Solvent Viscosity and Interrelated Effects on Electrochemiluminescence Intensity of Tris(2,2‘-bipyridyl)ruthenium(II)

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light

Efficient excited-state electron transfer between an iron(III) photosensitizer and organic electron donors was realized with green light irradiation. This advance was enabled by the use of the previously reported iron photosensitizer, [Fe(phtmeimb)₂]⁺ (phtmeimb = {phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate}, that exhibited long-lived and luminescent ligand-to-metal charge-transfer (LMCT) excited states. A benchmark dehalogenation reaction was investigated with yields that exceed 90% and an enhanced stability relative to the prototypical photosensitizer [Ru(bpy)₃]²⁺. The initial catalytic step is electron transfer from an amine to the photoexcited iron sensitizer, which is shown to occur with a large cage-escape yield. For LMCT excited states, this reductive electron transfer is vectorial and may be a general advantage of Fe(III) photosensitizers. In-depth time-resolved spectroscopic methods, including transient absorption characterization from the ultraviolet to the infrared regions, provided a quantitative description of the catalytic mechanism with associated rate constants and yields.

Interaction studies of DNA binding of ruthenium(II) mixed-ligand complexes: [Ru(phen)2(dtmi)]2+ and [Ru(phen)2(dtni)]2+

Two new ligands, 3-(pyrazin-2-yl)-as-triazino[5,6-f]-5-methoxylisatin (dtmi), 3-(pyrazin-2-yl)-as-triazino[5,6-f]-5-nitroisatin (dtni) and their ruthenium(II) complexes [Ru(phen)2(dtmi)](ClO4)2 (1) and [Ru(phen)2(dtni)](ClO4)2 (2) have been prepared and characterized by elemental analysis, FAB-MS, ES-MS and 1H NMR. The DNA-binding behaviors of complexes have been studied by spectroscopic titration, viscosity measurements, thermal denaturation and circular dichromism (CD). The results indicate that the complexes 1 and 2 interact with calf thymus DNA (CT-DNA) by intercalative mode. The DNA-binding affinity of the complexes 2 is larger than that complex 1 does.

Ruthenium(II) Complex of Hbopip: Synthesis, Characterization, pH-Induced Luminescence “Off−On−Off” Switch, and Avid Binding to DNA

A novel ruthenium(II) complex of [Ru(bpy)2(Hbopip)](ClO4)2 (in which bpy=2,2'-bipyridine, Hbopip=2-(4-benzoxazolyl)phenylimidazo[4,5-f][1,10]phenanthroline) was synthesized and characterized. The spectrophotometric pH titrations of the complex showed that it acted as a pH-induced luminescence "off-on-off" switch: a luminescence off-on switch with a luminescence enhancement factor of IpH=3.0/IpH=1.0=20 occurring over a narrow pH range of 1.00-3.00 plus a luminescence on-off switch with a luminescence enhancement factor of 3 over a pH range of 3.20-9.40. The excited-state ionization constant of the complex derived, pKa1*=3.06, is 1.36 pKa units greater than the ground-state pKa1=1.70, and pKa2*=5.01 and pKa3*=8.22 are comparable to the ground-state pKa2=5.23 and pKa3=8.22, respectively. The complex avidly bound to calf thymus DNA with a large binding constant of (1.2+/-0.3)x10(7) M-1 in buffered 50 mM NaCl, as evidenced by UV-vis and luminescence titrations, steady-state emission quenching by [Fe(CN)6]4-, DNA competitive binding with ethidium bromide, viscosity measurements, and DNA melting experiments.

Diffusivities of Tris(2,2'-bipyridyl)ruthenium inside Silica-Nanochannels Modified with Alkylsilanes

The apparent diffusion coefficients of tris(2,2'-bipyridyl)ruthenium ([Ru(bpy(3))](2+)) are estimated in silica-nanochannels which are assembled inside columnar alumina pores in an anodic alumina membrane, and are modified with alkylsilanes such as trimethylchlorosilane (C1), butyldimethylchlorosilane (C4), and dodecyldimethylchlorosilane (C12). The estimation is performed by observing the lag-time, which is defined as the time required for [Ru(bpy)(3)](2+) to diffuse through alkylsilane-modified silica-nanochannels in the alumina membrane. When ethanol is used as a solvent, the apparent diffusion coefficients of [Ru(bpy)(3)](2+) are estimated as 2.1 x 10(-10) and 3.2 x 10(-10) cm(2) s(-1) in the C1- and C4-modified silica-nanochannels, respectively. These values are about 10(4) times smaller than that obtained in bulk ethanol. Based on the experimental results on the solvent dependency of the lag-time, the hydrogen-bonding interaction between ethanol molecules is considered to be stronger in the C1- and C4-modified silica-nanochannels than in bulk ethanol, and the hydrogen-bonding interaction plays a critical role for the slow diffusivity in those nanochannels. In contrast, the apparent diffusion coefficient in the C12-modified silica-nanochannel is at least two orders of magnitude larger than those in the C1- and C4-modified silica-nanochannels. This relatively fast diffusion is most likely explained by the presence of a long alkyl chain of C12, which reduces a hindrance effect that is originates in the hydrogen-bonding interaction.