plants, algae, and cyanobacteria. Here we review their molecular structures with stereochemistry, occurrence in light-harvesting antennas and reaction centers, biosyntheses in the late stage, chemical stabilities, and visible absorption maxima in diethyl ether. The observed maxima are comparable to those of semisynthetic Chl analogs, methyl pyropheophorbides, in dichloromethane. The effects of their peripheral substituents and core π-conjugation on the maxima of the monomeric states are discussed. Notably, the oxidation along the molecular x-axis in Chl-a produces its accessory pigments, Chls-b/c, and introduction of an electron-withdrawing formyl group along the y-axis perpendicular to the x-axis affords far-red light absorbing Chls-d/f.

The nonlinear optical properties of meso-substituted porphyrins using spatial self-phase modulation

Herein, we studied the nonlinear optical properties of four meso-substituted porphyrins (H2MHTPP, H2THTPP, H2DETPP, and H2TETPP) by the spatial self-phase modulation (SSPM) method, using CW lasers with wavelengths of 532 nm and 780 nm. All samples exhibit strong nonlinear response due to the thermal optical nonlinear effect at 532 nm, which corresponds to the strong absorption band. In addition, four porphyrin samples were calculated that have nonlinear refractive index coefficients of the same order of magnitude (10−10 m2/W) at 532 nm. However, four porphyrins exhibited different optical nonlinear responses affected by the type and numbers of peripheral substituents at 780 nm. This work is of significance for reasonably adjusting the structure of compounds and improving their third-order nonlinear optical coefficients.

Charged Porphyrins That Form Electronically Functional Ion Pairs and Assemblies Via I π– I π Interactions

π-Electronic ions with appropriate geometries and peripheral substituents provide assemblies through the interactions between charged building subunits, resulting in fascinating electronic properties. Structures and properties of the assemblies can be controlled by the combined positively and negatively charged species in the assemblies.[1–3] In fact, π-electronic ion pairs comprising porphyrin-based π-electronic anions have exhibited characteristic assembling modes via i π– i π interactions and resulting electronic properties such as solid-state absorption, which was correlated with the arrangement of constituent charged π-systems, and photoinduced electron transfer.[4] Among various combinations of the porphyrin anions with porphyrin–AuIIIcomplexes as π-electronic cations,[5] the “activated” ion pair of meso-EWG (electron-withdrawing group)-substituted cation and meso-EDG (electron-donating group)-substituted anion exhibited the electron transfer in the ground state, resulting in the production of the heterodiradical in a close stacking structure as revealed by the ESR.[6] Further modifications of charged porphyrins and analogs have been examined for the electronic properties that are derived from ion pairing.[1] Recent reviews: (a) Haketa, Y.; Yamasumi, K. et al. Chem. Soc. Rev. 2023, 52, 7170; (b) Haketa, Y. et al. Responsive Mater. 2023, 1, e20230018. [2] Recent reports on ion pairs and assemblies: (a) Yamasumi, K. et al. Angew. Chem. Int. Ed. 2023, 62, e202216013; (b)Sugiura, S. et al. J. Am. Chem. Soc. 2023, 144, 8122; (c) Haketa, Y. et al. Chem. Sci. 2024, 15, in press (DOI: 10.1039/d3sc04564a). [3] Selected reports on pyrrole-based π-electronic molecules: (a) Haketa, Y. et al. J. Am. Chem. Soc. 2020, 142, 16420; (b) Ishikawa, S. et al. under revision. [4] Sasano, Y.; Tanaka, H. et al. Chem. Sci. 2021, 12, 9645. [5](a) Haketa, Y. et al. iScience 2019, 14, 241; (b) Nakajima, R. et al. to be submitted; (c) Maruyama, Y. et al. to be submitted. [6](a) Tanaka, H. et al. J. Am. Chem. Soc. 2022, 144, 21710; (b) Tanaka, H. et al. Chem. Eur. J. 2023, 29, e202203957.

Peri-Benzo-Diindenotetracenyl: Helically π-Extended Allyl Radical with Robust Stability.

Here is described the synthesis and characterization of a stable hydrocarbon radical, peri-benzo-diindenotetracenyl, with a helical structure. Although the helical π-radical has no peripheral substituents, it was stable in the solid and solutions. According to the X-ray diffraction analysis and quantum chemical calculations, the radical was best described as an allyl radical fused by five Clar's sextets. The optically resolved enantiomers exhibited mirror image CD spectra with |gCD| of 2.4×10-4 at 522 nm. The racemization barrier was determined to be 95.9 kJ/mol at 298 K, which is compatible with that of [5]helicene (108 kJ/mol).

3d-metal macrocyclic complexes containing porphyrazine/ perfluoroporphyrazine and fluoro ligands: Structural and thermodynamic parameters according to the various DFT model chemistries

By using three independent of density functional theory (DFT) model chemistries with functionals B3PW91, M06 and OPBE, and the TZVP basis set, combining the D3 version of Grimme’s dispersion with the original D3 damping function, the molecular structures of three types of 3[Formula: see text] element (M) macrocyclic coordination compounds — homoligand with porphyrazine (H2L1), heteroligand with porphyrazine and two axially oriented fluoro ligands and heteroligand with perfluoroporphyrazine (H2L2) and two axially oriented fluoro ligands having [ML1], [ML1(F)2] and [ML2(F)2] compositions, respectively, were calculated. The values of the most important bond lengths, bond and non-bond angles in the resulting metal complexes, and NBO analysis data are presented. It was noted that almost each of these complexes contains a coplanar MN4 chelate unit and a group of N4 atoms, as well as coplanar 5- and 6-membered rings; moreover, both of them are pairwise identical to each other in terms of the sums of bond angles (540[Formula: see text] and 720[Formula: see text], respectively) and their assortments. Bond angles formed by M atoms and two fluorine atoms are 180[Formula: see text]; bond angles formed by fluorine, M and nitrogen atoms are 90[Formula: see text]. NBO analysis of all the above 3[Formula: see text]-metal chelates was carried out, and based on the data, a high degree of delocalization of the electron density in these coordination compounds was stated. The values of the standard enthalpy [Formula: see text], entropy [Formula: see text] and Gibbs energy [Formula: see text] of formation of these compounds were also calculated. Particular attention was paid to the fact that according to these data, for the ([ML1]) and ([ML1(F)2]) complexes the values of [Formula: see text] and [Formula: see text] are positive, whereas for ([ML2(F)2]) complexes they are negative, and in the series [ML1] – [ML1(F)2] – [ML2(F)2] there is an increase in the thermodynamic stability of the complexes, which is undoubtedly due to the presence of peripheral fluorine substituents in the [ML2(F)2] structure. There was also good agreement between similar parameters calculated by different DFT methods, both qualitatively and quantitatively.

Enhanced photodetection in organic semiconductor single crystal sensitized by a tailored synergistic absorption of capsule-shaped chlorophyll derived CQDs

Organic single-crystal phototransistors have emerged as one of the most promising light signal detectors for their minimal defects, high mobility and light sensitivity. However, fully exploiting their advantages in advanced flexible optoelectronic applications remains great difficulty and challenging due to the lack of efficient methods for upgrading the photoresponse of delicate organic crystalline materials. Herein, we developed a capsule-shaped chlorophyll derived carbon quantum dots (Chl-CQDs) to enhance the single-crystal photodetection. Through a multi-site carbonization of chlorophyll peripheral substituents, the CQDs were produced around the chlorophyll tetrapyrrole macrocyclicvia. It makes Chl-CQDs combine the light absorption advantages of chlorophyll and CQDs, and exhibit an amazing synergistic absorption behavior. Compared to pristine devices of 2,6-diphenyl anthracene (DPA), the key figures of merit such as P, R, and D* of the Chl-CQDs/DPA heterophototransistors are improved by over 6000 times, 5 times, and 200 times, respectively. Additionally, an ultra fast charge transfer dynamics (τrise = 35 ms and τdecay = 45 ms) is observed at such unique type II heterointerface. These results not only offer a new approach for improving the photoresponse of single crystal organic phototransistors, but also make it possible to be superior to that of silicon-based devices.

Exploring the Role of Central Metals in Bulky Phthalocyanines for Dye-Sensitized Solar Cells.

Two series of metallo-(Zn(II), Mg(II), and Ru(II)) and free-base phthalocyanines (Pcs) with a carboxyl anchoring group and well-established bulky peripheral substituents (either tert-butyl or bulky 2,6-diisopropylphenoxy) were synthesized and tested as sensitizers in dye-sensitized solar cells (DSSCs). The trend of photovoltaic efficiencies (PCEs) for free-base and metallo Pcs followed the order Zn(II)Pc>Mg(II)Pc≫H2Pc ≈ Ru(II)Pc regardless of the peripheral substitution. Higher efficiencies (4.95 versus 3.63 for the Zn(II) derivatives) were achieved with Pcs bearing the bulkier 2,6-diisopropylphenoxy group, indicating a lower aggregation and more suitable HOMO-LUMO levels. Furthermore, these derivatives showed a morelevant influence of the metal on the PCE values (from the highest 4.95 for the Zn(II)Pc to the lowest 0.23 for the Ru(II)Pc. In both series, the best PCEs observed with the Zn(II) derivatives were mainly due to their highest Jsc values. The lowest efficiencies found for the free-bases and Ru(II) derivatives were attributed to a mismatch between their LUMO levels and the conduction band of the TiO2,and lower light-harvesting capabilities, respectively. In conclusion, Zn(II) derivatives are still the best Pc candidates to use as sensitizers in molecular photovoltaics.

Tailored Metal-Porphyrin Based Molecular Electrocatalysts for Enhanced Artificial Nitrogen Fixation to Green Ammonia.

Electrochemical nitrogen reduction (E-NRR) is one of the most promising approaches to generate green NH3. However, scarce ammonia yields and Faradaic efficiencies (FE) still limit their use on a large scale. Thus, efforts are focusing on different E-NRR catalyst structures and formulations. Among present strategies, molecular electrocatalysts such as metal-porphyrins emerge as an encouraging option due to their planar structures which favor the interaction involving the metal center, responsible for adsorption and activation of nitrogen. Nevertheless, the high hydrophobicity of porphyrins limits the aqueous electrolyte-catalyst interaction lowering yields. This work introduces a new class of metal-porphyrin based catalysts, bearing hydrophilic tris(ethyleneglycol) monomethyl ether chains (metal = Cu(II) and CoII)). Experimental results show that the presence of hydrophilic chains significantly increases ammonia yields and FE, supporting the relevance of fruitful catalyst-electrolyte interactions. This study also investigates the use of hydrophobic branched alkyl chains for comparison, resulting in similar performances with respect to the unsubstituted metal-porphyrin, taken as a reference, further confirming that the appropriate design of electrocatalysts carrying peripheral hydrophilic substituents is able to improve device performances in the generation of green ammonia.

Quantifying the effects of peripheral substituents on the spin-lattice relaxation of a vanadyl molecular quantum bit

Electron spin superpositions represent a critical component of emergent quantum technologies in computation, sensing, encryption, and communication. However, spin relaxation (T1) and decoherence (Tm) represent major obstacles to the implementation of molecular quantum bits (qubits). Synthetic strategies have made substantial progress in enhancing spin coherence times by minimizing contributions from surrounding electron and nuclear spins. For room-temperature operation, however, the lifetime of spin coherence becomes limited by coupling with vibrational modes of the lattice. Using pulse electron paramagnetic resonance (EPR) spectroscopy, we measure the spin-lattice relaxation of a vanadyl tetrapyrazinoporphyrazine complex appended with eight peripheral 2,6-diisopropylphenol groups (VOPyzPz-DIPP) and compare it to the relaxation of the archetypical vanadyl phthalocyanine molecular qubit (VOPc). The added peripheral groups lead to distinctly different spin relaxation behavior. While similar relaxation times are observed at low temperatures and ambient conditions, significant changes are observed for the orientation dependence of T1 at 100 K, as well as the temperature dependence of T1 over the intermediate temperature range spanning [Formula: see text]10–150 K. These results can be tentatively interpreted as arising from loosened spin-phonon coupling selection rules and a greater number of accessible acoustic and optical modes contributing to the spin relaxation behavior of VOPyzPz-DIPP relative to VOPc.

Memristors Based on Ni(II)‐tetraaza[14]annulene Complexes: Toward an Unconventional Resistive Switching Mechanism

AbstractIn this work, a family of Ni‐based dibenzotetraaza[14]annulene (dtaa) complexes are investigated for their application in memristors (memory resistors). A series of four Ni(II) complexes with different peripheral substituents of the dtaa ligand are successfully synthesized. Based on these compounds, two‐terminal thin‐film devices are fabricated in planar architecture. Four metals with different work functions are tested: Mg, Cu, Ni, and Au. It is demonstrated that ITO|[Ni(Me4dtaa)]|Cu devices show hysteretic behavior and offer stable, robust, and reproducible switching between high‐ and low‐resistive states. An in‐depth spectroscopic characterization of the Ni complex is performed, using radiation from infrared, through visible and ultraviolet, to tender X‐rays. Operando X‐ray fluorescence spectroscopy is used to monitor redox and structural changes upon the polarization of the studied memristor with the external electric field. Density functional theory calculations are used to better understand the electronic structure of the studied material, as well as structural rearrangement after electron injection that may be responsible for the modulation of electric conductivity. Finding a unique case of filamentary‐type resistive switching involving redox reactions of stationary molecules within a molecular solid is postulated. Yet, the formation of these filaments is not related to any significant configurational changes at the atomic scale.

Synthesis, X-ray Studies and Photophysical Properties of Iridium(III) Complexes Incorporating Functionalized 2,2':6',2″ Terpyridines and 2,6-Bis(thiazol-2-yl)pyridines.

A series of iridium(III) triimine complexes incorporating 2,2':6',2″-terpyridine (terpy) and 2,6-bis(thiazol-2-yl)pyridine (dtpy) derivatives were successfully designed and synthesized to investigate the impact of the peripheral rings (pyridine, thiazole) and substituents (thiophene, bithiophene, EDOT) attached to the triimine skeleton on their photophysical properties. The Ir(III) complexes were fully characterized using IR, 1H, elemental analysis and single crystal X-ray analysis. Their thermal properties were evaluated using TGA measurements. Photoluminescence spectra of [IrCl3L1-6] were investigated in solution at 298 and 77 K. The experimental studies were accompanied by DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were studied in detail by electronic absorption and emission. In solution, they exhibited photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure. The experimental research included DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were conducted using electronic absorption and emission techniques. In solution, they displayed photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure.