Excited State Interaction of Ruthenium (II) Imidazole Phenanthroline Complex [Ru(bpy)2ipH]2+ with 1, 4‐Benzoquinone: Simple Electron Transfer or Proton‐Coupled Electron Transfer?. Issue 18 (27th June 2018)

• Record Type: Journal Article
• Authors: Khade, Rahul V.; Dutta Choudhury, Sharmistha; Pal, Haridas; Kumbhar, Avinash S.
• Is Part Of: Chemphyschem. Volume 19:Issue 18(2018)
• Page Start: 2380
• Page End: 2388
• Publication Date: 2018-06-27
• Subjects: proton coupled electron transfer -- electrochemistry -- excited states -- ruthenium -- transient absorption; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201800313
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The unidirectional proton coupled electron transfer (PCET) from the excited state of Ru(II) imidazole phenanthroline complex [Ru(bpy)2 ipH] 2+ to 1, 4‐benzoquinone, was studied by steady‐state (SS) and time‐resolved (TR) fluorescence and transient absorption (TA) measurements. The p K a (9.7) and p K a * (8.6) values of the complex suggest that it behaves as a photoacid on excitation. The difference in the quenching rates obtained from SS and TR fluorescence studies indicate participation of both dynamic quenching and static quenching involving the hydrogen bonded ipH ligand of [Ru(bpy)2 ipH] 2+ with the 1, 4‐benzoquinone quencher, formed in the ground state. Within the hydrogen bonded complex, the ruthenium centre acts as the electron donor, while the ipH ligand acts as the proton donor to the hydrogen bonded 1, 4‐benzoquinone that acts simultaneously both as the electron and proton acceptor. It is proposed that the static quenching in the hydrogen bonded [Ru(bpy)2 ipH] 2+ ‐1, 4‐benzoquinone pairs occurs involving the PCET mechanism, while the dynamic quenching occurs through the simple ET mechanism, on diffusional encounter of the isolated 1, 4‐benzoquinone with the excited [Ru(bpy)2 ipH] 2+ complex. The occurrence of broad TA bands around 420–430 nm suggests formation of both 1, 4‐benzoquinone radical anion as well as the 1, 4‐benzosemiquinone radical by the interaction of excited [Ru(bpy)2 ipH] 2+ with 1, 4‐benzoquinone, thus supporting the ET process in the studied system. Abstract : Which way please? The excited state interaction of the complex [Ru(bpy)2 ipH] 2+ (ipH=imidazole phenanthroline) with the quencher 1, 4‐benzoquinone was investigated by using steady‐state and time‐resolved fluorescence quenching and transient absorption studies.