Visible light photocatalysis enables a broad range of organic transformations that proceed via single electron or energy transfer. Metal polypyridyl complexes are among the most commonly employed visible light photocatalysts. The photophysical properties of these complexes have been extensively studied and can be tuned by modifying the substituents on the pyridine ligands. On the other hand, ligand modifications that enable substrate binding to control reaction selectivity remain rare. Given the exquisite control that enzymes exert over electron and energy transfer processes in nature, we envisioned that artificial metalloenzymes (ArMs) created by incorporating Ru( ii ) polypyridyl complexes into a suitable protein scaffold could provide a means to control photocatalyst properties. This study describes approaches to create covalent and non-covalent ArMs from a variety of Ru( ii ) polypyridyl cofactors and a prolyl oligopeptidase scaffold. A panel of ArMs with enhanced photophysical properties were engineered, and the nature of the scaffold/cofactor interactions in these systems was investigated. These ArMs provided higher yields and rates than Ru(Bpy) 3 2+ for the reductive cyclization of dienones and the [2 + 2] photocycloaddition between C -cinnamoyl imidazole and 4-methoxystyrene, suggesting that protein scaffolds could provide a means to improve the efficiency of visible light photocatalysts.
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Platinum( ii ) binuclear complexes: molecular structures, photophysical properties, and applications
Platinum( ii ) binuclear complexes containing two platinum centers bridged by different types of ligands have received great research attention for their unique properties and potential applications in a variety of areas. The properties of these binuclear Pt( ii ) complexes, which could be significantly different from those of their mononuclear counterparts, are highly tunable by modifying their cyclometallating ligands and bridging ligands, as well as their structural configurations. The photophysical properties of these complexes involving a wide range of spectroscopic phenomena make them a very interesting class of materials to be spectroscopically studied. Applications of platinum( ii ) binuclear complexes have been explored in several areas, ranging from light emitting diodes, to sensors and photocatalysis. In this review, the molecular structures, photophysical properties, and applications of a variety of platinum( ii ) binuclear complexes are discussed. We intend to shed some light on the recent progress in this field and give a future outlook.
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- Award ID(s):
- 1664661
- NSF-PAR ID:
- 10099125
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 7
- Issue:
- 20
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 5910 to 5924
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Two‐coordinate carbene Cu(Ι) amide complexes with sterically bulky groups such as the diisopropyl phenyl (dipp) on the carbenes have been shown to have comparable performance to the phosphorescent emitters bearing heavy atoms such as iridium and platinum. These bulky groups enforce a coplanar molecular structure and suppress the nonradiative decay rates. Here, three different two‐coordinate Cu(Ι) complexes were investigated that bear a common thiazole carbene, 3‐(2,6‐diisopropylphenyl)‐4,5‐dimethylthiazol‐2‐ylidene, with only a single dipp group, and carbazolyl ligands with substituents of varying steric bulk
ortho to N. These substituents have a negligible impact on luminescence energies of the complexes but serve to modulate the rotation barriers along the metal–ligand coordinate bond. The geometric arrangement of ligands (syn ‐ oranti ‐conformer) in complexes with alkyl substituents were found to differ, beingsyn in the solid state versusanti in solution as revealed by crystallographic analysis and nuclear magnetic resonance spectroscopy. In addition, calculations were performed to determine potential energy surfaces for different conformations of the three complexes to provide a theoretical evaluation of rotation barriers around the metal–ligand bond axis. The relationship between rotation barriers and photophysical properties demonstrate that rates for nonradiative decay decrease with increasing bulk of the substituents on the carbazolyl ligand. -
Luminescent complexes of heavy metals such as iridium, platinum, and ruthenium play an important role in photocatalysis and energy conversion applications as well as organic light-emitting diodes (OLEDs). Achieving comparable performance from more–earth-abundant copper requires overcoming the weak spin-orbit coupling of the light metal as well as limiting the high reorganization energies typical in copper(I) [Cu(I)] complexes. Here we report that two-coordinate Cu(I) complexes with redox active ligands in coplanar conformation manifest suppressed nonradiative decay, reduced structural reorganization, and sufficient orbital overlap for efficient charge transfer. We achieve photoluminescence efficiencies >99% and microsecond lifetimes, which lead to an efficient blue-emitting OLED. Photophysical analysis and simulations reveal a temperature-dependent interplay between emissive singlet and triplet charge-transfer states and amide-localized triplet states.more » « less
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The synthesis, photophysics, and electrochemiluminescence (ECL) of four water-soluble dinuclear Ir( iii ) and Ru( ii ) complexes (1–4) terminally-capped by 4′-phenyl-2,2′:6′,2′′-terpyridine (tpy) or 1,3-di(pyrid-2-yl)-4,6-dimethylbenzene (N^C^N) ligands and linked by a 2,7-bis(2,2′:6′,2′′-terpyridyl)fluorene with oligoether chains on C9 are reported. The impact of the tpy or N^C^N ligands and metal centers on the photophysical properties of 1–4 was assessed by spectroscopic methods including UV-vis absorption, emission, and transient absorption, and by time-dependent density functional theory (TDDFT) calculations. These complexes exhibited distinct singlet and triplet excited-state properties upon variation of the terminal-capping terdentate ligands and the metal centers. The ECL properties of complexes 1–3 with better water solubility were investigated in neutral phosphate buffer solutions (PBS) by adding tripropylamine (TPA) as a co-reactant, and the observed ECL intensity followed the descending order of 3 > 1 > 2. Complex 3 bearing the [Ru(tpy) 2 ] 2+ units displayed more pronounced ECL signals, giving its analogues great potential for further ECL study.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9tc01585j
