Observation of a photoexcited state of a paramagnetic transition metal complex by time-resolved electron paramagnetic resonance spectroscopy

Kandrashkin, Yuri E.; Asano, Motoko S.; Est, Art van der

doi:10.1039/b602529c

Cited by 11 publications

(11 citation statements)

References 43 publications

(31 reference statements)

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“…Recently, we reported the first spinpolarized TREPR spectra of the excited states of a paramagnetic metal complex, using vanadyl octaethylporphyrin (OEPVO). 48 Here, we present a more detailed account of the TREPR data of OEPVO and the evidence supporting their assignment to the lowest trip-quartet state. We will show that the light-induced spin polarization has the same lifetime as the luminescence over a wide temperature range, and below ∼50 K, the TREPR spectra display a well-resolved hyperfine structure due to the I ) 7/2 vanadium nucleus.…”

Section: Introductionmentioning

confidence: 93%

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State

2006

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Laser flash induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting (ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra (D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm(-1) between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net polarization.

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Section: Introductionmentioning

confidence: 93%

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State

2006

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“…It has been shown that this mechanism is responsible for the decrease of the lifetime of the excited sing-doublet state in the photoexcited paramagnetic porphyrins. 20,22 It is also proposed to be one of the mechanisms of the enhanced intersystem crossing in some molecular conjugates. 11,23 It has to be noticed that the influence of the spin coherence in three-spin system was investigated earlier by Bargryansky et al 8,9 They studied the radical-ion triads in the liquid solution in the situation when one of the radicals of the singlet-born pair recombines with the encounter radical.…”

Section: ■ Quantum Yieldmentioning

confidence: 99%

“…Because of the nonequality of these interactions, the sing-doublet and trip-doublet states () become mixed, and this promotes the depopulation of the excited sing-doublet state. It has been shown that this mechanism is responsible for the decrease of the lifetime of the excited sing-doublet state in the photoexcited paramagnetic porphyrins. , It is also proposed to be one of the mechanisms of the enhanced intersystem crossing in some molecular conjugates. , …”

Section: Quantum Yieldmentioning

confidence: 99%

Influence of Spin Decoherence on the Yield of Photodriven Quantum Teleportation in Molecular Triads

Kandrashkin

2021

J. Phys. Chem. Lett.

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The evolution of spin coherences due to spin-selective recombination in the system with three unpaired electrons is discussed. It is shown that in the case of bidirectional kinetics, the decoherence processes can significantly change the quantum yield of the products. This enables one to discriminate between approaches that model spin-selective recombination but predict different decoherence rates. The rigid donor–acceptor–radical molecular triad is suggested to study the decay rate of singlet–triplet coherence. A modification of the photodriven quantum teleportation protocol is proposed to measure the quantum yields of the monoradical products.

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“…Another possible approach to achieve large optical modulations under weak incoherent photoexcitation is through the accumulation of triplet excitons in materials, which can influence various physical properties such as absorption, refractive index, and magnetic properties . Unlike the short lifetime of singlet excitons, the lifetime of triplet excitons is long because the transition from the lowest triplet excited state (T 1 ) to the ground state (S 0 ) is intrinsically forbidden .…”

Section: Introductionmentioning

confidence: 99%

Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation

Hirata

Vácha

2015

Advanced Optical Materials

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optical modulation over large areas, these changes are potentially suitable for applications such as real-time holograms, [ 6 ] light-beam modulation for continuouswave lasers, and security media.Another possible approach to achieve large optical modulations under weak incoherent photoexcitation is through the accumulation of triplet excitons in materials, which can infl uence various physical properties such as absorption, [ 10 ] refractive index, [ 11 ] and magnetic properties. [ 12 ] Unlike the short lifetime of singlet excitons, [ 13 ] the lifetime of triplet excitons is long because the transition from the lowest triplet excited state (T 1 ) to the ground state (S 0 ) is intrinsically forbidden. [ 14 ] However, the accumulation of triplet excitons has been accomplished only by irradiation with strongly amplifi ed light pulses, such as neodymium-yttriumaluminum-garnet lasers and strong fl ash lamps. [ 15 ] This is because the lifetime of triplet excitons in organic compounds is generally shorter than a millisecond at room temperature (RT) in the presence of oxygen, as they are typically deactivated by molecular motion [ 16 ] and oxygen quenching. [ 17 ] We recently discovered that various aromatic carbon materials doped in amorphous hydroxyl steroidal compounds show T 1 lifetimes longer than 1 s at RT in air because of the rigidity and high oxygen barrier of the hydroxyl steroidal host. [ 18 ] In addition, optical limiting devices that operate under weak continuous incoherent photoexcitation in the presence of oxygen through the accumulation of long-lived RT triplet excitons have been demonstrated. [ 19 ] Therefore, it is anticipated that the triplet excitons of guests can be effectively accumulated in transparent amorphous fi lms of certain host-guest materials under weak continuous incoherent excitation light to trigger a large photoresponsive transmittance change of the fi lms.Here, we demonstrate photoresponsive neutral density fi lters for the whole range of visible light using the accumulation of long-lived RT triplet excitons under weak continuous photoexcitation. Transparent host-guest fi lms composed of a secondary amino-substituted deuterated aromatic carbon material as a guest and β-estradiol as an amorphous hydroxy steroidal host are prepared as photoresponsive optical fi lters. The guest shows no ground-state absorption but effi cient broad triplet-triplet (T-T) absorption of visible light, which is caused by the moderate charge transfer (CT) characteristics of the T-T absorption. In addition, the RT triplet lifetime ( τ ) of the guest in the host Excited-state absorption of materials is caused by instantaneous accumulation of excitons when irradiated with a high-intensity laser pulse. If excitons can be accumulated by irradiation with weak continuous incoherent light at room temperature (RT) in air, then excited-state absorption can be obtained over a large area, which is potentially useful for a variety of optical applications. Here, photoresponsive transmittance control using long-lived...

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Observation of a photoexcited state of a paramagnetic transition metal complex by time-resolved electron paramagnetic resonance spectroscopy

Cited by 11 publications

References 43 publications

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State

Influence of Spin Decoherence on the Yield of Photodriven Quantum Teleportation in Molecular Triads

Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation

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