Pt(ii)-Catalyzed photosynthesis for H₂ evolution cycling between singly and triply reduced species

Abstract

A PtCl2(bpy) derivative tethered to two viologen (MV(2+)) moieties drives photochemical H2 evolution via forming a three-electron-reduced species possessing a bpy(-)˙-based (or MV(0)-based) reducing equivalent. Such species can only form after one electron reduction of both the MV(2+) sites because of rapid intramolecular electron transfer from bpy(-)˙ to MV(2+).

Tris(2,2′‐bipyridine)ruthenium Derivatives with Multiple Viologen Acceptors: Quadratic Dependence of Photocatalytic H2 Evolution Rate on the Local Concentration of the Acceptor Site

“…site (6.0 %) is considerably lower. As recently discussed for PtCl 2 (bpy) derivatives with multi‐viologen tethers, the reduction potential of the (MV + ) 2 π‐dimer site is 0.15 V positively shifted compared with that of the free MV + . site, and the approximately 0.12 eV loss in the driving force for H 2 evolution is caused by raising the pH from 5.0 to 7.0.…”

Photocatalytic H2 Evolution Using a Ru Chromophore Tethered to Six Viologen Acceptors

“…From the net time constant < τ >=10.3 ns (see the footnote in Table for detailed information), the net FET(1) rate ( k ET ) for [Ru(bpyMV2) 3 ] 14+ is estimated to be k ET =9.71×10 7 s −1 , which is slightly higher than that previously observed for [Ru(4,4′‐aspMV4) 3 ] 26+ ( k ET =6.50×10 7 s −1 ) (Table ) . However, it seems that shortening in the distance between the chromophore and the electron acceptors does not have an important effect on the FET(1) rate, although such a distance dependence of k ET was observed for related Pt II systems ,. Additional experiments were conducted by using nanosecond transient absorption spectroscopy (TAS) to analyze the rate of the back electron transfer from the MV +.…”

“…The bands located at λ =358, 527, and 868 nm are assigned as those derived from the diamagnetic (MV + ) 2 π dimer in which the two MV +. moieties stacked intramolecularly in a staggered fashion, as previously described for this bpyMV2 4+ ligand . The net number of electrons stored per PCS ( N ES ) and the relative abundances of the MV +.…”

“…The important finding here is not the N ES value but the relative abundance of non‐dimerized MV +. , which is known to serve as a stronger reducing equivalent towards water reduction when compared with the dimerized species . For instance, the molar ratio of MV +.…”

“…On the other hand, in our previous study which focused on [PtCl 2 (bpyMV2)] 4+ , the relatively short distance between the bpy and the viologen acceptors in the bpyMV2 4+ ligand led to enhance the electron‐transfer rate for both the forward and backward processes . These findings evidence that the water reduction efficiency driven by PCS systems can be improved by the rational design of the PCS framework.…”