A discrete metallo-supramolecular assembly composed of six iron(II) cations and twelve redox-active terpyridine ligands has been developed for visible-light-driven photochemical reduction of CO2 to CO in aqueous solution. This system achieves a turnover number (TON) of 14,956 with 99.6% selectivity toward CO production when combined with an organic thermally activated delayed fluorescence (TADF) photosensitizer, 4CzIPN. The reaction proceeds rapidly with an initial turnover frequency (TOF) of 276 min⁻¹, demonstrating exceptional catalytic efficiency. The high performance is attributed to the ability of the terpyridine fragments within the assembly to be reduced by the excited state of the photosensitizer, which subsequently acts as an electron reservoir for CO2 reduction. The coordination-driven self-assembly process enables precise structural control and enhances electron transfer capability through extended conjugation and multiple redox-active sites.
The supramolecular architecture Fe6L6 was synthesized via the reaction of ligand Phdtpy—bearing two terpyridine moieties—with FeCl₂·4H₂O under mild conditions. Characterization by ¹H NMR, ¹³C NMR, 1H–1H COSY, and ESI-TOF-MS confirmed the formation of the target complex, with characteristic peaks corresponding to charge states from +4 to +9. UV–vis absorption spectroscopy revealed a strong MLCT band at 575 nm (ε = 1.16 × 10⁵ M⁻¹ cm⁻¹), indicative of charge transfer from Fe²⁺ to terpyridine ligands, along with higher-energy ligand-based π→π* transitions at 290 and 324 nm. Cyclic voltammetry showed three quasi-reversible reduction waves at −1.19, −1.32, and −1.98 V vs. SCE, assigned to sequential reductions of the terpyridine ligands. Notably, these potentials are significantly more accessible than those of the free ligand, indicating that coordination to Fe²⁺ stabilizes the reduced forms and facilitates electron uptake.
In photocatalytic tests, the Fe6L6/4CzIPN system was evaluated under visible light irradiation (420–650 nm, white LEDs) in DMF/H₂O mixtures. Remarkably, even in solutions containing up to 40% water, the system maintained high selectivity (99.6%) and produced CO efficiently, with TON increasing dramatically from 294 (in pure DMF) to 14,956 (in aqueous DMF). In contrast, a monomeric [Fe(tpy)₂]²⁺ complex yielded only a TON of 615 regardless of solvent composition. Control experiments confirmed that both Fe6L6 and 4CzIPN are essential for high activity; replacing 4CzIPN with Ru(bpy)₃²⁺ led to a drastic drop in TON (to 45). Isotopic labeling using ¹³CO₂ verified that CO originates from CO2 reduction, not side reactions.
Kinetic analysis revealed a linear increase in CO production over the first 24 minutes, yielding an initial TOF of 276 min⁻¹—the highest reported for iron-based systems. The apparent quantum yield (AQY) was measured at 2.8% at 440 nm (180 mW cm⁻²), confirming effective photon utilization. Despite its rapid onset, the system exhibited limited durability due to decomposition of both 4CzIPN and the ligand upon prolonged irradiation. However, post-irradiation addition of fresh Phdtpy and 4CzIPN enabled regeneration of catalytic activity, achieving up to 10,750 TON in cyclic runs. This suggests that while the organic components degrade, Fe²⁺ ions remain intact and can reassemble in situ, enabling recyclable operation.GAPDH Antibody MedChemExpress
In situ UV–vis–NIR studies provided mechanistic insight: upon illumination, the MLCT band at 575 nm disappeared, while new absorptions emerged at 734 and 913 nm—characteristic of radical anions formed on terpyridine ligands.PTPRD Antibody manufacturer These signals persisted longer in aqueous DMF than in dry DMF, indicating enhanced stability of reduced ligands in water-rich environments.PMID:34303573 Under CO2 atmosphere, these bands vanished rapidly as electrons were consumed for CO2 reduction, correlating with substantial CO evolution detected by GC. This confirms that the terpyridine fragments serve as transient electron reservoirs, transferring stored electrons to CO2 in a controlled manner.
This work demonstrates that discrete metallo-supramolecular assemblies based on redox-active ligands can outperform conventional mononuclear catalysts in photochemical CO2 reduction. By leveraging coordination-driven self-assembly, such systems achieve high efficiency, selectivity, and potential for recyclability—all critical features for practical solar fuel conversion technologies. Future efforts will focus on enhancing stability through robust ligand design and exploring analogous architectures for broader applications in sustainable energy chemistry.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com