E. Wolcan

Intercalation of fac-[(4,4′-bpy)ReI(CO)3(dppz)]+, dppz = dipyridyl[3,2-a:2′3′-c]phenazine, in polynucleotides. On the UV-vis photophysics of the Re(I) intercalator and the redox reactions with pulse radiolysis-generated radicals

The intercalation of fac-[(4,4-bpy)Re(I)(CO)3(dppz)]+ (dppz = dipyridyl[3,2-a:23-c]phenazine) in polynucleotides, poly[dAdT]2 and poly[dGdC]2, where A = adenine, G = guanine, C = cytosine and T = thymine, is a major cause of changes in the absorption and emission spectra of the complex. A strong complex-poly[dAdT]2 interaction drives the intercalation process, which has a binding constant, Kb approximately 1.8 x 10(5) M(-1). Pulse radiolysis was used for a study of the redox reactions of e(-)(aq), C*H(2)OH and N3* radicals with the intercalated complex. These radicals exhibited more affinity for the intercalated complex than for the bases. Ligand-radical complexes, fac-[(4,4-bpy*)Re(I)(CO)3(dppz)] and fac-[(4,4-bpy)Re(I)(CO)3(dppz *)], were produced by e(-)(aq) and C*H(2)OH, respectively. A Re(II) species, fac-[(4,4-bpy)Re(II)(CO)3(dppz)](2+), was produced by N3* radicals. The rate of annihilation of the ligand-radical species was second order on the concentration of ligand-radical while the disappearance of the Re(II) complex induced the oxidative cleavage of the polynucleotide strand.

Bimolecular photoinduced electron transfer in the Marcus inverted region involving the [Re(CO)3(4-phenylpyridine)3]+ metal-to-ligand charge transfer excited state, amines and their corresponding radical products

Abstract Bimolecular electron transfer quenching of the metal-to-ligand charge transfer (MLCT) excited state of Re(CO) 3 (4-phenylpyridine) 3 (F 3 CSO 3 ) by amines was studied in acetonitrile at room temperature. The quenching rate constants ( κ q ) vary from 1.8 × 10 7 to 2.5 × 10 10 M −1 s −1 (diffusion limit). Moreover, the radical recombination reaction (back electron transfer) was also studied by flash photolysis. The back electron transfer rate constants range from 2.8 × 10 5 to 7.0 × 10 9 M −1 s −1 , lying below the diffusion-controlled limit. The rate constants show an inverse dependence on the driving force in the inverted region. All the data points can be fitted using a semiclassical model.

Photophysical properties of Re(CO)3L+3 (L=monoazine) complexes: Electronic delocalization effect in metal-to-ligand charge transfer excited states

The photophysical properties of the series of the [Re(CO)3L3]CF3SO3 (La4-phenylpyridine, 3-phenylpyridine, 4‐benzylpyridine, 4-(4 0 nitrobenzyl)-pyridine and 4,4 0 -bipyridine) have been studied. Emission spectral changes with temperature and biexponential decay of the luminescence both in dichloromethane fluid solution and frozen (77 K) media show two excited states, intraligand (IL) and metal-to-ligand charge transfer (MLCT) in character, emitting with intrinsic rates. Rates of MLCT emission badly correlate with the excited state-ground state energy gap. Departures from the energy gap law are rationalized in terms of excited state distortion and electronic delocalization. # 1998 Elsevier Science S.A. All rights reserved.

Photochemical and photophysical processes in fac-Re(CO)3−(4-phenylpyridine)3(CF3SO3). Steady state and flash photolysis study

Abstract The photophysics and photochemistry of fac-Re(CO)3(4-phenylpyridine)3+ were investigated by monochromatic steady state and flash photolysis. Two parallel photoprocesses, photogeneration of the emissive metal-to-ligand charge transfer (MLCT) state and photoredox dissociation in [Re(CO)3(4-phenylpyridine)22+, (4-phenylpyridine−)], were observed. In the former process, the emission originating from the lower MLCT excited state is electron transfer quenched by triethanolamine (TEOA) producing an Re(CO)3(4-phenylpyridine)3 radical and energy transfer quenched by Cu(TIM)2+ (TIM ≡ 2,3,9,10-tetramethyl-[14]-1,4,8,11-tetraene-N4). The primary species Re(CO)3(4-phenylpyridine)22+ generated in the latter photoprocess undergoes several thermal changes which finally lead to dimeric products. A third photoprocess, namely the photogeneration of the [Re(CO)3(4-phenylpyridine)22+ (4-phenylpyridine−)] species, is involved in the reduction of the copper macrocycle to Cu(TIM)+.

Solvent quenching of the 5D0 → 7F2 emission of Eu(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)3

Abstract Quenching of luminescence of Eu(fod) 3 (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5 octanedionate) has been studied in different solvents (i.e., acetonitrile, ethanol, methanol, n -butanol, 2-propanol, bencylic alcohol, chloroform, dichloromethane, 1,1-dichloroethane, 1,2 dichloroethane, carbon tetrachloride, benzene, toluene, m -and p -xilene, acetone, ciclohexanone, methylethylketone, methylpropylketone (iso), fluorobenzene, chlorobenzene, bromobenzene, ethyl ether, dioxane and tetrahydrofurane, and deuterated solvents acetonitrile (d 3 ), ethanol (d 1 ), methanol (d 4 ), benzene (d 6 ), acetone (d 6 ) and chloroform (d)). Absorption and emission spectra of the complex in the different solvents, their luminescence lifetimes at room temperature and at the boiling temperature of liquid air, so as in solid phase were measured. Evidences of different mechanisms for quenching of the luminescence is presented and discussed.

Carbon dioxide activation by ClRe(CO)3(4-phenylpyridine)2: steady state and flash photolysis study

Abstract Flash and steady state photolysis of fac-CIRe(CO) 3 (4-phpy) 2 (ph, phenyl; py, pyridine) have been studied in N 2 and CO 2 deaerated acetonitrile solutions containing triethanolamine (TEOA). Irradiations with photonic energies between 300 and 380 kJ mol −1 mostly populate the MLCT excited state which is electron transfer quenched by TEOA. The Re-containing radical ClRe(CO) 3 (4-phpy) 2 .− generated in this process reacts with CO 2 to product CO. Spectroscopic and kinetic information about this reaction is reported.

Photoinduced charge separation in R–CO2–Re(CO)3(2,2′-bipyridine) complexes. Two emitting charge transfer excited states

Excited state properties of the newly prepared complexes R–CO2–Re(CO)3(2,2′-bipy), where R–CO2− n= naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and acetate, were investigated by steady state and time resolved spectroscopy. The X-ray structure revealed that the R containing ligand is coordinated through the carboxylate group to Re(I). Results showed that two emitting excited states play a major role in the photophysics of the complexes. The fast component of the complexes luminescence was associated with the charge transfer excited state, MLCT, Re-to-2,2′-bipyridine, while experimental evidence led to the long lived component being attributed to a ligand-to-ligand charge transfer excited state. This emissive LLCT excited state can also evolve to a photodissociative state which ultimately produces the complex decarboxylation. On the other hand, the carboxylate nbridge was shown to be able to impede connection between R and the Re(CO)3(2,2′-bipy) chromophore.

Kinetic study of nickel(II) complexation by pteroylglutamic acid

The kinetics of the complexation of NiII by pteroylglutamic acid have been studied in the 545 ∘C range, the ionic strength (0.6 M) being regulated with KNO3, in the 5.5–7.0pH range, using the stopped-flow method. Under the experimental conditions two processes were observed. The faster process was detected in the millisecond range and is associated with the reaction between NiII and the ligand. The slower is observed within a few seconds. Complementary equilibrium studies were made at 25 ∘C. The results are consistent with the formation of a 1:1 complex between the reactants, and a mechanism is proposed to account for the observed behaviour. Equilibrium constants for the NiII plus pteroylglutamic acid system, as well as activation parameters, are reported.

Spectroelectrochemistry of anthraquinone2-CO2ReI(CO)3(2,2′-bipyridine) and related complexes

Abstract The UV–vis/IR spectroelectrochemistry of anthraquinoneue5f82-CO 2 ue5f8Re I (CO) 3 (2,2′-bipyridine), AQue5f82-CO 2 ue5f8Re I (CO) 3 (bpy), has been studied with a view to making comparisons between the photochemical and spectroelectrochemical findings. The in-situ spectra of the electrochemically reduced radical anions, AQ − and bpy − , were in excellent agreement with those obtained from the products of reductive quenching of the corresponding photochemically-excited states. Charge transfer between different groups within the molecule was investigated by looking at shifts in the stretching frequency of the CO ligand in response to redox processes on other moieties. The poor electronic conductivity of the AQue5f8CO 2 -group, along with the low reactivity of the MLCT Re→AQ excited state, was related to the decoupling properties of the carboxylate group.