Photosolvolysis of <i>cis</i>-[Ru(α-diimine)₂(4-aminopyridine)₂]²⁺ Complexes: Photophysical, Spectroscopic, and Density Functional Theory Analysis

The photochemical and photophysical properties of the <i>cis</i>-[Ru^II(α-diimine)₂(4-APy)₂]²⁺ complexes, where α-diimine = 1,10-phenanthroline (phen) and 4-APy = 4-aminopyridine <b>I</b>, 4,7-diphenyl-1,10-phenanthroline (Ph₂phen) <b>II</b>, 2,2′-bipyridine (bpy) <b>III</b>, and 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy) <b>IV</b>, are reported. The four complexes were characterized using high-performance liquid chromatography, ¹H NMR, UV–visible, emission, and transient absorption spectroscopy. Upon photolysis in acetonitrile solution these complexes undergo 4-APy dissociation to give the monoacetonitrile complex (for <b>II</b>, <b>III</b>, and <b>IV)</b> or the bis­(acetonitrile) complex (for <b>I</b>). A fairly wide range of excitation wavelengths (from 420 to 580 nm) were employed to explore the photophysics of these systems. Quantum yields and transient spectra are provided. Density functional theory (DFT) and time-dependent DFT analysis of singlet and triplet excited states facilitated our understanding of the photochemical behavior. A detailed assessment of the geometric and electronic structures of the lowest energy spin triplet charge transfer state (³MLCT) and spin triplet metal centered state (³MC) (dπ → σ* transitions) for species <b>I–IV</b> is presented. A second, previously unobserved, and nondissociative, ³MC state is identified and is likely involved in the primary step of photodissociation. This new ³MC state may indeed play a major role in many other photodissociation processes

Modulation of the Excited States of Ruthenium(II)-perylene Dyad to Access Near-IR Luminescence, Long-Lived Perylene Triplet State and Singlet Oxygen Photosensitization

Herein, we present a novel ruthenium(II)-perylene dyad (RuPDI-Py) that combines the photophysical properties of pyrrolidine-substituted perylene diimide (PDI-Py) and the ruthenium(II) polypyridine complex [Ru(phen)3]2+. A comprehensive study of excited-state dynamics was carried out using time-resolved and steady-state methods in a dimethyl sulfoxide solution. The RuPDI-Py dyad demonstrated excitation wavelength-dependent photophysical behavior. Upon photoexcitation above 600 nm, the dyad exclusively exhibits the near-infrared (NIR) fluorescence of the 1PDI-Py state at 785 nm (τfl = 1.50 ns). In contrast, upon photoexcitation between 350 and 450 nm, the dyad also exhibits a photoinduced electron transfer from the {[Ru(phen)3]2+} moiety to PDI-Py, generating the charge-separated intermediate state {Ru(III)-(PDI-Py)•–} (4 μs). This state subsequently decays to the long-lived triplet excited state 3PDI-Py (36 μs), which is able to sensitize singlet oxygen (1O2). Overall, tuning 1O2 photoactivation or NIR fluorescence makes RuPDI-Py a promising candidate for using absorbed light energy to perform the desired functions in theranostic applications

Luminescent Ruthenium Complexes for Theranostic Applications

The water-soluble and visible luminescent complexes <i>cis-</i>[Ru­(L-L)₂(L)₂]²⁺ where L-L = 2,2-bipyridine and 1,10-phenanthroline and L= imidazole, 1-methylimidazole, and histamine have been synthesized and characterized by spectroscopic techniques. Spectroscopic (circular dichroism, saturation transfer difference NMR, and diffusion ordered spectroscopy NMR) and isothermal titration calorimetry studies indicate binding of <i>cis-</i>[Ru­(phen)₂(ImH)₂]²⁺ and human serum albumin occurs via noncovalent interactions with <i>K</i>_b = 9.8 × 10⁴ mol^–1 L, Δ<i>H</i> = −11.5 ± 0.1 kcal mol^–1, and <i>T</i>Δ<i>S</i> = −4.46 ± 0.3 kcal mol^–1. High uptake of the complex into HCT116 cells was detected by luminescent confocal microscopy. Cytotoxicity of <i>cis-</i>[Ru­(phen)₂(ImH)₂]²⁺ against proliferation of HCT116p53^+/+ and HCT116p53^–/– shows IC₅₀ values of 0.1 and 0.7 μmol L^–1. Flow cytometry and western blot indicate RuphenImH mediates cell cycle arrest in the G1 phase in both cells and is more prominent in p53^+/+. The complex activates proapoptotic PARP in p53^–/–, but not in p53^+/+. A cytostatic mechanism based on quantification of the number of cells during the time period of incubation is suggested

Luminescent Ruthenium Complexes for Theranostic Applications

The water-soluble and visible luminescent complexes <i>cis-</i>[Ru­(L-L)₂(L)₂]²⁺ where L-L = 2,2-bipyridine and 1,10-phenanthroline and L= imidazole, 1-methylimidazole, and histamine have been synthesized and characterized by spectroscopic techniques. Spectroscopic (circular dichroism, saturation transfer difference NMR, and diffusion ordered spectroscopy NMR) and isothermal titration calorimetry studies indicate binding of <i>cis-</i>[Ru­(phen)₂(ImH)₂]²⁺ and human serum albumin occurs via noncovalent interactions with <i>K</i>_b = 9.8 × 10⁴ mol^–1 L, Δ<i>H</i> = −11.5 ± 0.1 kcal mol^–1, and <i>T</i>Δ<i>S</i> = −4.46 ± 0.3 kcal mol^–1. High uptake of the complex into HCT116 cells was detected by luminescent confocal microscopy. Cytotoxicity of <i>cis-</i>[Ru­(phen)₂(ImH)₂]²⁺ against proliferation of HCT116p53^+/+ and HCT116p53^–/– shows IC₅₀ values of 0.1 and 0.7 μmol L^–1. Flow cytometry and western blot indicate RuphenImH mediates cell cycle arrest in the G1 phase in both cells and is more prominent in p53^+/+. The complex activates proapoptotic PARP in p53^–/–, but not in p53^+/+. A cytostatic mechanism based on quantification of the number of cells during the time period of incubation is suggested