Influence of the Linker Chemistry on the Photoinduced Charge‐Transfer Dynamics of Hetero‐dinuclear Photocatalysts

Abstract

To optimize light-driven catalytic processes, lightmediated multi-electron transfer dynamics in molecular dyads need to be studied and correlated with structural changes focusing on the catalytically active metastable intermediates.Here, spectro-electrochemistry has been employed to investigate the structure-dependent photoelectron transfer kinetics in catalytically active intermediates of two RuÀ Rh catalysts for light-driven NAD + reduction. The excited-state reactivity of short-lived intermediates was studied along different photo-reaction pathways by resonance Raman and time-resolved transient absorption spectro-electrochemistry with sub-picosecond time resolution under operando conditions. The results demonstrate, for the first time, how the bridging ligand serves as a (multi-)electron storage structure, mediates the strength of the electronic coupling of catalytic and photocenter and impacts the targeted electron transfer as well as parasitic electron-transfer kinetics.

New Twist on the Light-Switch Effect: Controlling the Fate of Excited States with pH in a 4-Hydroxy-thiazol-extended Ruthenium(II) Dppz Complex

“…Since the rapid MLCT-to-ILCT energy transfer recovers the Ru­(II) center and populates a dppz-centered ILCT state, it can be presumed that the comparably strong ESA between 400 and 500 nm stems from MLCT transitions ( e.g. , MLCT bpy and MLCT phen ), similar to TA data collected for singly reduced Ru­(II)-trisbipyridyl-type complexes. − On the other hand, the features at 345 and 620 nm are associated with ππ* ESA of a phz-centered state. ,, The decay of the signals of RuTzO – is characterized by a blue shift of the signals and the formation of an ESA band with a maximum at 473 nm and a defined shoulder at 490 nm.…”

Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes

“…The experimentally accessible TOF and BNAH yields naturally represent measures of the overall reaction performance resulting from several different elementary steps, , among which the initial excited-state electron transfer process is not necessarily the decisive factor. The recovery of the initial state of the photosensitizer after one-electron oxidation likely becomes a key step for the iridium­(III) complexes considered here.…”

“…In biological systems, the regioselective regeneration of the 1,4-NADH isomer from NAD + is orchestrated enzymatically, whereas in artificial settings this is typically achieved with an organometallic rhodium co-catalyst derived from [Cp*Rh­(bpy)­Cl] + , where Cp* = C 5 Me 5 – and bpy = 2,2′-bipyridine. , The catalytically active [Cp*Rh­(bpy)­H] + species can be photochemically generated by the consecutive transfer of two electrons from a sensitizer (Figure ) along with a proton transfer from a suitable source. Such catalytic cycles necessitate robust photosensitizers that can act as very strong electron donors under physiological conditions. , To date, several different types of heterogeneous photocatalysts, − including graphene-based materials, , semiconductors, and Cd-based nanocrystals, have been used for this purpose. , Among homogeneous photocatalysts, derivatives of [Ru­(bpy) 3 ] 2+ , − Zn porphyrins, − or xanthene dyes have been popular. Aside from eosin Y, which can coordinate to the abovementioned rhodium co-catalyst, thus enabling efficient intramolecular electron transfer within the resulting photosensitizer-rhodium dyad, the turnover frequencies (TOF) for both heterogeneous and homogeneous conditions have remained somewhat modest in many cases, with TOF values typically below 20 h –1 at room temperature.…”

Stability of Catalytic Centres in Light‐Driven Hydrogen Evolution by Di‐ and Oligonuclear Photocatalysts

“…Besides influencing the photophysical properties of these systems, [63,64] these different connection techniques also significantly influence the stability of the BL against pH, temperature and irradiation as well as the stability of the CC during light‐driven catalysis.…”