More Like this

1. The Zinc(II) Complexes of Four Constitutional Isomers of the Octaethyl‐ β , β ′‐dioxo‐bacterio‐ and ‐Isobacteriochlorin Series

   https://doi.org/10.1002/zaac.202500137  

   Chaudhri, Nivedita; Zeller, Matthias; Brückner, Christian (November 2025, Zeitschrift für anorganische und allgemeine Chemie)

   Treatment ofβ‐octaethylporphyrin with H₂O₂/conc. H₂SO₄to convert it to, inter alia, into all five constitutional isomers of the correspondingβ,β′‐dioxo‐derivatives—two bacteriochlorin‐type isomers and three isobacteriochlorin‐type isomers—is well‐known, as is the ability of some of the dioxo‐derivatives to form transition metal complexes. However, no comparative description of their zinc complexes has become known.This gap is closed here, and a description of the optical (UV–vis absorption and fluorescence emission) properties of their zinc(II) complexes is provided as the basis for their further study and utilization. The strongβ‐oxo auxochromes determine their optical properties that are distinctly different from archetype metallo‐bacteriochlorin or ‐isobacteriochlorin spectra. Herein, a description of the crystal X‐ray structures of three diketone isomer zinc complexes, including a detailed analysis of their macrocycle conformations, is presented. A new pictorial representation of the in‐ and out‐of‐plane distortions observed in the macrocycles of these complexes is taken advantage of to highlight their subtle but important differences. 

   more » « less
2. Co( ii ) complexes of tetraazamacrocycles appended with amide or hydroxypropyl groups as paraCEST agents

   https://doi.org/10.1039/d3dt01572f  

   Raymond, Jaclyn J.; Abozeid, Samira M.; Sokolow, Gregory E.; Bond, Christopher J.; Yap, Constance E.; Nazarenko, Alexander Y.; Morrow, Janet R. (July 2023, Dalton Transactions)

   Co( ii ) complexes of 1,4,7,10-tetraazacyclododecane (CYCLEN) or 1,4,8,11-tetraazacyclotetradecane (CYCLAM) with 2-hydroxypropyl or carbamoylmethyl (amide) pendants are studied with the goal of developing paramagnetic chemical exchange saturation transfer (paraCEST) agents. Single-crystal X-ray diffraction studies show that two of the coordination cations with hexadentate ligands, [Co(DHP)] 2+ and [Co(BABC)] 2+ , form six-coordinate complexes; whereas two CYCLEN-based complexes with potentially octadentate ligands, [Co(THP)] 2+ and [Co(HPAC)] 2+ , are seven-coordinate with only three of the four pendant groups bound to the metal center. 1 H NMR spectra of these complexes suggest that the six-coordinate complexes are present as a single isomer in aqueous solution. For the complexes which are seven-coordinate in the solid state, one is highly fluxional in aqueous solution on the NMR time scale ([Co(HPAC)] 2+ ), whereas the NMR spectrum of [Co(THP)] 2+ is consistent with an eight-coordinate complex with all pendants bound. Co( ii ) complexes of CYCLEN derivatives show CEST effects of low intensity that are assigned to NH or OH groups of the pendants. One complex, [Co(DHP)] 2+ , shows a highly-shifted CEST peak at 113 ppm versus bulk water, attributed to OH protons. However, the CEST effect is largest for two Co( ii ) CYCLAM-based complexes with coordinated amide groups that undergo NH proton exchange. All five complexes are inert towards dissociation in buffered solutions containing carbonate and phosphate and towards trans-metalation by excess Zn( ii ). These data give insight into the production of an intense CEST effect for tetraazamacrocyclic complexes with pendant groups containing NH or OH exchangeable protons. The intense and highly shifted CEST peak(s) of the CYCLAM-based complexes suggest that they are promising for further development as paraCEST agents. 

   more » « less
3. Photophysics and Electrochemistry of Biomimetic Pyranoflavyliums: What Can Bioinspiration from Red Wines Offer

   https://doi.org/10.3390/photochem2010003  

   Espinoza, Eli Misael; Clark, John Anthony; Billones, Mimi Karen; Silva, Gustavo Thalmer; Silva, Cassio Pacheco; Quina, Frank Herbert; Vullev, Valentine Ivanov (March 2022, Photochem)

   Natural dyes and pigments offer incomparable diversity of structures and functionalities, making them an excellent source of inspiration for the design and development of synthetic chromophores with a myriad of emerging properties. Formed during maturation of red wines, pyranoanthocyanins are electron-deficient cationic pyranoflavylium dyes with broad absorption in the visible spectral region and pronounced chemical and photostability. Herein, we survey the optical and electrochemical properties of synthetic pyranoflavylium dyes functionalized with different electron-donating and electron-withdrawing groups, which vary their reduction potentials over a range of about 400 mV. Despite their highly electron-deficient cores, the exploration of pyranoflavyliums as photosensitizers has been limited to the “classical” n-type dye-sensitized solar cells (DSSCs) where they act as electron donors. In light of their electrochemical and spectroscopic properties, however, these biomimetic synthetic dyes should prove to be immensely beneficial as chromophores in p-type DSSCs, where their ability to act as photooxidants, along with their pronounced photostability, can benefit key advances in solar-energy science and engineering. 

   more » « less
4. Electronic structure and photophysics of a supermolecular iron complex having a long MLCT-state lifetime and panchromatic absorption

   https://doi.org/10.1073/pnas.2009996117  

   Jiang, Ting; Bai, Yusong; Zhang, Peng; Han, Qiwei; Mitzi, David B.; Therien, Michael J. (August 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Exploiting earth-abundant iron-based metal complexes as high-performance photosensitizers demands long-lived electronically excited metal-to-ligand charge-transfer (MLCT) states, but these species suffer typically from femtosecond timescale charge-transfer (CT)-state quenching by low-lying nonreactive metal-centered (MC) states. Here, we engineer supermolecular Fe(II) chromophores based on the bis(tridentate-ligand)metal(II)-ethyne-(porphinato)zinc(II) conjugated framework, previously shown to give rise to highly delocalized low-lying 3 MLCT states for other Group VIII metal (Ru, Os) complexes. Electronic spectral, potentiometric, and ultrafast pump–probe transient dynamical data demonstrate that a combination of a strong σ-donating tridentate ligand and a (porphinato)zinc(II) moiety with low-lying π*-energy levels, sufficiently destabilize MC states and stabilize supermolecular MLCT states to realize Fe(II) complexes that express 3 MLCT state photophysics reminiscent of their heavy-metal analogs. The resulting Fe(II) chromophore archetype, FeNHCPZn, features a highly polarized CT state having a profoundly extended 3 MLCT lifetime (160 ps), 3 MLCT phosphorescence, and ambient environment stability. Density functional and domain-based local pair natural orbital coupled cluster [DLPNO-CCSD(T)] theory reveal triplet-state wavefunction spatial distributions consistent with electronic spectroscopic and excited-state dynamical data, further underscoring the dramatic Fe metal-to-extended ligand CT character of electronically excited FeNHCPZn. This design further prompts intense panchromatic absorptivity via redistributing high-energy absorptive oscillator strength throughout the visible spectral domain, while maintaining a substantial excited-state oxidation potential for wide-ranging photochemistry––highlighted by the ability of FeNHCPZn to photoinject charges into a SnO 2 /FTO electrode in a dye-sensitized solar cell (DSSC) architecture. Concepts enumerated herein afford opportunities for replacing traditional rare-metal–based emitters for solar-energy conversion and photoluminescence applications. 

   more » « less
5. Primary amines as ligands and linkers in complexes of tripyrrindione radicals

   https://doi.org/10.1142/S1088424623501109  

   Habenšus, Iva; Ghavam, Ameen; Curtis, Clayton J.; Astashkin, Andrei V.; Tomat, Elisa (July 2023, Journal of Porphyrins and Phthalocyanines)

   Biopyrrin pigments, which result from the degradation of heme in biological settings, feature three or two pyrrole rings and characteristic pyrrolin-2-one termini. These scaffolds serve as redox-active ligands and electron reservoirs in coordination compounds. Tripyrrin-1,14-dione coordinates divalent transition metals as a dianionic ligand hosting a delocalized radical. Herein, we report the synthesis and characterization of palladium(II) and platinum(II) tripyrrindione complexes featuring a primary amine (i.e., aniline, tert-butylamine, 1,2-ethylenediamine) at the fourth coordination site within square planar geometries. Interligand hydrogen-bonding interactions are observed between the coordinated amine and the carbonyl groups on the tripyrrindione scaffold. Notably, 1,2-ethylenediamine is employed to link two Pt(II) tripyrrindione complexes. As revealed by optical absorption and electron paramagnetic resonance (EPR) spectroscopy, all resulting complexes present ligand-based radicals that are stable at room temperature and when exposed to air. Spin pairing through multicenter interactions leads to [Formula: see text]-dimerization of the tripyrrindione radicals and a decrease in the EPR signal at low temperatures. Electrochemical measurements indicate that the ligand system undergoes quasi-reversible one-electron oxidation and reduction, thus confirming the ability of tripyrrindione to form square planar complexes in three different redox states. 

   more » « less