Ezequiel Wolcan

Temperature and medium effects on the photophysical properties of –Re(CO)3(2,2′-bipyridine) pendant chromophores coordinated to a poly(4-vinylpyridine) backbone

Solvent and temperature effects on the photophysical properties of the polymer {[(vpy)2-vpyRe(CO)32,2′-bipyridine] CF3SO3}n∼200 and the related monomer CF3SO3[pyRe(CO)32,2′-bipyridine] were investigated in solution by flash photolysis at 337, 351 and 355 nm and by steady state irradiations. MLCT excited states in the polymer undergo a more efficient annihilation than in the monomer. Differences between the polymer and the monomer photophysical behavior are rationalized in terms of solvent and thermal effects on the transition between rigid rod and coil structures of the Re(I)-polymer.

Solvent Dependent Switching of 3MLLCT and 1IL Luminescent States in [ClRe(CO)3(Bathocuproinedisulfonate)]2–: Spectroscopic and Computational Study

Steady state and time-resolved luminescence experiments and calorimetric studies, as well as time-dependent density functional theory calculations performed on [ClRe(CO)(3)(Bathocuproinedisulfonate)](2-), show that the photophysical properties of the Re(I) anionic complex are determined by the balance between intraligand ((1)IL) and metal-ligand-to-ligand charge transfer ((3)MLLCT) excited states. In organic solvents, (3)MLLCT states prevail and the usual expected behavior is observed: bathochromic shift of the emission maximum, a reduced luminescence quantum yield and the shortening of the excited-state lifetime upon increasing the polarity of the solvent. In addition, singlet oxygen ((1)O2) is generated with high quantum yields (Φ(Δ) ≈ 0.5 in CH(3)CN) due to the quenching of the (3)MLLCT luminescence by (3)O2. The total quenching rate constant of triplet state by oxygen, k(q), reach values between 2.2 and 2.4 × 10(9) M(-1) s(-1) for the organic solvents studied. In CH(3)CN, the fraction of triplet states quenched by O2 which yield (1)O2, f(O2)T, is nearly unity. In aqueous solution, where no singlet oxygen is generated, the luminescence of the Re(I) complex is of (1)IL character with a emission quantum yield (Φ(em)) strongly pH dependent: Φ(em,(pH=2))/Φ(em,(pH=10)) ≈ 5.6. The variation of the pH of the solution tunes the photophysical properties of the Re(I) complex by changing the relative amount of the different species existing in aqueous solutions: [ClRe(CO)3(BCS)](2-), [(OH)Re(CO)3(BCS)](2-) and [(H2O)Re(CO)3(BCS)](−). TD-DFT calculations show that the percentage of charge transfer character of the electronic transitions is substantially higher in the organic solvents than in aqueous solutions, in agreement with the increase of (1)IL character of HOMO in [(H2O)Re(CO)3(BCS)](−) relative to [ClRe(CO)3(BCS)](2-).

Temperature effects on the quenching of the 5D0→7F2 emission of Eu(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)3 by a Cu(II) macrocycle

Luminescence quenching of Eu(fod)3(fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) by a Cu(II) macrocycle was studied at 25, 35 and 45 degrees C by steady-state and flash luminescence techniques, varying the Cu(II) concentration between 0.2 and 20 mM. Experimental variation of the observed rate constant with the quencher concentration is rationalized in terms of a mechanism involving the quenching of two unequilibrated species by the Cu(II) macrocycle.

Shielding of Electron Acceptors Coordinated to Rhenium(I) by Carboxylato Groups. Intraligand and Charge‐Transfer Excited‐State Properties of fac‐(‘Anthraquinone‐2‐carboxylato')(2,2′‐bipyridine)tricarbonylrhenium (fac‐[ReI(aq‐2‐CO2)(2,2′‐bipy)(CO)3])

The photophysical and photochemical properties of (OC-6-33)-(2,2′-bipyridine-κN1,κN1′)tricarbonyl(9,10-dihydro-9,10-dioxoanthracene-2-carboxylato-κO)rhenium (fac-[ReI(aq-2-CO2)(2,2′-bipy)(CO)3]) were investigated and compared to those of the free ligand 9,10-dihydro-9,10-dioxoanthracene-2-carboxylate (=anthraquinone-2-carboxylate) and other carboxylato complexes containing the (2,2′-bipyridine)tricarbonylrhenium ([Re(2,2′-bipy)(CO)3]) moiety. Flash and steady-state irradiations of the anthraquinone-derived ligand (λexc 337 or 351 nm) and of its complex reveal that the photophysics of the latter is dominated by processes initiated in the Re-to-(2,2′-bipyridine) charge-transfer excited state and 2,2′-bipyridine- and (anthraquinone-2-carboxylato)-centered intraligand excited states. In the reductive quenching by N,N-diethylethanamine (TEA) or 2,2′,2″-nitrilotris[ethanol] TEOA, the reactive states are the 2,2′-bipyridine-centered and/or the charge-transfer excited states. The species with a reduced anthraquinone moiety is formed by the following intramolecular electron transfer, after the redox quenching of the excited state: [ReI(aq−2−CO2)(2,2′-bipy.)(CO)3]−⇌[ReI(aq−2−CO2.)(2,2′-bipy)(CO)3]− The photophysics, particularly the absence of a ReI-to-anthraquinone charge-transfer excited state photochemistry, is discussed in terms of the electrochemical and photochemical results.

On the origins of the absorption spectroscopy of pterin and Re(CO)3(pterin)(H2O) aqueous solutions. A combined theoretical and experimental study

The origins of the absorption spectroscopy of pterin and Re(CO)3(pterin)(H2O) complex as a function of pH is studied using the hybrid functional B3LYP and PBE0 in combination with 6-311++G(d,p) and LanL2TZ(f) basis sets. A natural bond analysis was performed to the principal molecular orbitals involved in the electronic transitions of the studied compounds. The low energy band of pterin, which is described as a H→L electronic transition, can be interpreted as an admixture of π→π(*), n→π(*) and n→n electronic transitions involving π(C2-N1, C6-N5, C9-C10) and n(C2) orbitals of the HOMO and π(*)(C6-N5, C7-N8) and n(C4) orbitals of the LUMO. The low energy band of Re(CO)3(pterin)(H2O) can be described as a combination of different MLLCT transitions where electron density residing on different π orbitals of carbonyl-Re bonds and lone pairs of Re is transferred to pterin moiety. Besides MLLCT transitions, IL, LLCT and LLMCT transitions contribute the absorptions of the Re(I) complex in the wavelength region corresponding to the high energy bands. The calculated electronic spectra of the acid and base forms of pterin and Re(CO)3(pterin)(H2O) were simulated from the theoretical results and compared to the experimental absorption spectra with great accuracy both in position and relative intensities of the absorption bands.