The dynamics and origin of the unrelaxed fluorescence of free-base tetraphenylporphyrin

Białkowski, Bartłomiej; Stepanenko, Yuriy; Nejbauer, Michał; Radzewicz, Czesław; Waluk, Jacek

doi:10.1016/j.jphotochem.2011.10.026

Cited by 23 publications

(25 citation statements)

References 51 publications

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“…Taking the maximum value of 6.7 kcal mol −1 (0.2 nm), we estimate that the energy of the chargeseparated PV3 + •H 2 P red state is 22.4 kcal mol −1 smaller than the absorbed photon energy at 430 nm, as shown in Scheme 2. Hence, the observed subpicosecond formation of oxidized molecular wire and reduced porphyrin implies that hole transfer occurs from vibrationally excited S 1 and possibly the S 2 state according to the picosecond lifetime of these unrelaxed levels, 38,39 P assembly provides the basis for ultrafast hole transfer to the catalyst. It is important to note that a gradient of relative permittivity further governs the transfer across the Co 3 O 4 /PV3 interface, from SiO 2 (ε r = 3.9) to Co 3 O 4 (ε r = 12.9).…”

Section: Discussionmentioning

confidence: 99%

Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

et al. 2017

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The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a CoO nanoparticle catalyst for water oxidation by a molecular wire (p-oligo(phenylenevinylene) featuring three aryl units) is investigated by transient absorption spectroscopy. The wires are covalently anchored on the CoO surface and embedded in a dense, yet ultrathin (2 nm), silica layer that separates light absorber and catalyst. The porphyrin is electrostatically adsorbed on the silica surface, and aqueous colloidal solutions of the core-shell particles are used for transient optical measurements. Pulsed optical excitation of the porphyrin results in rapid injection of the photogenerated hole onto the molecular wire and concurrent formation of reduced light absorber in less than 1 picosecond (ps). Ultrafast charge separation was monitored by transient absorption of the wire radical cation, which is given by bands in the 500 to 600 nm region and at 1130 nm, while formation of reduced porphyrin was characterized by absorption at 700 nm. Forward transfer of the hole to CoO catalyst proceeds in 255 ± 23 ps. Ultrafast transfer of positive charge from the molecular assembly to a metal oxide nanoparticle catalyst for water oxidation is unprecedented. Holes on CoO recombined with electrons of the reduced sensitizer with biphasic kinetics on a much longer time scale of ten to several hundred nanoseconds. The unusually efficient hole transfer coupling of a molecular light absorber with an Earth-abundant metal oxide catalyst by silica-embedded p-oligo(phenylenevinylene) offers an approach for integrated artificial photosystems featuring product separation on the nanoscale.

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Section: Discussionmentioning

confidence: 99%

Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

et al. 2017

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“…in solar cells, or as potential agents in photodynamic therapy 3,[15][16][17][18][19][20] . been investigated extensively, both experimentally and theoretically [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] . The absorption spectrum of porphyrins features two distinct bands, namely the very bright and rather narrow B band ("Soret band") at about 400 nm and the Q band in the region of 600 -500 nm which is of moderate intensity 38 .…”

Section: Introductionmentioning

confidence: 99%

Ultrafast photochemistry of free-base porphyrin: a theoretical investigation of B → Q internal conversion mediated by dark states

Falahati

Hamerla

Huix‐Rotllant

et al. 2018

Phys. Chem. Chem. Phys.

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We examine the mechanism of ultrafast internal conversion between the B band (Soret band) and the Q band in porphine (H2P), the prototypical free-base porphyrin, using electronic structure studies and on-the-fly surface-hopping nonadiabatic dynamics. Our study highlights the crucial role of dark states within the N band which are found to mediate B/Q state transfer, necessitating a treatment beyond Gouterman's classic four-orbital model. The sequential B → N → Q pathway dominates largely over the direct B → Q pathway which is found to be energetically unfavorable. Potential energy surface cuts and conical intersections between excited states are determined by TDDFT and validated by CASSCF/CASPT2 and XMCQDPT2 calculations. Both the static analysis and on-the-fly surface-hopping calculations suggest a pathway which involves minor structural deformations via in-plane vibrations. The B → N conversion is a barrierless adiabatic process occurring within ∼20 fs, while the subsequent N → Q conversion occurs via a conical intersection within ∼100 fs, in agreement with time-resolved experiments for porphine and related free base porphyrins. Furthermore, evidence for both sequential and direct transfer to the Qx and Qy states is obtained.

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“…More details related to this experimental setup can be found in ref. 15. For the two pulses experiments the excitation beam was separated in two pulses of the same energy using a Michelson interferometer, with a 1 mm thick 50 : 50 beam splitter (Thorlabs, BSW10R).…”

Section: Experiments and Methodsmentioning

confidence: 99%

Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experiments

Angulo

Milkiewicz

Kattnig

et al. 2017

Phys. Chem. Chem. Phys.

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The effect of multiple light excitation events on bimolecular photo-induced electron transfer reactions in liquid solution is studied experimentally. It is found that the decay of fluorescence can be up to 25% faster if a second photon is absorbed after a first cycle of quenching and recombination. A theoretical model is presented which ascribes this effect to the enrichment of the concentration of quenchers in the immediate vicinity of fluorophores that have been previously excited. Despite its simplicity, the model delivers a qualitative agreement with the observed experimental trends. The original theory by Burshtein and Igoshin (J. Chem. Phys., 2000, 112, 10930-10940) was created for continuous light excitation though. A qualitative extrapolation from the here presented pulse experiments to the continuous excitation conditions lead us to conclude that in the latter the order of magnitude of the increase of the quenching efficiency upon increasing the light intensity of excitation, must also be on the order of tens of percent. These results mean that the rate constant for photo-induced bimolecular reactions depends not only on the usual known factors, such as temperature, viscosity and other properties of the medium, but also on the intensity of the excitation light.

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The dynamics and origin of the unrelaxed fluorescence of free-base tetraphenylporphyrin

Cited by 23 publications

References 51 publications

Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

Ultrafast photochemistry of free-base porphyrin: a theoretical investigation of B → Q internal conversion mediated by dark states

Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experiments

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The dynamics and origin of the unrelaxed fluorescence of free-base tetraphenylporphyrin

Cited by 23 publications

References 51 publications

Ultrafast Charge Transfer between Light Absorber and Co3O4 Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

Ultrafast Charge Transfer between Light Absorber and Co3O4 Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

Ultrafast photochemistry of free-base porphyrin: a theoretical investigation of B → Q internal conversion mediated by dark states

Influence of the excitation light intensity on the rate of fluorescence quenching reactions: pulsed experiments

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Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane

Ultrafast Charge Transfer between Light Absorber and Co₃O₄ Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane