Synthesis and photochemistry of free base and zinc tetraaryl porphyrins mono-substituted with tungsten pentacarbonyl via a pyridine linker

Aspley, Catherine J.; Smith, John R. Lindsay; Perutz, Robin N.; Pursche, Daniel

doi:10.1039/b108562j

Cited by 19 publications

(6 citation statements)

References 61 publications

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“…On the basis of these relative energies, the mechanisms for populating the 3 [(d xy ) 1 (π*) 1 ] excited state following porphyrin S 1 excitation are the following: (1) singlet–singlet energy transfer from S 1 to 1 [(d xy ) 1 (π*) 1 ], followed by intersystem crossing to 3 [(d xy ) 1 (π*) 1 ]; and (2) porphyrin-centered S 1 →T 1 intersystem crossing, followed by triplet–triplet energy transfer from T 1 to 3 [(d xy ) 1 (π*) 1 ]. The former mechanism is shown below to be consistent with the observations for these compounds . Since the rate of 1 [(d xy ) 1 (π*) 1 ]→ 3 [(d xy ) 1 (π*) 1 ] intersystem crossing for 1 ( k obs > 5.5 × 10 11 s –1 , Figure S6) is appreciably faster than any of the observed kinetics for ZnPor( 1 ), the singlet–singlet energy transfer step is rate limiting in the overall S 1 → 3 [(d xy ) 1 (π*) 1 ] process.…”

Section: Discussionsupporting

confidence: 78%

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

Moravec

Hopkins

2013

J. Phys. Chem. A

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The photophysical properties of self-assembled zinc-porphyrin/tungsten-alkylidyne dyads have been investigated with the aim of determining whether the porphyrin S excited state sensitizes the tungsten-alkylidyne (3)[dπ*] state. The luminescent metalloligand W(≡CC(6)H(4)CCpy)(dppe)(2)Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) has been synthesized and shown by electronic and NMR spectroscopy to coordinate axially to ZnTPP and ZnTP(Cl)P (TP(Cl)P = tetra(p-chlorophenyl)porphyrin) via the terminal pyridyl group. Coordination of 1 to ZnPor results in partial quenching of porphyrin S(1) fluorescence and a decrease in the (3)[dπ*] excited-state lifetime of 1. Transient-absorption spectroscopy shows that fluorescence quenching occurs via intramolecular Förster resonance energy transfer from the porphyrin S(1) state to the (1)[dπ*] excited state of 1, which then undergoes rapid singlet-triplet intersystem crossing to produce the (3)[dπ*] excited state. Sensitization of the (3)[dπ*] state occurs with high overall efficiency (φ(EnT) ≈ 80%), thus strongly enhancing light harvesting for the tungsten-alkylidyne compound. The mechanism and rates of the net S(1)→(3)[dπ*] energy transfer are found to differ significantly from those for previously reported zinc-porphyrin/tungsten-alkylidyne dyads that are constructed from similar components but connected instead with covalent bonds at the porphyrin edge. Density functional theory calculations indicate that these differences are due in part to the degree of orbital mixing between the porphyrin and metal-alkylidyne subunits.

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Section: Discussionsupporting

confidence: 78%

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

Moravec

Hopkins

2013

J. Phys. Chem. A

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“…We have previously described zinc porphyrin systems linked via an amide spacer to tungsten pentacarbonyl pyridine and rhenium tricarbonyl 2,2‘-bipyridine bromide. , This design allows the porphyrin moiety to be monitored by absorption and emission spectroscopy, while the transition metal unit is revealed by its structure-sensitive CO-stretching modes. The rhenium tricarbonyl bromide complex [Re(CO) 3 BrBpy-ZnTPP] (Chart ), however, has two disadvantages: first, it does not undergo photoinduced reaction with intermolecular electron donors such as triethylamine, and second, its solubility is very low in common solvents.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Charge Separation in a Photoreactive Rhenium-Appended Porphyrin Assembly Monitored by Picosecond Transient Infrared Spectroscopy

et al. 2006

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Rhenium(bipyridine)(tricarbonyl)(picoline) units have been linked covalently to tetraphenylmetalloporphyrins of magnesium and zinc via an amide bond between the bipyridine and one phenyl substituent of the porphyrin. The resulting complexes, abbreviated as [Re(CO)(3)(Pic)Bpy-MgTPP][OTf] and [Re(CO)(3)(Pic)Bpy-ZnTPP][OTf], exhibit no signs of electronic interaction between the Re(CO)(3)(bpy) units and the metalloporphyrin units in their ground states. However, emission spectroscopy reveals solvent-dependent quenching of porphyrin emission on irradiation into the long-wavelength absorption bands localized on the porphyrin. The characteristics of the excited states have been probed by picosecond time-resolved absorption (TRVIS) spectroscopy and time-resolved infrared (TRIR) spectroscopy in nitrile solvents. The presence of the charge-separated state involving electron transfer from MgTPP or ZnTPP to Re(bpy) is signaled in the TRIR spectra by a low-frequency shift in the nu(CO) bands of the Re(CO)(3) moiety similar to that observed by spectroelectrochemical reduction. Long-wavelength excitation of [Re(CO)(3)(Pic)Bpy-MTPP][OTf] results in characteristic TRVIS spectra of the S(1) state of the porphyrin that decay with a time constant of 17 ps (M = Mg) or 24 ps (M = Zn). The IR bands of the CS state appear on a time scale of less than 1 ps (Mg) or ca. 5 ps (Zn) and decay giving way to a vibrationally excited (i.e., hot) ground state via back electron transfer. The IR bands of the precursors recover with a time constant of 35 ps (Mg) or 55 ps (Zn). The short lifetimes of the charge-transfer states carry implications for the mechanism of reaction in the presence of triethylamine.

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“…Our use of an appended bipyridine unit ensures that dissociation from the rhenium unit is not an issue, whereas dissociation becomes a concern if a metal carbonyl is coordinated to an appended pyridine. 10 Similarly, dissociation can occur when the link is made by axial coordination at the metal of the metalloporphyrin. 46,49 In this publication, we have widened the range of porphyrins to include palladium and free-base porphyrins, thus extending the range of redox potentials and emission properties.…”

Section: Introductionmentioning

confidence: 99%

“…10,12 NMR assignments were made with the aid of 2D-spectra. Photochemical reactions were performed at room temperature in an IR cell or UV cuvette using a 125 W medium-pressure mercury vapour…”

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confidence: 99%

Remote site photosubstitution in metalloporphyrin–rhenium tricarbonylbipyridine assemblies: photo-reactions of molecules with very short lived excited states

2008

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The synthesis is reported of a series of metalloporphyrins (and the corresponding free-base porphyrin), mono-meso-substituted with a bipyridyl group via an amide link at the 4-position of one phenyl group: [Re(CO)(3)(Pic)Bpy-MTPP][OTf], where M = Mg, Zn, Pd or 2H, Pic = 3-picoline, Bpy = 2,2'-bipyridine, TPP = tetraphenylporphyrin. The photochemical reactions of the assemblies with the sacrificial electron donor triethylamine have been investigated by IR spectroscopy and compared to the behaviour of analogues of the type Bpy-MTPP without rhenium. Selective long-wavelength irradiation of the metalloporphyrin unit in the presence of excess picoline leads to reduction at the rhenium bipyridine centre. In the absence of 3-picoline, the latter is not reduced, but substituted by added halide or by the THF solvent. Mechanistic analysis highlights the differences between the zinc and magnesium chelate on the one hand and the palladium porphyrin on the other. The free-base assembly, [Re(CO)(3)(Pic)Bpy-H(2)TPP][OTf] is unreactive. The zinc and magnesium porphyrin assemblies initially coordinate Et(3)N before undergoing photo-induced inner-sphere electron transfer from the triethylamine to form a charge-shifted excited state of the assembly. In contrast, the palladium-based dyad reacts via outer-sphere reductive quenching of a porphyrin-based excited state. The substitution products are postulated to form by a mechanism involving an electron-transfer chain.

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Synthesis and photochemistry of free base and zinc tetraaryl porphyrins mono-substituted with tungsten pentacarbonyl via a pyridine linker

Cited by 19 publications

References 61 publications

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

Ultrafast Charge Separation in a Photoreactive Rhenium-Appended Porphyrin Assembly Monitored by Picosecond Transient Infrared Spectroscopy

Remote site photosubstitution in metalloporphyrin–rhenium tricarbonylbipyridine assemblies: photo-reactions of molecules with very short lived excited states

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