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Article

Synthesis of a Ru(II) Complex with a Naphthoquinone-Annelated Imidazole Ligand Exhibiting Proton-Responsive Redox and Luminescent Behavior

1
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki 305-8571, Japan
2
State Key Laboratory of Fine Chemicals, Dalian University of Technology, 2 Linggong Rd., Dalian 116024, China
*
Author to whom correspondence should be addressed.
Academic Editor: Martin T. Lemaire
Inorganics 2021, 9(4), 24; https://doi.org/10.3390/inorganics9040024
Received: 30 January 2021 / Revised: 25 March 2021 / Accepted: 31 March 2021 / Published: 3 April 2021
(This article belongs to the Special Issue Redox-Active Ligand Complexes)
A mononuclear ruthenium complex, [RuII(L)(bpy)2](PF6), with a naphthoquinone-annelated imidazole ligand HL (2-(pyridin-2-yl)-1H-naphtho[2,3-d]imidazole-4,9-dione) was synthesized and structurally characterized. Electrochemical study reveals that the Ru complex shows four reversible redox waves at +0.98 V, −1.13 V, −1.53 V, and −1.71 V versus SCE in acetonitrile, which are assigned to Ru(II)/Ru(III), L/L•2−, and two bpy/bpy•− redox couples, respectively. The redox potential of Ru(II)/Ru(III) was positively shifted upon the addition of trifluoromethanesulfonic acid due to protonation of the L moiety, leading to stabilization of the Ru 4d orbital. In UV-vis absorption measurements for the Ru complex in acetonitrile, a metal-to-ligand charge transfer (MLCT) band was observed at 476 nm, which was shifted to 450 nm by protonation, which might be due to a decrease in the electron delocalization and stabilization of the π orbitals in L. The blue shift of the MLCT band by protonation was associated with a shift of an emission band from 774 nm to 620 nm, which could be caused by the decreased electronic delocalization in the MLCT excited state. These electrochemical and spectroscopic changes were reversible for the protonation/deprotonation stimuli. View Full-Text
Keywords: Ru(II) complex; single-crystal X-ray crystallography; electrochemistry; luminescence Ru(II) complex; single-crystal X-ray crystallography; electrochemistry; luminescence
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MDPI and ACS Style

Shiga, T.; Tachibana, M.; Oshio, H.; Nihei, M. Synthesis of a Ru(II) Complex with a Naphthoquinone-Annelated Imidazole Ligand Exhibiting Proton-Responsive Redox and Luminescent Behavior. Inorganics 2021, 9, 24. https://doi.org/10.3390/inorganics9040024

AMA Style

Shiga T, Tachibana M, Oshio H, Nihei M. Synthesis of a Ru(II) Complex with a Naphthoquinone-Annelated Imidazole Ligand Exhibiting Proton-Responsive Redox and Luminescent Behavior. Inorganics. 2021; 9(4):24. https://doi.org/10.3390/inorganics9040024

Chicago/Turabian Style

Shiga, Takuya, Minami Tachibana, Hiroki Oshio, and Masayuki Nihei. 2021. "Synthesis of a Ru(II) Complex with a Naphthoquinone-Annelated Imidazole Ligand Exhibiting Proton-Responsive Redox and Luminescent Behavior" Inorganics 9, no. 4: 24. https://doi.org/10.3390/inorganics9040024

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