Ana María Blanco-Rodríguez

Academy of Sciences of the Czech Republic, Praha, Hlavni mesto Praha, Czech Republic

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Publications (17)131.97 Total impact

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    ABSTRACT: Excited-state characters and dynamics of [ReCl(CO)3(3-R-1-(2-pyridyl)-imidazo[1,5-α]pyridine)] complexes (abbreviated ReGV-R, R = CH3, Ph, PhBut, PhCF3, PhNO2, PhNMe2) were investigated by pico- and nanosecond time resolved infrared spectroscopy (TRIR) and excited-state DFT and TD-DFT calculations. Near UV excitation into the lowest absorption band populates the lowest singlet state S1 that undergoes picosecond intersystem crossing (ISC) to the lowest triplet T1. Both states are initially formed hot and relax with ~20 ps lifetime. TRIR together with quantum chemical calculations reveal that S1 is predominantly a ππ* state localized at the 1-(2-pyridyl)-imidazo[1,5-α]pyridine ( = impy) ligand core, with impy→PhNO2 and PhNMe2→impy intraligand charge-transfer contributions in the case of ReGV-PhNO2 and ReGV-PhNMe2, respectively. T1 is predominantly ππ*(impy) in all cases. It follows that excited singlet and corresponding triplet states have to some extent different characters and structures even if originating nominally from the same preponderant one-electron excitations. ISC occurs with a solvent-independent (CH2Cl2, MeCN) 20-30 ps lifetime, except for ReGV-PhNMe2 (10 ps in CH2Cl2, 100 ps in MeCN). ISC is 200-300 times slower than that in analogous complexes with low-lying MLCT states. This difference is interpreted in terms of spin-orbit interaction and characters of orbitals involved in one-electron excitations that give rise to S1 and T1 states. ReGV-R present a unique case of octahedral heavy-metal complexes where the S1 lifetime is long enough to allow for separate spectroscopic characterization of singlet and triplet excited states. This study provides an insight into dynamics and intersystem crossing pathways of low-lying singlet and triplet excited states localized at bidentate ligands bound directly to a heavy metal atom. Rather long 1IL lifetimes indicate possible photonic applications of singlet excited states.
    Journal of the American Chemical Society 03/2014; · 10.68 Impact Factor
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    ABSTRACT: Re126W122CuI Pseudomonas aeruginosa azurin incorporates three redox sites, ReI(CO)3(4,7-dimethyl-1,10-phenanthroline) covalently bound at H126, the W122 indole side chain, and CuI, which are well separated in the protein fold: Re-W122(indole) = 13.1 Å; dmp-W122(indole) = 10.0 Å, Re-Cu = 25.6 Å. In view of the long intramolecular Re-Cu distance, it is surprising that CuI is oxidized in less than 50 ns after near-UV excitation of the Re chromophore. Back electron transfer (BET) regenerating CuI and ground-state ReI takes much longer (220 ns and 6 us). We show that these ET reactions occur in protein dimers, (Re126W122CuI)2, which are in equilibrium with unreactive monomers. In support of this interpretation, ET yields and kinetics are concentration-dependent and solution mass spectrometry (LILBID-MS) confirms the presence of a broad oligomer distribution with prevalent monomers and dimers; in the crystal structure, two Re126W122CuII molecules are oriented in such a way that the redox cofactors Re(dmp) and W122-indole belonging to different monomers are located at a protein-protein interface (//), where the intermolecular ET-relevant distances (Re-W122(indole) = 6.9 Å, dmp-W122(indole) = 3.5 Å, and Re-Cu = 14.0 Å) are much shorter than intramolecular ones. We propose that forward ET is accelerated by intermolecular electron hopping through a surface tryptophan: *Re//<-W122<-CuI; our kinetics analysis indicates that an equilibrium (K = 0.8-0.9) between *Re and charge-separated Re(dmp•-)(W122•+), which is established in a few ns, stores part of the excitation energy. The second ET step, intramolecular CuI oxidation, CuI->W122•+, occurs in 30 ns. The system is well coupled for forward ET but not for ReI(dmp•-)->CuII BET. Our work on interfacial electron hopping in (Re126W122CuI)2 sheds new light on redox-unit placements required for functional long-range charge separation in protein complexes.
    Journal of the American Chemical Society 09/2013; · 10.68 Impact Factor
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    ABSTRACT: X-ray absorption spectra of fac-[ReBr(CO)3(bpy)] near the Re L3- and Br K-edges were measured in a steady-state mode as well as time-resolved at 630 ps after 355 nm laser pulse excitation. Relativistic spin-orbit time-dependent density functional theory (TD-DFT) calculations account well for the shape of the near-edge absorption (the ″white line″) of the ground-state Re spectrum, assigning the lowest-lying transitions as core-to-ligand metal-to-ligand charge transfer from Re 2p3/2 into predominantly π*(bpy) molecular orbitals (MOs) containing small 5d contributions, followed in energy by transitions into π* Re(CO)3 and delocalized σ*/π* MOs. Transitions gain their intensities from Re 5d and 6s participation in the target orbitals. The 5d character is distributed over many unoccupied MOs; the 5d contribution to any single empty MO does not exceed 29%. The Br K-edge spectrum is dominated by the ionization edge and multiple scattering features, the pre-edge electronic transitions being very weak. Time-resolved spectra measured upon formation of the lowest electronic excited state show changes characteristic of simultaneous Re and Br electronic depopulation: shifts of the Re and Br edges and the Re white line to higher energies and emergence of new intense pre-edge features that are attributed by TD-DFT to transitions from Re 2p3/2 and Br 1s orbitals into a vacancy in the HOMO-1 created by electronic excitation. Experimental spectra together with quantum chemical calculations provide a direct evidence for a ReBr(CO)3 → bpy delocalized charge transfer character of the lowest excited state. Steady-state as well as time-resolved Re L3 spectra of [ReCl(CO)3(bpy)] and [Re(Etpy)(CO)3(bpy)](+) are very similar to those of the Br complex, in agreement with similar (TD) DFT calculated transition energies as well as delocalized excited-state spin densities and charge changes upon excitation.
    Inorganic Chemistry 04/2013; · 4.59 Impact Factor
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    ABSTRACT: Steady-state and picosecond time-resolved X-ray absorption spectroscopy is used to study the ground and lowest triplet states of [ReX(CO)3(bpy)]n+, X = Etpy (n=1), Cl or Br (n=0). We demonstrate that the transient spectra at both the Re L3- and Br K-edges show the emergence of a pre-edge feature, absent in the ground state spectrum, which is associated with the electron hole created in the highest occupied molecular orbital following photoexcitation. Importantly, these features have the same dynamics and this conrms previous predictions that the low lying excited states of these complexes involve a two-centre charge transfer from both the Re and the ligand, X. We also demonstrate that the DFT optimised ground and excited structures allow us to reproduce the experimental XANES and EXAFS spectra. The ground state structural renement shows that the Br atom contributes very little to the latter, while the Re-C-O scattering paths are dominant due to the so-called focusing eect. For the excited state spectrum, the Re-X bond undergoes one of the largest changes, but still remains a weak contribution to the photoinduced changes of the EXAFS spectrum.
    The Journal of Physical Chemistry A 12/2012; · 2.77 Impact Factor
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    ABSTRACT: The complex [Re(CO)(3)(dppz)(py'-OR)](+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine; py'-OR = 4-functionalized pyridine) offers IR sensitivity and can oxidize DNA directly from the excited state, making it a promising probe for the study of DNA-mediated charge transport (CT). The behavior of several covalent and noncovalent Re-DNA constructs was monitored by time-resolved IR (TRIR) and UV/visible spectroscopies, as well as biochemical methods, confirming the long-range oxidation of DNA by the excited complex. Optical excitation of the complex leads to population of MLCT and at least two distinct intraligand states. Experimental observations that are consistent with charge injection from these excited states include similarity between long-time TRIR spectra and the reduced state spectrum observed by spectroelectrochemistry, the appearance of a guanine radical signal in TRIR spectra, and the eventual formation of permanent guanine oxidation products. The majority of reactivity occurs on the ultrafast time scale, although processes dependent on slower conformational motions of DNA, such as the accumulation of oxidative damage at guanine, are also observed. The ability to measure events on such disparate time scales, its superior selectivity in comparison to other spectroscopic techniques, and the ability to simultaneously monitor carbonyl ligand and DNA IR absorption bands make TRIR a valuable tool for the study of CT in DNA.
    Journal of the American Chemical Society 08/2011; 133(34):13718-30. · 10.68 Impact Factor
  • Ana María Blanco-Rodríguez, Mike Towrie, J Sýkora, Stanislav Záliš, Antonín Vlček
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    ABSTRACT: Re(I) carbonyl-diimine complexes [Re(L-AA)(CO)(3)(N,N)](+) (N,N = bpy, phen) containing an aromatic amino acid (AA), phenylalanine (Phe), tyrosine (Tyr), or tryptophan (Trp), linked to Re by a pyridine-amido or imidazole-amido ligand L have been synthesized and their excited-state properties investigated by nanosecond time-resolved IR (TRIR) and emission spectroscopy. Near-UV optical excitation populates a Re(I)(CO)(3)→N,N (3)MLCT excited state *[Re(II)(L-AA)(CO)(3)(N,N(•-))](+). Decay to the ground state (50-300 ns lifetime) is the only excited-state deactivation process observed in the case of Phe and Tyr complexes, whereas the Trp-containing species undergo a Trp(indole)→*Re(II) electron transfer (ET) producing a charge-separated (CS) state, [Re(I)(L-Trp(•+))(CO)(3)(N,N(•-))](+). The ET occurs with a 8-40 ns lifetime depending on L, N,N, and the solvent. The CS state is characterized by ν(CO) IR bands shifted to lower wavenumbers from their respective ground-state positions and two bands at 1278 and 1497 cm(-1) tentatively attributed to Trp(•+). The amido bridge is affected by both the MLCT excitation and the subsequent ET, manifested by the shifts and intensity changes of the amide-I IR band at about 1680 cm(-1). The CS state decays to the ground state by a N,N(•-)→Trp(•+) back-ET the rates of which are comparable to those of the forward ET, 30-60 ns. This study independently demonstrates that Trp can act as an electron-hopping intermediate in photodriven ET systems based on Re-labeled proteins and supramolecules. Photoinduced ET in Trp-containing Re complexes also can be used to generate Trp(•+) and investigate its spectral properties and reactivity.
    Inorganic Chemistry 07/2011; 50(13):6122-34. · 4.59 Impact Factor
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    ABSTRACT: The [Re(I)(CO)(3)(4,7-dimethyl-1,10-phenanthroline)(histidine-124)(tryptophan-122)] complex, denoted [Re(I)(dmp)(W122)], of Pseudomonas aeruginosa azurin behaves as a single photoactive unit that triggers very fast electron transfer (ET) from a distant (2 nm) Cu(I) center in the protein. Analysis of time-resolved (ps-μs) IR spectroscopic and kinetics data collected on [Re(I)(dmp)(W122)AzM] (in which M=Zn(II), Cu(II), Cu(I); Az=azurin) and position-122 tyrosine (Y), phenylalanine (F), and lysine (K) mutants, together with excited-state DFT/time-dependent (TD)DFT calculations and X-ray structural characterization, reveal the character, energetics, and dynamics of the relevant electronic states of the [Re(I)(dmp)(W122)] unit and a cascade of photoinduced ET and relaxation steps in the corresponding Re-azurins. Optical population of [Re(I)(imidazole-H124)(CO)(3)]→dmp (1)CT states (CT=charge transfer) is followed by around 110 fs intersystem crossing and about 600 ps structural relaxation to a (3)CT state. The IR spectrum indicates a mixed Re(I)(CO)(3),A→dmp/π→π(*)(dmp) character for aromatic amino acids A122 (A=W, Y, F) and Re(I)(CO)(3)→dmp metal-ligand charge transfer (MLCT) for [Re(I)(dmp)(K122)AzCu(II)]. In a few ns, the (3)CT state of [Re(I)(dmp)(W122)AzM] establishes an equilibrium with the [Re(I)(dmp(.-))(W122(.+))AzM] charge-separated state, (3)CS, whereas the (3)CT state of the other Y, F, and K122 proteins decays to the ground state. In addition to this main pathway, (3)CS is populated by fs- and ps-W(indole)→Re(II) ET from (1)CT and the initially "hot" (3)CT states, respectively. The (3)CS state undergoes a tens-of-ns dmp(.-)→W122(.+) ET recombination leading to the ground state or, in the case of the Cu(I) azurin, a competitively fast (≈30 ns over 1.12 nm) Cu(I)→W(.+) ET, to give [Re(I)(dmp(.-))(W122)AzCu(II)]. The overall photoinduced Cu(I)→Re(dmp) ET through [Re(I)(dmp)(W122)AzCu(I)] occurs over a 2 nm distance in <50 ns after excitation, with the intervening fast (3)CT-(3)CS equilibrium being the principal accelerating factor. No reaction was observed for the three Y, F, and K122 analogues. Although the presence of [Re(dmp)(W122)AzCu(II)] oligomers in solution was documented by mass spectrometry and phosphorescence anisotropy, the kinetics data do not indicate any significant interference from the intermolecular ET steps. The ground-state dmp-indole π-π interaction together with well-matched W/W(.+) and excited-state [Re(II)(CO)(3)(dmp(.-))]/[Re(I)(CO)(3)(dmp(.-))] potentials that result in very rapid electron interchange and (3)CT-(3)CS energetic proximity, are the main factors responsible for the unique ET behavior of [Re(I)(dmp)(W122)]-containing azurins.
    Chemistry - A European Journal 04/2011; 17(19):5350-61. · 5.93 Impact Factor
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    ABSTRACT: Femto- to picosecond excited-state dynamics of the complexes [Re(L)(CO)(3)(N,N)](n) (N,N = bpy, phen, 4,7-dimethyl-phen (dmp); L = Cl, n = 0; L = imidazole, n = 1+) were investigated using fluorescence up-conversion, transient absorption in the 650-285 nm range (using broad-band UV probe pulses around 300 nm) and picosecond time-resolved IR (TRIR) spectroscopy in the region of CO stretching vibrations. Optically populated singlet charge-transfer (CT) state(s) undergo femtosecond intersystem crossing to at least two hot triplet states with a rate that is faster in Cl (∼100 fs)(-1) than in imidazole (∼150 fs)(-1) complexes but essentially independent of the N,N ligand. TRIR spectra indicate the presence of two long-lived triplet states that are populated simultaneously and equilibrate in a few picoseconds. The minor state accounts for less than 20% of the relaxed excited population. UV-vis transient spectra were assigned using open-shell time-dependent density functional theory calculations on the lowest triplet CT state. Visible excited-state absorption originates mostly from mixed L;N,N(•-) → Re(II) ligand-to-metal CT transitions. Excited bpy complexes show the characteristic sharp near-UV band (Cl, 373 nm; imH, 365 nm) due to two predominantly ππ*(bpy(•-)) transitions. For phen and dmp, the UV excited-state absorption occurs at ∼305 nm, originating from a series of mixed ππ* and Re → CO;N,N(•-) MLCT transitions. UV-vis transient absorption features exhibit small intensity- and band-shape changes occurring with several lifetimes in the 1-5 ps range, while TRIR bands show small intensity changes (≤5 ps) and shifts (∼1 and 6-10 ps) to higher wavenumbers. These spectral changes are attributable to convoluted electronic and vibrational relaxation steps and equilibration between the two lowest triplets. Still slower changes (≥15 ps), manifested mostly by the excited-state UV band, probably involve local-solvent restructuring. Implications of the observed excited-state behavior for the development and use of Re-based sensitizers and probes are discussed.
    Inorganic Chemistry 03/2011; 50(7):2932-43. · 4.59 Impact Factor
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    ABSTRACT: Ultrafast excited-state dynamics of [Re(L)(CO)(3)(bpy)](n) (L = Cl, Br, n = 0; L = 4-ethyl-pyridine (Etpy), n = 1+; bpy = 2,2'-bipyridine) have been investigated in dimethylformamide (DMF) solution by fluorescence up-conversion (FlUC) and UV-vis transient absorption (TA) with approximately 100 fs time resolution. TA was also measured in the [1-ethyl-3-methyl-imidazolium]BF(4) ionic liquid. The complexes show a very broad fluorescence band at 540-550 nm at zero time delay, which decays with 100-140 fs (depending on L) by intersystem crossing (ISC) to a pipi* intraligand ((3)IL) and a Re(L)(CO)(3) --> bpy charge-transfer ((3)CT) excited states. A second emission decay component (1.1-1.7 ps), apparent in the red part of the spectrum, is attributed to (3)IL --> (3)CT conversion, leaving phosphorescence from the lowest (3)CT state as the only emission signal at longer time delays. The triplet conversion is slower in DMF than acetonitrile, commensurate with solvation times. Full assignment of the excited-state absorption at long delay times is obtained by TD-DFT calculations on the lowest triplet state, showing that the 373 nm band is the sole diagnostics of bpy reduction in the CT excited state. Bands in the visible are due to Ligand-to-Metal-Charge-Transfer (LMCT) transitions. Time-resolved UV-vis absorption spectra exhibit a units-of-ps rise of all absorption features attributed to (3)IL --> (3)CT conversion as well as electronic and vibrational relaxation, and a approximately 15 ps rise of only the 373 nm pipi*(bpy(*-)) band, which slows down to approximately 1 ns in the ionic liquid solvent. It is proposed that this slow relaxation originates mainly from restructuring of solvent molecules that are found very close to the metal center, inserted between the ligands. The solvent thus plays a key role in controlling the intramolecular charge separation, and this effect may well be operative in other classes of metal-based molecular complexes.
    The Journal of Physical Chemistry A 06/2010; 114(22):6361-9. · 2.77 Impact Factor
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    ABSTRACT: Photoinduced relaxation processes of five structurally characterized Pseudomonas aeruginosa Re(I)(CO)(3)(alpha-diimine)(HisX) (X = 83, 107, 109, 124, 126)Cu(II) azurins have been investigated by time-resolved (ps-ns) IR spectroscopy and emission spectroscopy. Crystal structures reveal the presence of Re-azurin dimers and trimers that in two cases (X = 107, 124) involve van der Waals interactions between interdigitated diimine aromatic rings. Time-dependent emission anisotropy measurements confirm that the proteins aggregate in mM solutions (D(2)O, KP(i) buffer, pD = 7.1). Excited-state DFT calculations show that extensive charge redistribution in the Re(I)(CO)(3) --> diimine (3)MLCT state occurs: excitation of this (3)MLCT state triggers several relaxation processes in Re-azurins whose kinetics strongly depend on the location of the metallolabel on the protein surface. Relaxation is manifested by dynamic blue shifts of excited-state nu(CO) IR bands that occur with triexponential kinetics: intramolecular vibrational redistribution together with vibrational and solvent relaxation give rise to subps, approximately 2, and 8-20 ps components, while the approximately 10(2) ps kinetics are attributed to displacement (reorientation) of the Re(I)(CO)(3)(phen)(im) unit relative to the peptide chain, which optimizes Coulombic interactions of the Re(I) excited-state electron density with solvated peptide groups. Evidence also suggests that additional segmental movements of Re-bearing beta-strands occur without perturbing the reaction field or interactions with the peptide. Our work demonstrates that time-resolved IR spectroscopy and emission anisotropy of Re(I) carbonyl-diimine complexes are powerful probes of molecular dynamics at or around the surfaces of proteins and protein-protein interfacial regions.
    Journal of the American Chemical Society 07/2009; 131(33):11788-800. · 10.68 Impact Factor
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    ABSTRACT: Two sets of supramolecular rhenium carbonyl-phenanthroline complexes were prepared: fac-[Re(Cl)(CO)(3)(N,N)] and fac-[Re(Etpy)(CO)(3)(N,N)](+), where N,N is 2,9-di-anisyl-1,10-phenanthroline (dap) or two related macrocyclic ligands, where the two anisyl groups are connected by a polyether chain of different length and rigidity (m27, m30), which wraps around and above the equatorial Re(CO)(2) group. The excited-state character and relaxation dynamics of these complexes were investigated by picosecond time-resolved IR spectroscopy in the spectral region of C[triple bond, length as m-dash]O stretching vibrations, nu(CO). The results were interpreted with the aid of DFT and TD-DFT calculations of the molecular structures and electron-density redistribution upon excitation. [Re(Cl)(CO)(3)(phen-macrocycle)] in CH(2)Cl(2) have the same type of lowest excited state as analogous acyclic phen or bpy complexes, that is a mixed Re(CO)(3)-->phen and Cl-->phen MLCT/XLCT, together with some pipi*(phen) IL character. Its relaxation dynamics are qualitatively similar to those of phen or bpy complexes. However, relaxation of [Re(Cl)(CO)(3)(m30)] shows a slow kinetics component ( approximately 22 ps) which arises from confined local solvent molecules and/or from conformational movements of the flexible m30 polyether ring. In contrast, attaching anisyl groups at the 2 and 9 phen positions in [Re(Etpy)(CO)(3)(phen-macrocycle)](+) effectively "freezes" excited-state relaxation in MeCN, regardless of the presence of the macrocyclic ring. The lowest excited triplet state has a mixed MLCT/IL character. Restricting the solvent access to the excited chromophore clearly affects both the character and dynamics of the lowest excited state.
    Dalton Transactions 06/2009; · 4.10 Impact Factor
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    ABSTRACT: Energy flow in biological structures often requires submillisecond charge transport over long molecular distances. Kinetics modeling suggests that charge-transfer rates can be greatly enhanced by multistep electron tunneling in which redox-active amino acid side chains act as intermediate donors or acceptors. We report transient optical and infrared spectroscopic experiments that quantify the extent to which an intervening tryptophan residue can facilitate electron transfer between distant metal redox centers in a mutant Pseudomonas aeruginosa azurin. Cu(I) oxidation by a photoexcited Re(I)-diimine at position 124 on a histidine(124)-glycine(123)-tryptophan(122)-methionine(121) beta strand occurs in a few nanoseconds, fully two orders of magnitude faster than documented for single-step electron tunneling at a 19 angstrom donor-acceptor distance.
    Science 07/2008; 320(5884):1760-2. · 31.20 Impact Factor
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    ABSTRACT: Ultrafast electronic-vibrational relaxation upon excitation of the singlet charge-transfer b1A' state of [Re(L)(CO)3(bpy)]n (L = Cl, Br, I, n = 0; L = 4-Et-pyridine, n = 1+) in acetonitrile was investigated using the femtosecond fluorescence up-conversion technique with polychromatic detection. In addn., energies, characters, and mol. structures of the emitting states were calcd. by TD-DFT. The luminescence is characterized by a broad fluorescence band at very short times, and evolves to the steady-state phosphorescence spectrum from the a3A" state at longer times. The anal. of the data allows us to identify three spectral components. The first two are characterized by decay times t1 = 85-150 fs and t2 = 340-1200 fs, depending on L, and are identified as fluorescence from the initially excited singlet state and phosphorescence from a higher triplet state (b3A"), resp. The third component corresponds to the long-lived phosphorescence from the lowest a3A" state. In addn., it is found that the fluorescence decay time (t1) corresponds to the intersystem crossing (ISC) time to the two emissive triplet states. t2 corresponds to internal conversion among triplet states. DFT results show that ISC involves electron exchange in orthogonal, largely Re-localized, MOs, whereby the total electron momentum is conserved. Surprisingly, the measured ISC rates scale inversely with the spin-orbit coupling const. of the ligand L, but the authors find a clear correlation between the ISC times and the vibrational periods of the Re-L mode, suggesting that the latter may mediate the ISC in a strongly nonadiabatic regime.
    Journal of the American Chemical Society 06/2008; · 10.68 Impact Factor
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    ABSTRACT: Excited-state dynamics of [Re(Etpy)(CO)3(bpy)]+ was studied in three imidazolium ionic liquids by time-resolved IR and emission spectroscopy on the picosecond to nanosecond time scale. Low-lying excited states were characterized by TD-DFT calculations, which also provided molecular dipole moment vectors in the relevant electronic states. TRIR spectra in ionic liquids show initial populations of two excited states: predominantly bpy-localized 3IL and 3MLCT, characterized by nu(CO) bands shifted to lower and higher frequencies, respectively, relative to the ground state. Internal conversion of 3IL to the lowest triplet 3MLCT occurred on a time scale commensurate with solvent relaxation. The nu(CO) IR bands of the 3MLCT state undergo a dynamic shift to higher wavenumbers during relaxation. Its three-exponential kinetics were determined and attributed to vibrational cooling (units of picoseconds), energy dissipation to the bulk solvent (tens of picoseconds), and solvent relaxation, the lifetime of which increases with increasing viscosity: [EMIM]BF4 (330 ps) < [BMIM]BF4 (470 ps) < [BMIM]PF6 (1570 ps). Time-resolved phosphorescence spectra in [BMIM]PF6 show a approximately 2 ns drop in intensity due to the 3IL --> 3MLCT conversion and a dynamic Stokes shift to lower energies with a lifetime decreasing from 1.8 ns at 21 degrees C to 1.1 ns at 37 degrees C, due to decreasing viscosity of the ionic liquid. It is proposed that solvent relaxation predominantly involves collective translational motions of ions. It drives the 3IL --> 3MLCT conversion, increases charge reorganization in the lowest excited-state 3MLCT, and affects vibrational anharmonic coupling, which together cause the dynamic shift of excited-state IR bands. TRIR spectroscopy of carbonyl-diimine complexes emerges as a new way to investigate various aspects of solvation dynamics, while the use of slowly relaxing ionic liquids offers new insight into the photophysics of Re(I) carbonyl polypyridyls.
    The Journal of Physical Chemistry A 04/2008; 112(16):3506-14. · 2.77 Impact Factor
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    ABSTRACT: Excitation by high-energy light, such as that of 313 nm wavelength, induces a photochemical ligand substitution (PLS) reaction of fac-[Re(bpy)(CO)3Cl] (1a) to give the solvento complexes (OC-6-34)- and (OC-6-44)-[Re(bpy)(CO)2(MeCN)Cl] (2 and 3) in good yields. The disappearance quantum yield of 1a was 0.01+/-0.001 at 313 nm. The products were isolated, and X-ray crystallographic analysis was successfully performed for 2. Time-resolved IR measurements clearly indicated that the CO ligand dissociates with subpicosecond rates after excitation, leading to vibrationally hot photoproducts, which relax within 50-100 ps. Detailed studies of the reaction mechanism show that the PLS reaction of 1a does not proceed via the lowest vibrational level in the 3MLCT excited state. The PLS reaction gives 2 and (OC-6-24)-[Re(bpy)(CO)2(MeCN)Cl] (5) as primary products, and one of the products, 5, isomerizes to 3. This type of PLS reaction is more general, occurring in various fac-rhenium(I) diimine tricarbonyl complexes such as fac-[Re(X2bpy)(CO)3Cl] (X2bpy=4,4'-X2-bpy; X=MeO, NH2, CF3), fac-[Re(bpy)(CO)3(pyridine)]+, and fac-[Re(bpy)(CO)3(MeCN)]+. The stable photoproducts (OC-6-44)- and (OC-6-43)-[Re(bpy)(CO)2(MeCN)(pyridine)]+ and (OC-6-32)- and (OC-6-33)-[Re(bpy)(CO)2(MeCN)2]+ were isolated. The PLS reaction of rhenium tricarbonyl-diimine complexes is therefore applicable as a general synthetic method for novel dicarbonyls.
    Inorganic Chemistry 05/2007; 46(9):3531-40. · 4.59 Impact Factor
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    ABSTRACT: The triplet metal-to-ligand charge transfer ((3)MLCT) dynamics of two structurally characterized Re(I)(CO)(3)(phen)(HisX)-modified (phen = 1,10-phenanthroline; X = 83, 109) Pseudomonas aeruginosa azurins have been investigated by picosecond time-resolved infrared (TRIR) spectroscopy in aqueous (D(2)O) solution. The (3)MLCT relaxation dynamics exhibited by the two Re(I)-azurins are very different from those of the sensitizer [Re(I)(CO)(3)(phen)(im)](+) (im = imidazole). Whereas the Re(I)(CO)(3) intramolecular vibrational relaxation in Re(I)(CO)(3)(phen)(HisX)Az (4 ps) is similar to that of [Re(I)(CO)(3)(phen)(im)](+) (2 ps), the medium relaxation is much slower ( approximately 250 vs 9.5 ps); the 250-ps relaxation is attributable to reorientation of D(2)O molecules as well as structural reorganization of the rhenium chromophore and nearby polar amino acids in each of the modified proteins.
    Journal of the American Chemical Society 05/2006; 128(13):4365-70. · 10.68 Impact Factor
  • Journal of The American Chemical Society - J AM CHEM SOC. 01/2006; 128(13):4365-4370.

Publication Stats

198 Citations
131.97 Total Impact Points

Institutions

  • 2008–2013
    • Academy of Sciences of the Czech Republic
      • Ústav fyzikální chemie J. Heyrovského
      Praha, Hlavni mesto Praha, Czech Republic
    • California Institute of Technology
      • Beckman Institute
      Pasadena, CA, United States
  • 2010–2011
    • École Polytechnique Fédérale de Lausanne
      • Laboratoire de spectroscopie ultrarapide
      Lausanne, VD, Switzerland
  • 2006–2011
    • Queen Mary, University of London
      • School of Biological and Chemical Sciences
      London, ENG, United Kingdom
  • 2008–2009
    • University of London
      Londinium, England, United Kingdom