Supramolecular and Intramolecular Energy Transfer with Ruthenium–Anthracene Donor–Acceptor Couples: Salt Bridge versus Covalent Bond

Freys, Jonathan C.; Wenger, Oliver S.

doi:10.1002/ejic.201000815

Cited by 21 publications

(11 citation statements)

References 73 publications

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“…Earlier Beauchamp and co‐workers had shown that rhenium(III) complexes with biimidazole ligands not only bind halide anions via hydrogen bonds but also form hydrogen bond networks with benzoate anions . Energy transfer processes between metal complexes as well as organic triplet emitters and metal complexes have also been observed for hydrogen bonded systems which consisted of the biimidazole‐carboxylate motive . We were able to show that DNB quenches the phosphorescence of 12 by about 50 % in a 1:1 mixture in chloroform, and further addition of up to 8 equivalents leads to a residual luminescence of only about 8 % with respect to the pristine complex.…”

Section: Sensors For Small Anionssupporting

confidence: 52%

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

Rommel

Sorsche

Fleischmann

et al. 2017

Chemistry A European J

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Phosphorescent metal complexes with peripheral N-H donor functionalities have attracted great attention as potential molecular sensing units for anionic species lately. In this contribution we discuss the development and potential of anion recognition and sensing features of recent examples of luminescent 2,2'-biimidazole complexes of ruthenium(II), iridium(III), osmium(II) and cobalt(III). The general dependency of photophysical features in these complexes regarding the acid-base chemistry of the peripheral N-H functionalities will be outlined as a basic requirement for optical ion recognition. Systematic strategies for the tuning and specific improvement by synthetic means will be discussed regarding recent reports. With respect to their distinct photophysical features, different transition metals are considered individually to demonstrate particular trends regarding ligand modification within the respective groups. In summary, this review elucidates the current state-of-the-art and future potential of the versatile class of 2,2'-biimidazole based sensor chromophores.

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Section: Sensors For Small Anionssupporting

confidence: 52%

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

Rommel

Sorsche

Fleischmann

et al. 2017

Chemistry A European J

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“…Inspired by Fe(II) biimidazoline complexes which had been used successfully for investigations of ground-state PCET, 4,29,30 photoactive d 6 metal complexes of 2,2'-biimidazole were therefore investigated in the context of excited-state PCET. [31][32][33] From early studies by Haga it was known that biimidazole complexes of Ru(II) and Os(II) exhibit long-lived 3 MLCT states from which electron and proton donation occurs more readily than from the ground state. 34 Given the proximity of the N-H functions to the metal center it was hoped that deprotonation could be monitored by optical spectroscopy, and this was in fact one of the key motivations for this work.…”

Section: Photoexcited Complexes As Comined Electron/proton Donorsmentioning

confidence: 99%

Proton-Coupled Electron Transfer with Photoexcited Metal Complexes

2013

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Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)₃²⁺/Os(bpy)₃²⁺-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction.

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“…9,[26][27][28][29][30] (3) Hydrogen bonds, where the sensitizer and PCET reactant are brought together through a hydrogen bond. 3,[31][32][33][34] The use of covalent and hydrogen bonds in ES-PCET has facilitated large gains in the fundamental understanding of ES-PCET. One large convenience afforded through the latter two methods is that the removal of reactant diffusion allows direct measurement of the ES-PCET reaction rate constants.…”

Section: Introductionmentioning

confidence: 99%