Photo-redox reactions of indole and ferric iron in water

New Insights into Photo-Fenton Chemistry: The Overlooked Role of Excited IronIII Species

“…48 As time delays, 2 I 13/2,11/2 population intersystem crossing to 4 G 5/2 population. Actually, the electronic configuration of 4 MCCE ( 4 T 1g ) is identical to that of Fe IV , except for the extra excited electron in the t 2g orbital in 4 Fe 3+ (Figures 4f and S28). Similarly, 2 MCCE ( 2 T 2g ) generated by further excitation of 4 MCCE ( 4 T 1g ) at 460 nm leaves the photoexcited hole in the e g orbital.…”

“…In an attempt to investigate the metal-centered transition characteristics and their attribution, the branched spectral term resolution of the Fe(H 2 O) 6 3+ 3d 5 -electron configuration was performed based on the Tanabe−Sugano diagram (Figure S26) while taking into account the orbital and spin interactions of electrons and the coupling of orbital and spin interactions, respectively. 36 As shown in Figure 3b, the Fe(H 2 O) 6 3+ 3d 5 -electron configuration can split into energy levels including 6 S, 4 G, 4 F, 2 I, 4 D, and other higher energy levels. Considering the spin−orbit coupling effect, these energy levels can further split into 2J + 1 energy levels.…”

“…The consequent delocalization hole in MC intravalence is where *Fe III oxidation capacity enhancement originates. The molecule is immediately excited in its 4 MCCE n−1 state after light absorption, followed by sequential Q n → D n → D 1 → Q 1 kinetics population of the Fe III initial excited quartet state. Covalency formed between σ* 2px antibond electron of H 2 O 2 and Fe 3d electron is the compensate mechanism for the 3d(e g ) charge depletion in the excited Fenton photosensitizer, which reduces the reaction energy barrier in the *Fe III participate path.…”

“… However, the issue of sluggish dynamics of Fe II generation still limits the practical applications of Fenton technique (eqs and , Text S1 and Figure S1). − F e ( I I ) + H 2 O 2 → F e ( I I I ) + • O H + normalO normalH − goodbreak0em3em⁣ k = 80 .25em normalM − 1 .25em s − 1 F e ( I I I ) + H 2 O 2 → F e ( I I ) + normalH normalO 2 • + H + goodbreak0em1em⁣ k = 9.1 × 10 − 7 .25em normalM − 1 .25em s − 1…”

“…Multiwavelength global analysis was conducted to investigate the *Fe III evolution kinetics. It was supposed that because the first ES is a dark state, 26 the molecule directly excited its 4 Characterization. The light-induced ES Fe III species were characterized by using femtosecond transient absorption spectroscopy (fs-TAS) with UV−vis detection (Text S8).…”