Improvement of the Dynamic Range of pH Sensing by Using a Luminescent Tricarbonylpolypyridylrhenium(I) Complex with Three Different Protonation Sites

Abstract

The complex [Re(4,4'-(CO(2)H)(2)-bpy)(CO)(3)(4,4'-bpy)](CF(3)SO(3)), 1 (4,4'-(CO(2)H)(2)-bpy = 4,4'-dicarboxyl-2,2'-bipyridine, 4,4'-bpy = 4,4'-bipyridine), synthesized and characterized by spectroscopic techniques, displays a strong dependence of its photophysical properties on pH. From both emission intensity and lifetime measurements at different pH values, three values for the protonation constants of the excited states have been determined (pK(a1)* = 1.8 +/- 0.1, pK(a2)* = 3.9 +/- 0.1, and pK(a3)* = 5.6 +/- 0.1). The unusual bell-shaped variations of these photophysical properties can be accounted for by the changes of energy level orderings induced by each protonation, as confirmed by time-dependent density functional theory (TD-DFT) calculations. Since the solubility, stability, and dynamic range of pH sensing by 1 have been improved with respect to similar tricarbonylpolypyridylrhenium(I) complexes, we conclude that 1 can be used as an efficient molecular switch of the on-off-on type.

Improving the Photosensitizing Properties of Ruthenium Polypyridyl Complexes Using 4-Methyl-2,2′-bipyridine-4′-carbonitrile as an Auxiliary Ligand

“…Lifetimes and transient spectra of the lowest lying 3 MLCT excited states were obtained with a laser flash photolysis setup as described previously. 10,11 Lifetimes were also determined by a time-correlated single photon counting (TCSPC) technique, with Tempro-01 apparatus from Horiba Jobin Yvon (Glasgow, U.K.), using as the excitation pulse source an ultrafast 450(±15) nm Nanoled, operating at 250 kHz. Emission was collected at the emission maximum of complexes 1−3 with a monochromator with emission bandwidth selected at 12 nm.…”

Heteroleptic Ruthenium(II) Complexes with 2,2′-Bipyridines Having Carbonitriles as Anchoring Groups for ZnO Surfaces: Syntheses, Physicochemical Properties, and Applications in Organic Solar Cells

“…Fitting of emission decay data was done using a monoexponential model function with DAS6 software package (HORIBA Jobin Yvon, Glasgow, U.K.). Transient spectra were recorded with a laser flash photolysis (LFP) setup described elsewhere. , TCSPC and LFP measurements were carried out at room temperature in deoxygenated CH 3 CN solutions. Density functional theory calculations were performed with Gaussian 03 .…”

Solvent effects on the photophysical properties of Bu4N[(4,4′-bpy)Re(CO)3(bpy-5,5′-diCOO)] complex. A combined experimental and computational study

“…The luminescence lifetime of the related complex Re(CO) 3 (4,4′-bpy) 3 + corresponding to the radiative and non-radiative decay of the MLLCT Re(CO) 3 → 4,4′-bpy is 93 ns in CH 2 Cl 2 and 439 ns in CH 3 CN [44]. On the other hand, for the [Re(4,4′-bpy)(CO) 3 (bpy-4,4′-diCOOH)] + complex in aqueous solutions, a pH dependent lifetime ranging from τ ∼ 50 ns (at pH∼1) to τ ∼ 90 ns (at pH∼10) was reported [45], though no assignment to whether it corresponded to an MLLCT Re(CO) 3 → bpy-4,4′-diCOO or a MLLCT Re(CO) 3 → 4,4′-bpy excited state was made on that report. On this basis, solvent effects on the steady state and time resolved luminescence of the Bu 4 N[(4,4′-bpy)Re(CO) 3 (bpy-5,5′-diCOO)] complex can be accounted by the coexistence of 3 MLLCT Re(CO) 3 → 4,4′-bpy , 3 MLLCT Re(CO) 3 → bpy-5,5′-diCOO and 1 IL excited states.…”

“…A major drawback, however, relies on their limited solubility in aqueous media. In fact, most of the fac-ReX(CO) 3 (α-diimine) complexes which annually appear on the literature reports are exclusively soluble in organic solvents while only a few of them can be managed in aqueous solutions at physiological pHs [14][15][16][17][18][19][20][21]. In previous work we have synthesized and characterized a water soluble fac-ReX(CO) 3 (α-diimine) complex coordinating the ligands 2,2′-bipyridine-5,5′-dicarboxylate (bpy-5,5′-diCOO) and 4,4′-bipyridine (4,4′-bpy) [22].…”