Three Ru(bpy)32+derivatives tethered to multiple viologen acceptors, [Ru(bpy)2(4,4′-MV2)]6+, [Ru(bpy)2(4,4′-MV4)]10+, and [Ru(bpy)(4,4′-MV4)2]18+[bpy=2,2′-bipyridine, 4,4′-MV2=4-ethoxycarbonyl-4′-(N-G1-carbamoyl)-2,2′-bipyridine, and 4,4′-MV4=4,4′-bis(N-G1-carbamoyl)-2,2′-bipyridine, where G1=Asp(NHG2)-NHG2and G2=-(CH2)2-N+C5H4-C5H4N+-CH3] were prepared as “photo-charge separators (PCSs)”. Photoirradiation of these complexes in the presence of a sacrificial electron donor (EDTA) results in storage of electrons per PCS values of 1.3, 2.7, and 4.6, respectively. Their applications in the photochemical H2evolution from water in the presence of a colloidal Pt H2-evolving catalyst were investigated, and are discussed along with those reported for [Ru(bpy)2(5,5′-MV4)]10+, [Ru(4,4′-MV4)3]26+, and [Ru(5,5′-MV4)3]26+(Inorg. Chem. Front. 2016, 3, 671–680). The PCSs with high dimerization constants (Kd=105–106m−1) are superior in driving H2evolution at pH 5.0, whereas those with lower Kdvalues (103–104m−1) are superior at pH 7.0, where Kd=[(MV+)2]/[MV+.]2. The (MV+)2site can drive H2evolution only at pH 5.0 as a result of its 0.15 eV lower driving force for H2evolution relative to MV+., whereas the PCSs with lower Kdvalues exhibit higher performance at pH 7.0 owing to the higher population of free MV+.. Importantly, the rate of electron charging over the PCSs is linear to the apparent H2evolution rate, and shows an intriguing quadratic dependence on the number of MV2+units per PCS.
All Science Journal Classification (ASJC) codes
- Organic Chemistry