TY - JOUR
T1 - Photochemistry and photophysics of a Pd(II) metalloporphyrin
T2 - Re(I) tricarbonyl bipyridine molecular dyad and its activity toward the photoreduction of CO2 to CO
AU - Schneider, Jacob
AU - Vuong, Khuong Q.
AU - Calladine, James A.
AU - Sun, Xue Zhong
AU - Whitwood, Adrian C.
AU - George, Michael W.
AU - Perutz, Robin N.
N1 - Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.
PY - 2011/12/5
Y1 - 2011/12/5
N2 - The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2′-bipyridine-4′- carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO) 3(Pic)Bpy-PdTPP][PF6]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO) 3(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C6H4 group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λex = 520 nm) of [Re(CO) 3(Pic)Bpy-PdTPP][PF6] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO) 3(Pic)Bpy-PdTPP][PF6] is employed as a photocatalyst for the reduction of CO2 to CO in DMF/NEt3 solution with λex > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)3(Pic)Bpy][PF6] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO) 3(Pic)Bpy][PF6], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be ΔGox* = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO)3(Pic)Bpy-PdTPP] [PF6] was monitored using time-resolved infrared (TRIR) spectroscopy in the ν(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH2Cl2 with and without NEt3. Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm-1) and to the charge-separated state (2008, 1908 cm-1); these bands decay and the parent recovers with lifetimes of 20-50 ps. Spectra recorded on longer time scales (ns, μs, and seconds) show the growth and decay of further species with ν(CO) bands indicative of electron transfer to Re(Bpy).
AB - The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2′-bipyridine-4′- carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO) 3(Pic)Bpy-PdTPP][PF6]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO) 3(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C6H4 group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λex = 520 nm) of [Re(CO) 3(Pic)Bpy-PdTPP][PF6] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO) 3(Pic)Bpy-PdTPP][PF6] is employed as a photocatalyst for the reduction of CO2 to CO in DMF/NEt3 solution with λex > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)3(Pic)Bpy][PF6] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO) 3(Pic)Bpy][PF6], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be ΔGox* = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO)3(Pic)Bpy-PdTPP] [PF6] was monitored using time-resolved infrared (TRIR) spectroscopy in the ν(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH2Cl2 with and without NEt3. Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm-1) and to the charge-separated state (2008, 1908 cm-1); these bands decay and the parent recovers with lifetimes of 20-50 ps. Spectra recorded on longer time scales (ns, μs, and seconds) show the growth and decay of further species with ν(CO) bands indicative of electron transfer to Re(Bpy).
UR - http://www.scopus.com/inward/record.url?scp=82355187838&partnerID=8YFLogxK
U2 - 10.1021/ic200243y
DO - 10.1021/ic200243y
M3 - Article
C2 - 22043811
AN - SCOPUS:82355187838
SN - 0020-1669
VL - 50
SP - 11877
EP - 11889
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 23
ER -