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Cu(i): Vs. Ru(II) photosensitizers: Elucidation of electron transfer processes within a series of structurally related complexes containing an extended π-system

Zhang Y, Traber P, Zedler L, Kupfer S, Gräfe S, Schulz M, Frey W, Karnahl M, Dietzek B (2018)

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Publication Type: Journal article

Publication year: 2018

Journal

Book Volume: 20

Pages Range: 24843-24857

Journal Issue: 38

DOI: 10.1039/c8cp04595j

Abstract

Heteroleptic Cu(i) complexes are a promising alternative towards traditional Ru(ii) photosensitizers. In particular, Cu(i) complexes of the type [Cu(P^P)(N^N)]⁺, where N^N represents a diimine and P^P a bulky diphosphine ligand, are already successfully applied for photocatalysis, organic light-emitting diodes or dye-sensitized solar cells. Therefore, this study aims for the systematic comparison of three novel heteroleptic Cu(i) compounds, composed of xantphos (xant) as P^P ligand and different diimine ligands with an extended π-system in the backbone, with their structurally related Ru(ii) analogues. In these Ru(ii) photosensitizers [Ru(bpy)2(N^N)]²⁺ (bpy = 2,2′-bipyridine) the same N^N ligands were used, namely, dipyrido[3,2-f:2′,3′-h]quinoxaline (dpq) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz). To gain an in-depth understanding of the photoinduced charge transfer processes, the photophysical features of these complexes and their electrochemically oxidized/reduced species were studied by a combination of UV-vis absorption, resonance Raman and spectroelectrochemistry. (TD)DFT calculations were applied to qualitatively analyze these measurements. As a result, the heteroleptic Cu(i) complexes exhibit comparable charge transfer properties to their Ru(ii) analogues, i.e. upon visible light excitation they undergo a metal-to-ligand charge transfer to the diimine ligand(s). In contrast, the reduced Cu(i)- and Ru(ii)-dppz complexes show considerably different electronic transitions. The singly reduced Cu(i)-dppz complexes are able to accumulate an additional electron at the phenanthroline moiety upon blue-light excitation, which is beneficial for multi-electron-transfer reactions. Upon low-energy light irradiation electronic transitions from the dppz^- anion to the xant ligand are excited, which could shorten the lifetime of the photosensitizer intermediates in an unwanted way.

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How to cite

APA:

Zhang, Y., Traber, P., Zedler, L., Kupfer, S., Gräfe, S., Schulz, M.,... Dietzek, B. (2018). Cu(i): Vs. Ru(II) photosensitizers: Elucidation of electron transfer processes within a series of structurally related complexes containing an extended π-system. Physical Chemistry Chemical Physics, 20(38), 24843-24857. https://doi.org/10.1039/c8cp04595j

MLA:

Zhang, Ying, et al. "Cu(i): Vs. Ru(II) photosensitizers: Elucidation of electron transfer processes within a series of structurally related complexes containing an extended π-system." Physical Chemistry Chemical Physics 20.38 (2018): 24843-24857.

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