A Tripodal Ruthenium(II) Polypyridyl Complex with pH Controlled Emissive Quenching

Abstract

A tripodal podand has been prepared and complexed to ruthenium(II) creating a metal complex with C3‐symmetry and an enclosed cavity. The complex shows the anticipated enhanced emission when compared to [Ru(bipy)3]2+ in acetonitrile. The emission from this cryptand like structure is invariant to the introduction of monovalent cations in aqueous solution, but a significant drop in the emission was observed with increasing pH over a very broad pH range (3 to 12). This is attributed to an N to t2g electron transfer in the excited‐state in the unprotonated form with a transfer rate of the order of 4.2 × 105 s–1. The crystal structure indicates the inclusion of water within the cavity suggesting that the protonation of a tertiary amine can be effectively moderated by a water molecule held in close proximity within a rigid cavity.

(1,2-Azole)bis(bipyridyl)ruthenium(II) Complexes: Electrochemistry, Luminescent Properties, And Electro- And Photocatalysts for CO2 Reduction

“…One of the main aspects of interest in regard to these ligands is the presence of an acidic N-bound hydrogen. The role of acidic hydrogens in the “ cis -Ru II (bipy) 2 ” moiety has been widely explored, , and some recent studies describe the role of pH sensitive ligands, − the complexes’ behavior in anion recognition, − or their DNA binding properties, , to name but a few. However, there are very scarce reports of complexes containing the bis­(bipyridyl)­ruthenium­(II) fragment with 1,2-azole ligands.…”

Ruthenium Complexes with Protic Ligands: Influence of the Position of OH Groups and π Expansion on Luminescence and Photocytotoxicity

“…This red shift is proposed to be due to the generation of the triplet ligand-to-ligand charge transfer excited state ( 3 LLCT) by the mixing of the n , n ′-dhbp (n = 4 or 6) with the N,N ligands (bpy, phen, dop, or BPhen), as suggested by computations on the excited states of 2 , 3 , 4 , and 8 [ 11 , 26 ]. The electron donation from the deprotonated n , n ′-dhbp (namely [O 2 -bpy] 2− ) to the ancillary (N,N) ligands leads to the generation of an electron density capable of quenching the emission of the doubly deprotonated compounds by a photoinduced electron transfer mechanism (PET) followed by nonradiative decay via back electron transfer [ 12 , 40 ].…”

Intracellular pH Sensor Based on Heteroleptic Bis‐Cyclometalated Iridium(III) Complex Embedded into Block‐Copolymer Nanospecies: Application in Phosphorescence Lifetime Imaging Microscopy

“…[33][34][35][36][37] The phosphorescent complexes containing pH-responsive functions (-COOH, -NR 2 , -OH) in the ligand environment may also display the response of luminescent characteristics (intensity, lifetime) to media pH variations and thus can be used as pH sensors. [33,[38][39][40][41][42][43][44][45] However, the inherent sensitivity of the phosphorescent pH sensors to molecular oxygen inevitably results in the crosstalk between two external stimuli (O 2 -pH), the both may considerably vary in live biological objects. The examples of the phosphorescent pH sensors application in biological studies [38,39,[45][46][47][48] either demonstrate their application as on/off indicators in a certain pH interval [39,46,47] or implicitly assumed an even oxygen distribution across the sample and its pressure equal to that in the system used for the sensor quantitative calibration.…”