Photoinduced Processes in a Dendritic Zn Porphyrin Structure with a Free‐Base Porphyrin Core

Flamigni, Lucia; Talarico, Anna; Ventura, Barbara; Sooambar, Chloé; Solladié, Nathalie

doi:10.1002/ejic.200501042

Cited by 16 publications

(13 citation statements)

References 36 publications

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“…The nanosecond transient absorption spectra of ZnP‐0A – ZnP‐0C display similar characteristic features attributable to the porphyrin triplet 64. 65 In Figure 8SI, the transient spectrum of ZnP‐0B in toluene at room temperature is reported as a representative example of the whole series.…”

Section: Resultsmentioning

confidence: 93%

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

Tancini

Monti

Howes

et al. 2013

Chemistry A European J

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The synthesis, electrochemical, and photophysical properties of five multicomponent systems featuring a Zn(II) porphyrin (ZnP) linked to one or two anilino donor-substituted pentacyano- (PCBD) or tetracyanobuta-1,3-dienes (TCBD), with and without an interchromophoric bridging spacer (S), are reported: ZnP-S-PCBD (1), ZnP-S-TCBD (2), ZnP-TCBD (3), ZnP-(S-PCBD)2 (4), and ZnP-(S-TCBD)2 (5). By means of steady-state and time-resolved absorption and luminescence spectroscopy (RT and 77 K), photoinduced intramolecular energy and electron transfer processes are evidenced, upon excitation of the porphyrin unit. In systems equipped with the strongest acceptor PCBD and the spacer (1, 4), no evidence of electron transfer is found in toluene, suggesting ZnP→PCBD energy transfer, followed by ultrafast (<10 ps) intrinsic deactivation of the PCBD moiety. In the analogous systems with the weaker acceptor TCBD (2, 5), photoinduced electron transfer occurs in benzonitrile, generating a charge-separated (CS) state lasting 2.3 μs. Such a long lifetime, in light of the high Gibbs free energy for charge recombination (ΔG(CR)=-1.39 eV), suggests a back-electron transfer process occurring in the so-called Marcus inverted region. Notably, in system 3 lacking the interchromophoric spacer, photoinduced charge separation followed by charge recombination occur within 20 ps. This is a consequence of the close vicinity of the donor-acceptor partners and of a virtually activationless electron transfer process. These results indicate that the strongly electron-accepting cyanobuta-1,3-dienes might become promising alternatives to quinone-, perylenediimide-, and fullerene-derived acceptors in multicomponent modules featuring photoinduced electron transfer.

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Section: Resultsmentioning

confidence: 93%

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

Tancini

Monti

Howes

et al. 2013

Chemistry A European J

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“…[98] Both singlet-singlet and triplet-triplet energy transfer from the peripheral Zn porphyrins to the free-base porphyrin and triplettriplet annihilation have been detected. Association of bidentate bases increases the rigidity of the structure and improves the energy collection ability.…”

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confidence: 98%

Photochemical Conversion of Solar Energy

2008

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Energy is the most important issue of the 21st century. About 85% of our energy comes from fossil fuels, a finite resource unevenly distributed beneath the Earth's surface. Reserves of fossil fuels are progressively decreasing, and their continued use produces harmful effects such as pollution that threatens human health and greenhouse gases associated with global warming. Prompt global action to solve the energy crisis is therefore needed. To pursue such an action, we are urged to save energy and to use energy in more efficient ways, but we are also forced to find alternative energy sources, the most convenient of which is solar energy for several reasons. The sun continuously provides the Earth with a huge amount of energy, fairly distributed all over the world. Its enormous potential as a clean, abundant, and economical energy source, however, cannot be exploited unless it is converted into useful forms of energy. This Review starts with a brief description of the mechanism at the basis of the natural photosynthesis and, then, reports the results obtained so far in the field of photochemical conversion of solar energy. The "grand challenge" for chemists is to find a convenient means for artificial conversion of solar energy into fuels. If chemists succeed to create an artificial photosynthetic process, "... life and civilization will continue as long as the sun shines!", as the Italian scientist Giacomo Ciamician forecast almost one hundred years ago.

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“…A study on a nonameric porphyrin assembly made up of a central free-base and eight peripheral Zn porphyrins connected by flexible nucleoside linkers has evidenced the presence of several nonequilibrated conformations [46]. Both singlet-singlet and triplet-triplet energy transfer from the peripheral Zn porphyrins to the free-base porphyrin and triplet-triplet annihilation have been detected.…”

Section: Dendrimersmentioning

confidence: 99%

Light‐Harvesting Antennae

2008

Molecular Devices and Machines

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An antenna for light harvesting (Figure 6.1) is an organized multicomponent system in which several chromophoric molecular species absorb the incident light and channel the excitation energy to a common acceptor component [1]. For artificial systems, the term antenna effect was first used [2] to discuss the case of strongly emitting but weakly absorbing lanthanide ions surrounded by strongly absorbing ligands, where the luminescence of the lanthanide ion was sensitized by excitation in the ligand-centered (LC) excited states. Research in this area is still very active [3]. Antenna systems are widely used by Nature to solve the problem of light-harvesting efficiency in the photosynthetic process, where light is converted into chemical energy [4]. Collecting light by an antenna system, however, may also be useful for other purposes, such as signal amplification in luminescence sensors [5], photodynamic cancer therapy [6], and upconversion processes [7]. A large system, where an array of chromophoric units absorb light and transfer energy to a luminescent center, can also be considered a spatial and spectral energy concentrator (molecular lens) [8].The antenna effect can only be obtained in supramolecular arrays suitably organized in the dimensions of time, energy, and space. Each molecular component has to absorb the incident light, and the excited state so obtained (donor) has to transfer electronic energy to a nearby component (acceptor), before undergoing radiative or nonradiative deactivation (organization in the time dimension). For energy transfer to occur, the energy of the acceptor excited state has to be lower or, at most, equal to the energy of the excited state of the donor (organization in the energy dimension). Finally, the successive donor-to-acceptor energy-transfer steps must result in an overall energy-transfer process leading the excitation energy toward a selected component of the array (organization in the space dimension).In the course of evolution, Nature has succeeded in building up antenna systems that fully satisfy the above requirements. In green plants, such natural antennae j135 Molecular Devices and Machines. Concepts and Perspectives for the Nanoworld. 2 nd Ed.

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Photoinduced Processes in a Dendritic Zn Porphyrin Structure with a Free‐Base Porphyrin Core

Cited by 16 publications

References 36 publications

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

Photochemical Conversion of Solar Energy

Light‐Harvesting Antennae

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