Triplet energy transfers in electrostatic host-guest ...
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| Title | Triplet energy transfers in electrostatic host-guest assemblies of unsaturated organometallic cluster cations and carboxylate-containing porphyrin pigments. |
| Author(s) | S. Aly, C. Ayed, C. Stern, R. Guilard, A. Abd-El-Aziz, P. Harvey |
| Journal | Section Title: Optical, Electron, and Mass Spectroscopy and Other Related Properties, Inorganic Chemistry (Washington, DC, United States) |
| Date | 2008 |
| Volume | 47 |
| Issue | 21 |
| Start page | 9930 |
| End page | 9940 |
| Abstract | The unsatd. cyclic [M3(dppm)3(CO)]2+ clusters (M = Pt, Pd; dppm = Ph2P-CH2PPh2; such as PF6- salt) exhibit a cavity formed by the six dppm-Ph groups placed like a picket fence above the unsatd. triangular M3 dicationic center. Electrostatic interactions of the M3+ units inside this cavity with the carboxylate anion RCO2- [R = tetraphenylporphyrinatozinc(II), ZnTPP; p-phenyltritolylporphyrinatozinc(II), ZnTTPP; p-phenyltritolylporphyrinatopalladium(II), PdTTPP] form dyads for through-space triplet energy transfers. The binding consts. are ∼20,000 M-1 in all six cases (298 K). The energy diagram built upon absorption and emission spectra at 298 and 77 K places the [Pt3(dppm)3(CO)]2+ and [Pd3(dppm)3(CO)]2+ as triplet energy donors, resp., with respect to the ZnTPPCO2-, ZnTTPPCO2-, and PdTTPPCO2- pigments, which act as acceptors. Evidence for energy transfer is provided by the transient absorption spectra at 298 K, where triplet-triplet absorption bands of the metalloporphyrin chromophores are depicted at all time (at 298 K) with total absence of the charge-sepd. state in the nanosecond to microsecond time scale. Rates for energy transfer (ranging in the 104 s-1 time scale) are extd. from the emission lifetimes of the [Pt3(dppm)3(CO)]2+ donor in the free chromophore and the host-guest assemblies. The emission intensity of [Pd3(dppm)3(CO)]2+ is too weak to measure its spectrum and emission lifetime in the presence of the strongly luminescent metalloporphyrin-contg. materials. For the [Pd3(dppm)3(CO)]2+···metalloporphyrin dyads, evidence for fluorescence and phosphorescence lifetime quenching of the porphyrin chromophore at 298 K is provided. These quenchings, exhibiting rates of 104 (triplet) and 108 s-1 (singlet), are attributed to a photoinduced electron transfer from the metalloporphyrin to the cluster due to the low redn. potential. [on SciFinder(R)] |
| DOI | 10.1021/ic801006g |
| ISSN | 0020-1669 |
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