Photoinduced Electron Transfer between Ruthenium-bipyridyl Complex and Methylviologen in Suspensions of Smectite Clays

Abstract

We examined photoinduced electron transfer (PET) in multicomponent aqueous suspensions composed of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy) 3 2+ , photocatalyst), methylviologen (1,1′-dimethyl-4,4′-bipyridinium dication, MV 2+ , electron acceptor), and ethylenediamine tetraacetate (EDTA, sacrificial electron donor) together with particles of smectite-type clays although previous studies indicated inhibition of the electron transfer from Ru(bpy) 3 2+ to MV 2+ in the presence of clay particles. Clays with different lateral particle sizes were compared: hectorite (Hect) and saponite (Sapo) with small particle sizes (∼30 nm) and fluorohectorite (FH) and montmorillonite (Mont) with large particle sizes (>0.1 μm). Clay particles were flocculated and were settled in many cases after the addition of Ru(bpy) 3 2+ , MV 2+ , and EDTA species, and the Ru(bpy) 3 2+ and MV 2+ cations were almost all adsorbed on the clay particles. When Hect and Sapo were used, reduction of MV 2+ was observed on the aggregated clay particles upon visible light irradiation indicating the occurrence of PET from Ru(bpy) 3 2+ to MV 2+ . However, the reaction was not observed for the samples where the clay particles were not settled. When FH and Mont were used, PET was not observed irrespective of the flocculation of clay particles. These results demonstrated that PET from Ru(bpy) 3 2+ to MV 2+ in the presence of clay particles is possible when the clay particles with small sizes are appropriately aggregated to allow interparticle electron hopping.

Real Time Quantification of Ultrafast Photoinduced Bimolecular Electron Transfer Rate: Direct Probing of the Transient Intermediate

“…MV 2+ is a wellknown electron acceptor used in several ET reactions, e.g., electron ejection from gold nanoparticle, 62 modified Zn porphyrin, 63 tris(2,2-bipyridine)ruthenium(II), 64 etc. Upon accepting an electron, MV 2+ forms a radical cation (MV •+ ), and that could be detected directly by the transient absorption spectroscopy.…”

Micellar effect on the photophysics of heteroleptic ruthenium(II)–phenanthrolinedisulfonato complexes

“…These observations indicate emission from the Ru(II)–phen MLCT state in [Ru(phen) 3 ] 2+ , and from the lower lying Ru(II)–dpsphen MLCT state in complexes II–IV . Such behavior is typical of the emissive MLCT state of mixed‐ligand Ru(II) complexes, where the emission arises from the lowest‐lying emitting state . The introduction of dpsphen leads to a red shift in the absorption maximum relative to that of complex I .…”

“…The study of the photophysical properties of polypyridyl complexes of ruthenium(II), [Ru(NN) 3 ] 2+ , in homogeneous and heterogeneous media has gained enormous interest because of their intriguing properties such as their strong absorption in the solar region, emission from the 3 MLCT state, moderate excited state lifetime, ability to undergo electron and energy transfer processes and high photostability .…”

Photofunctional Layered Materials

“…The segregation structure was found to be different depending on the molecular structure of porphyrin and the island size is a key factor responsible for enhancing fluorescence quenching by electron transfer from viologen to porphyrin. The photoinduced electron transfer through interparticle electron hopping from [Ru (bpy) 3 ] 2+ -intercalated clays (Kunipia F, Sumecton SA, Laponite, and fluorohectorite) to the dimethylviologen counterparts in the presence of ethylenediamine tetraacetate (sacrificial electron donor) was shown by Nakato et al [211]. The photoreduction occurred depending on the lateral size of the clay Fig.…”