Photosensitized Generation of Singlet Oxygen from Re(I) Complexes: A Photophysical Study Using LIOAS and Luminescence Techniques

Abstract

Quantum yields and efficiencies of (1)O2 ((1)Δg) production along with photophysical properties for a number of Re(I) complexes in acetonitrile solutions are reported. Two different classes of Re(I) complexes, L(S)-CO2-Re(CO)3(bpy) (L(S) = 2-pyrazine, 2-naphthalene, 9-anthracene, 1-pyrene, 2-anthraquinone) and XRe(CO)3L (X = CF3SO3, py; L = bpy, phen), were probed as photosensitizers for (1)O2 ((1)Δg) production in air-saturated acetonitrile solutions. Depending on the nature of the Re(I) complex, the excited state responsible for the generation of (1)O2 ((1)Δg) is either a metal-to-ligand charge transfer ((3)MLCT) or a ligand centered ((3)LC) state. With L(S)-CO2-Re(CO)3(bpy) complexes, (1)O2 ((1)Δg) is produced by oxygen quenching of (3)LC states of anthracene and pyrene with high quantum yields (ΦΔ between 0.8 and 1.0), while the complexes bearing the ligands L(S) = 2-anthraquinone, 2-pyrazine, and 2-naphthalene did not yield (1)O2. XRe(CO)3L complexes generate (1)O2 ((1)Δg) mainly by oxygen quenching of their (3)MLCT luminescence with an efficiency of (1)O2 ((1)Δg) formation close to unity. Bimolecular rate constants for the quenching of the XRe(CO)3L complexes' emission by molecular oxygen range between 1 × 10(9) and 2 × 10(9) M(-1) s(-1), and they are all ≤ (1/9)kd, in good agreement with the predominance of the singlet channel in the mechanism of (1)O2 ((1)Δg) generation using these Re(I) complexes as photosensitizers. All the experimental singlet oxygen efficiencies are consistent with calorimetric and luminescence data for the studied complexes. With L(S)-CO2-Re(CO)3(bpy) complexes, calorimetric experiments were utilized in the calculation of the quantum yields of triplet formation; namely φT = 0.76 and 0.83 for the triplet states of anthracene and pyrene, respectively.

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 fact that 1 O 2 ( 1 Δ g ) is not generated with this complex is related to the low 3 MLLCT emission in those solvents. This is in agreement with our previous results in relation to the photosensitized generation of singlet oxygen from structurally related Re(I) complexes: 1 O 2 ( 1 Δ g ) generation was not observed when the luminescence quantum yields of the Re(I) complexes were as low as Φ em ∼10 −3 [23,24].…”

“…Photoacoustic measurements were performed by using a set-up already described [24]. Basically, a Q-Switched Nd:YAG laser (Surelite II, Continuum, 7 ns FWHM) operating at 355 nm was used as excitation source.…”

“…These values combined with fluorescence data and singlet oxygen quantum yield production fit the energy balance of eq. (6) [24,25]: E a = Φ em E em + α E a + Φ st E st (6) where E em is the "0-0" luminescence energy, E a is the molar energy of the laser pulse (hc/λ exc ), E st is the molar energy content of the species formed with a quantum yield Φ st which stores energy for a time longer than the heat integration time and decays with a lifetime τ. When singlet oxygen acts as storing species, the corresponding values for this species are Φ st = Φ Δ and τ = τ Δ .…”

Re(I) carbonyl complexes: Multimodal platforms for inorganic chemical biology

“…In a pioneering work, Abdel-Shafi and co-workers studied three Re carbonyl complexes bearing either a 1,10-phenanthroline, a 2,2'-bipyridine, or a benzo[h]-quinoline ligand [68] and showed that these complexes were good sensitizers for singlet oxygen. More recently, others complexes with improved properties (higher irradiation wavelengths, higher absorption coefficient…) have been developed [69]. Some of these complexes could even be embedded in a flexible polymeric silesquioxane (SSO) film while retaining their photophysical features, which opens up the possibility to use such films as biological or microbial-photoinactivating surfaces [70].…”

DNA Oxidation Photoinduced by Norharmane Rhenium(I) Polypyridyl Complexes: Effect of the Bidentate N,N′‐Ligands on the Damage Profile

“…Singlet oxygen production Details of the system used have been published previously. [41] Briefly,q uantum yields of photosensitized singlet oxygen production, F D ,w ere obtained using the third harmonic of aQ -switched Nd-YAGl aser as the excitation source (l exc = 355 nm, Surelite II-Continuum), looking at the 1270 nm 1 O 2 phosphorescence with aGe-pho-todiode (Applied Detector Corporation, resolution time of 1 ms). Measurements were performed in both air-equilibrated acetonitrile and D 2 Os olutions.…”