Electronic Coupling between Two Amine Redox Sites through the 5,5′‐Positions of Metal‐Chelating 2,2′‐Bipyridines

Abstract

Electron delocalization of new mixed-valent (MV) systems with the aid of lateral metal chelation is reported. 2,2'-Bipyridine (bpy) derivatives with one or two appended di-p-anisylamino groups on the 5,5'-positions and a coordinated [Ru(bpy)(2)] (bpy = 2,2'-bipyridine), [Re(CO)(3)Cl], or [Ir(ppy)(2)] (ppy = 2-phenylpyridine) component were prepared. The single-crystal molecular structure of the bis-amine ligand without metal chelation is presented. The electronic properties of these complexes were studied and compared by electrochemical and spectroscopic techniques and DFT/TDDFT calculations. Compounds with two di-p-anisylamino groups were oxidized by a chemical or electrochemical method and monitored by near-infrared (NIR) absorption spectral changes. Marcus-Hush analysis of the resulting intervalence charge-transfer transitions indicated that electron coupling of these mixed-valent systems is enhanced by metal chelation and that the iridium complex has the largest coupling. TDDFT calculations were employed to interpret the NIR transitions of these MV systems.

Electron transfer pathways in mixed‐valence paracyclophane‐bridged bis‐triarylamine radical cations

“…Here, we use a protocol based on density‐functional theory and continuum solvent models to study the electronic and molecular structures, as well as ground‐ and excited‐state properties for a series of PC‐bridged TAA‐based MV radical cations, including several systems from Refs. [ ] The employed computational protocol (augmented here only by dispersion corrections to account for the π‐π‐interactions) has been previously validated successfully for both organic and transition‐metal MV systems close to the borderline, from both sides, between class II and class III . We expect thus a faithful description also for the PC‐bridged TAA radical cations, allowing us to a) evaluate the electronic coupling between the redox centers via the bridge, in comparison with conjugated bridges, to b) analyze the role of the linkers in the ET process by truncating them in our computational models, and to c) evaluate the role of the connection points for pseudo ‐ para and pseudo ‐ meta connected PC bridges.…”

Redox and Photochemistry of Bis(terpyridine)ruthenium(II) Amino Acids and Their Amide Conjugates – from Understanding to Applications

“…In terms of excited-state properties (emission quantum yield, excited state lifetime), a successful tpy ligand variation is the expansion of the small N-Ru-N bite angle by formally inserting a N-CH 3 fragment between the chelating pyridines of tpy to give ddpd-based amino acid derivatives [23] 2+ , [24] 2+ , and [27] 2+ (ddpd = N,NЈ-dimethyl-N,NЈ-dipyridin-2-ylpyridine-2,6-diamine). [56,100] In photophysical respects, extension of the tpy ligands by phenylene groups at the 4Ј-positions ([11] 2+ -[13] 2+ ) is rather ineffective [4Ј-(4-NH 2 -C 6 H 4 )-tpy, 4Ј-(4-ROOC-C 6 H 4 )-tpy], [60] and other ligand extensions might be envisaged in future work.…”

“…Despite the presence of only a single ddpd ligand with 88°bite angles and a tpy ligand with only 79°angles, complex [21] 2+ achieves a quantum yield of Φ = 0.45 % and a remarkably long 3 MLCT lifetime of τ = 722 ns at room temperature in solution (Table 1). [79,[101][102][103] Such a strong push-pull situation exists in complexes [23] 2+ and [24] 2+ (Figure 11), which feature an additional NH 2 group on the electron-donating ddpd ligand relative to their NH 2 -free counterparts [21] [56] In essence, the above-mentioned small 3 MLCT-1 GS energy gap, together with high-energy oscillators, is responsible for radiationless deactivation of the 3 MLCT state in [23] 2+ and [24] 2+ . In push-pull complex [22] 2+ , the two outer pyridine rings of the tpy ligand are additionally functionalized by electron-withdrawing ester groups.…”

“…[1] There is a plethora of applications of polypyridine complexes of ruthenium(II) such as dye-sensitized solar cells (DSSCs), [2][3][4] light-emitting devices, [5][6][7][8] anticancer and photodynamic therapy, [9][10][11] sensing of ions [12][13][14] and small neutral molecules, [15][16][17] energy transfer, [18,19] electron transfer and mixed valency, [20][21][22][23][24][25] triplet-triplet annihilation upconversion, [26][27][28][29] and molecular data storage. [1] There is a plethora of applications of polypyridine complexes of ruthenium(II) such as dye-sensitized solar cells (DSSCs), [2][3][4] light-emitting devices, [5][6][7][8] anticancer and photodynamic therapy, [9][10][11] sensing of ions [12][13][14] and small neutral molecules, [15][16][17] energy transfer, …”

Synthesis and characterization of ruthenium(II) complexes incorporating 4′-phenyl-terpyridine and triphenylphosphine

“…They are used as light harvesters in dye-sensitized solar cells [2][3][4], luminescent emitters in light-emitting electrochemical cells [5][6][7], potential anticancer and imaging agents in phototherapy [8][9][10], sensors for ions [11][12][13][14][15][16] and small molecules [17,18], photocatalysts for water splitting [19,20], hydrogen production [21][22][23][24], CO 2 reduction [21,23,25], and many other chemical reactions [23,[26][27][28][29], components in mixed valence systems [30][31][32][33][34][35], light upconversion systems [36][37][38][39] and molecular memory devices [40][41][42].…”