Gustavo T. Ruiz

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-).

Morphology and radical reactions of Cu(II) and Co(II) sulfonated phthalocyanines covalently linked to poly(ethyleneamide)

The tetrasulfonated CuII(tspc)4-, tspc = 4,4′,4″,4‴-phthalocyaninetetrasulfonate, and the trisulfonated CoII(trspc)3-, trspc = n,n′,n″-phthalocyanine-trisulfonate and n, n′ and n″ indicate the sulfonated positions of the various isomers, were covalently linked to a polyethyleneimine, Mn ~ 10000 and Mw ~ 25000, backbone. A fraction of the amine groups in a strand was converted to CuIIpc(-SO3)3(-SO2N<)\3- or CoIIpc(-SO3)2(-SO2N<)\2- pendants and the remaining were acetylated. Strands of the polymers, poly(K3CuIItspc) and poly(K2CoIItrspc), formed spherical bundles with diameters ~1000 nm for poly(K3CuIItspc) and ~100 nm for poly(K2CoIItrspc). The stability of the bundles is metal-dependent. Poly(K2CoIItrspc) forms the most stable bundles with respect to hydrolytic and redox reactions. ESR and optical spectroscopies as well as reactions of the pendants with pulse radiolytically generated radicals, namely e-sol, C•H2OH, (CH3)2COHC•H2, CO2•-, N3• and SO4•-, revealed a distribution of pendants between isolated and aggregated forms in a bundle. The reduction of the Cu(II) to Cu(I) in aqueous solutions of the poly(K3CuIItspc) was associated with pendants present in a mostly hydrophobic environment. Unstable phthalocyanine pendants with CoIII-carbon bonds are formed when CoIIpc(-SO3)2(-SO2N<)\2- reacted with C-centered radicals, (CH3)2COHC•H2 and C•H2OH. The species with CoIII-carbon bonds were precursors to the formation of CoIpc(-SO3)2(-SO2N<)\3- pendants. The redox reactions of the pendants in these polymers are compared with those of K4CuIItspc and K3CoIItrspc.

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.