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Jianzhang Zhao - One of the best experts on this subject based on the ideXlab platform.

  • TREPR Study of the Anisotropic Spin–Lattice Relaxation Induced by Intramolecular Energy Transfer in Orthogonal BODIPY Dimers
    The Journal of Physical Chemistry, 2020
    Co-Authors: Yuri E. Kandrashkin, Xue Zhang, Andrei A. Sukhanov, Yuqi Hou, Zhijia Wang, Ya Liu, Violeta K. Voronkova, Jianzhang Zhao
    Abstract:

    The orthogonal boron dipyrromethene (BODIPY) dimers, showing efficient spin–orbit charge Transfer intersystem crossing (SOCT ISC) as promising photosensitizers for photodynamic therapy, are studied intensively with time-resolved electron paramagnetic resonance spectroscopy (TREPR). The spectral and kinetic properties of the charge recombination-induced triplet states of two BODIPY dyads have been explored by TREPR spectroscopy. The experimental data are consistent with the formation of the initial electron spin polarization by a SOCT ISC mechanism. However, the comparison of the relative populations of the triplet states shows that some other ISC channel can also be involved. The balance of the excited triplet states localized on either part of the dyads has been proved, and the Intramolecular Energy Transfer between two parts in a dyad has been established. The absolute population rates of the sublevels of the triplet state were determined. Two BODIPY dimers have different spin–lattice relaxation (SLR) times. For one of the dimers, SLR is highly anisotropic (slower at the canonical orientations). The anisotropic SLR is attributed to the fast reversible Intramolecular Energy Transfer between two subunits in the dimer with different orientations of the ZFS principal axes. The developed model of the spin evolution rationalizes all observed properties and provides a quantitative description of the time/magnetic field data sets.

  • trepr study of the anisotropic spin lattice relaxation induced by Intramolecular Energy Transfer in orthogonal bodipy dimers
    The Journal of Physical Chemistry, 2020
    Co-Authors: Yuri E. Kandrashkin, Xue Zhang, Andrei A. Sukhanov, Yuqi Hou, Zhijia Wang, Ya Liu, Violeta K. Voronkova, Jianzhang Zhao
    Abstract:

    The orthogonal boron dipyrromethene (BODIPY) dimers, showing efficient spin–orbit charge Transfer intersystem crossing (SOCT ISC) as promising photosensitizers for photodynamic therapy, are studied intensively with time-resolved electron paramagnetic resonance spectroscopy (TREPR). The spectral and kinetic properties of the charge recombination-induced triplet states of two BODIPY dyads have been explored by TREPR spectroscopy. The experimental data are consistent with the formation of the initial electron spin polarization by a SOCT ISC mechanism. However, the comparison of the relative populations of the triplet states shows that some other ISC channel can also be involved. The balance of the excited triplet states localized on either part of the dyads has been proved, and the Intramolecular Energy Transfer between two parts in a dyad has been established. The absolute population rates of the sublevels of the triplet state were determined. Two BODIPY dimers have different spin–lattice relaxation (SLR) times. For one of the dimers, SLR is highly anisotropic (slower at the canonical orientations). The anisotropic SLR is attributed to the fast reversible Intramolecular Energy Transfer between two subunits in the dimer with different orientations of the ZFS principal axes. The developed model of the spin evolution rationalizes all observed properties and provides a quantitative description of the time/magnetic field data sets.

  • Enhancing photocatalytic hydrogen evolution by Intramolecular Energy Transfer in naphthalimide conjugated porphyrins.
    Chemical communications (Cambridge England), 2018
    Co-Authors: Govardhana Babu Bodedla, Jianzhang Zhao, Yuanyuan Che, Yijiao Jiang, Jun Huang, Xunjin Zhu
    Abstract:

    Three new isomeric naphthalimide conjugated porphyrins, ZnT(p-NI)PP, ZnT(m-NI)PP and ZnT(o-NI)PP are developed for photocatalytic H2 production. The para-substituted isomer, ZnT(p-NI)PP delivered a much higher H2 production rate (ηH2) of 973 μmol g−1 h−1 compared to that of meta- and ortho-substituted isomers, ZnT(m-NI)PP (597 μmol g−1 h−1) and ZnT(o-NI)PP (54 μmol g−1 h−1), respectively. The ZnTPP produced ηH2 of 7 μmol g−1 h−1, which is 200 times lower than the ZnT(p-NI)PP. The highest ηH2 of ZnT(p-NI)PP among the isomers could be attributed to the most efficient Intramolecular Energy Transfer from the naphthalimide to the porphyrin ring which further enhanced the electron Transfer from the photo-excited porphyrin moiety to the Pt co-catalyst.

Lionel M. Raff - One of the best experts on this subject based on the ideXlab platform.

  • theoretical investigations of Intramolecular Energy Transfer rates and pathways for vinyl bromide on an ab initio potential Energy surface
    Journal of Physical Chemistry A, 2001
    Co-Authors: Asif Rahaman, Lionel M. Raff
    Abstract:

    The dynamics of Intramolecular Energy Transfer in vinyl bromide have been investigated using projection methods and results obtained from classical trajectories computed on a global potential-Energy surface (PES1) that has been fitted to a large database of energies obtained from ab initio electronic structure calculations at the MP4 level of theory with extended basis sets and experimental thermochemical data. Similar calculations on two additional potential surfaces derived from PES1 are also reported. The Intramolecular Energy Transfer dynamics obtained on these surfaces are compared with one another and with previously reported results using an empirical hybrid-type surface (EPS) fitted to thermochemical, structural, kinetic, and spectroscopic data and the results of a limited number of electronic structure calculations for the transition states. The temporal variation of the average vibrational mode energies are computed from the projected mode kinetic Energy profiles using the equipartition theorem....

  • Intramolecular Energy Transfer Rates and Pathways for Vinyl Bromide
    The Journal of Physical Chemistry, 1996
    Co-Authors: Ran Pan, Lionel M. Raff
    Abstract:

    The dynamics of Intramolecular Energy Transfer in vinyl bromide are investigated using projection methods and results obtained from classical trajectories. The method is based on the calculation of the temporal variation of a diagonal kinetic Energy matrix. Energy Transfer rates and pathways are extracted from the envelope functions of this temporal variation. Average mode energies are also obtained from these data using the virial theorem. Total Energy decay rates and the pathways of Energy flow for initial excitation of each of the 12 vibrational modes in the equilibrium configuration and in initial configurations corresponding to points in the near vicinity of the minumum-Energy structure on the optimum dividing surfaces for three-center H2 and HBr elimination are reported. The results for the equilibrium structure show that the total relaxation rate for each mode can be characterized with fair accuracy by a first-order rate law. The minimum decay rate among the 12 modes is at least 3.1 times larger th...

  • CLASSICAL Intramolecular Energy-Transfer RATES USING FOURIER TRANSFORM METHODS : FOUR-ATOM SYSTEMS
    The Journal of Physical Chemistry, 1994
    Co-Authors: Xiao Yan Chang, Donald L. Thompson, Karen L. Bintz, Lionel M. Raff
    Abstract:

    Abstract : A previously reported Fourier transform method for computation of classical Intramolecular mode-to-mode Energy-Transfer rate coefficients is extended to four-atom molecules. HONO and C2H2 are used as test cases. The method involves the Fourier transform of the time variation of a local-mode bond Energy for an ensemble of trajectories. A two-mode, collinear model is employed to demonstrate that the transform is expected to contain a series of spectral bands at frequencies corresponding to the mode-to-mode Energy-Transfer rates. Heavy-atom blocking and constrained motion methods are employed to determine the individual band assignments. The results for both HONO and C2H2 are in good accord with the total relaxation rate extracted from decay plots of the local- mode Energy. Intramolecular Energy Transfer

  • Intramolecular Energy Transfer and mode‐specific effects in unimolecular reactions of disilane
    The Journal of Chemical Physics, 1991
    Co-Authors: Harold W. Schranz, Lionel M. Raff, Donald L. Thompson
    Abstract:

    Intramolecular Energy Transfer rates and pathways in disilane Si2H6 have been investigated in detail by analysis of the envelope functions of the time variation of the uncoupled normal‐mode kinetic energies [J. Chem. Phys. 89, 5680 (1988)] and by a new method that involves the Fourier transform of the local‐mode ‘‘bond energies.’’ The results show that the total Intramolecular vibrational relaxation (IVR) rate out of a given mode is generally much faster than the total dissociation rate. However, many of the individual mode‐to‐mode rate coefficients are significantly smaller than this rate. Consequently, IVR is not globally rapid on the time scale of the reactions. The Si–Si and local modes relax over a much longer time scale than the Si–H modes. This observed decoupling of sets of internal modes is interpreted to mean that phase space is not explored ergodically on the time scale of the reactions, even at internal energies significantly greater than the dissociation thresholds. The present results are co...

Youkoh Kaizu - One of the best experts on this subject based on the ideXlab platform.

  • Highly Efficient Triplet−Triplet Intramolecular Energy Transfer and Enhanced Intersystem Crossing in Rigidly Linked Copper(II) Porphyrin−Free Base Porphyrin Hybrid Dimers
    Inorganic Chemistry, 1999
    Co-Authors: Motoko Asano-someda And, Youkoh Kaizu
    Abstract:

    Intramolecular Energy Transfer as well as excited-state relaxation of gable-type copper(II) porphyrin-free base porphyrin dimers, in which the two halves are linked via a benzene or a naphthalene, was studied by transient absorption and fluorescence spectroscopy. Photoexcitation at 532 nm of the dimer gives rise to transient absorption spectra identical to that of triplet−triplet (T−T) absorption in the free base monomer; however, the absorption intensities in the dimers are more than four times larger than that of the monomer, indicating efficient Intramolecular Energy Transfer from the copper porphyrin to the free base counterpart. Presence of pyridine in the dimer solutions decreases the initial optical densities, while the free base monomer shows no change. The decrease is ascribed to competition between Energy Transfer via triplet manifolds and quenching by pyridine in the excited trip−quartet and/or trip−doublet states of the copper porphyrin moiety. The analysis of the generated yield of the T1 fre...

  • Triplet−Triplet Intramolecular Energy Transfer in a Covalently Linked Copper(II) Porphyrin−Free Base Porphyrin Hybrid Dimer: A Time-Resolved ESR Study
    The Journal of Physical Chemistry A, 1997
    Co-Authors: Motoko Asano-someda, Takatoshi Ichino, Youkoh Kaizu
    Abstract:

    Triplet−triplet Intramolecular Energy Transfer in a covalently linked copper(II) porphyrin−free base porphyrin hybrid dimer was examined by time-resolved (TR) ESR measurements of the lowest excited triplet (T1) state of the free base porphyrin component after laser pulse excitation at 532 nm. The TRESR spectra of the free base moiety in the hybrid dimer in toluene glass at 77 K exhibit a spin polarization pattern different from that for the free base porphyrin monomer. The observed pattern for the dimer cannot be explained by any intersystem crossing (ISC) process, and it is ascribed to Intramolecular Energy Transfer that takes place from the copper porphyrin part to the free base counterpart between the triplet manifolds. On the other hand, the TRESR spectrum in 2-methyltetrahydrofuran (2-MTHF) glass, where the Energy Transfer is prohibited by the fast deactivation of the excited copper porphyrin, shows the same spin polarization pattern as that of the free base porphyrin monomer. Therefore, the copper p...

Yuri E. Kandrashkin - One of the best experts on this subject based on the ideXlab platform.

  • TREPR Study of the Anisotropic Spin–Lattice Relaxation Induced by Intramolecular Energy Transfer in Orthogonal BODIPY Dimers
    The Journal of Physical Chemistry, 2020
    Co-Authors: Yuri E. Kandrashkin, Xue Zhang, Andrei A. Sukhanov, Yuqi Hou, Zhijia Wang, Ya Liu, Violeta K. Voronkova, Jianzhang Zhao
    Abstract:

    The orthogonal boron dipyrromethene (BODIPY) dimers, showing efficient spin–orbit charge Transfer intersystem crossing (SOCT ISC) as promising photosensitizers for photodynamic therapy, are studied intensively with time-resolved electron paramagnetic resonance spectroscopy (TREPR). The spectral and kinetic properties of the charge recombination-induced triplet states of two BODIPY dyads have been explored by TREPR spectroscopy. The experimental data are consistent with the formation of the initial electron spin polarization by a SOCT ISC mechanism. However, the comparison of the relative populations of the triplet states shows that some other ISC channel can also be involved. The balance of the excited triplet states localized on either part of the dyads has been proved, and the Intramolecular Energy Transfer between two parts in a dyad has been established. The absolute population rates of the sublevels of the triplet state were determined. Two BODIPY dimers have different spin–lattice relaxation (SLR) times. For one of the dimers, SLR is highly anisotropic (slower at the canonical orientations). The anisotropic SLR is attributed to the fast reversible Intramolecular Energy Transfer between two subunits in the dimer with different orientations of the ZFS principal axes. The developed model of the spin evolution rationalizes all observed properties and provides a quantitative description of the time/magnetic field data sets.

  • trepr study of the anisotropic spin lattice relaxation induced by Intramolecular Energy Transfer in orthogonal bodipy dimers
    The Journal of Physical Chemistry, 2020
    Co-Authors: Yuri E. Kandrashkin, Xue Zhang, Andrei A. Sukhanov, Yuqi Hou, Zhijia Wang, Ya Liu, Violeta K. Voronkova, Jianzhang Zhao
    Abstract:

    The orthogonal boron dipyrromethene (BODIPY) dimers, showing efficient spin–orbit charge Transfer intersystem crossing (SOCT ISC) as promising photosensitizers for photodynamic therapy, are studied intensively with time-resolved electron paramagnetic resonance spectroscopy (TREPR). The spectral and kinetic properties of the charge recombination-induced triplet states of two BODIPY dyads have been explored by TREPR spectroscopy. The experimental data are consistent with the formation of the initial electron spin polarization by a SOCT ISC mechanism. However, the comparison of the relative populations of the triplet states shows that some other ISC channel can also be involved. The balance of the excited triplet states localized on either part of the dyads has been proved, and the Intramolecular Energy Transfer between two parts in a dyad has been established. The absolute population rates of the sublevels of the triplet state were determined. Two BODIPY dimers have different spin–lattice relaxation (SLR) times. For one of the dimers, SLR is highly anisotropic (slower at the canonical orientations). The anisotropic SLR is attributed to the fast reversible Intramolecular Energy Transfer between two subunits in the dimer with different orientations of the ZFS principal axes. The developed model of the spin evolution rationalizes all observed properties and provides a quantitative description of the time/magnetic field data sets.

Oscar L. Malta - One of the best experts on this subject based on the ideXlab platform.

  • Comment on trivalent europium lifetimes in the presence of Intramolecular Energy Transfer processes
    Journal of the Brazilian Chemical Society, 2008
    Co-Authors: Luís D. Carlos, Wagner M. Faustino, Oscar L. Malta
    Abstract:

    This work emphasizes the importance of conceptually distinguishing between lifetimes in the absence (natural lifetimes) and in the presence of Intramolecular Energy Transfer processes in lanthanide coordination compounds. It is focused on trivalent europium compounds with mixed ligands, and a case study is made on results recently reported in the literature.

  • Intramolecular Energy Transfer through charge Transfer state in lanthanide compounds: a theoretical approach.
    The Journal of chemical physics, 2005
    Co-Authors: Wagner M. Faustino, Oscar L. Malta
    Abstract:

    A theoretical approach for the Intramolecular Energy Transfer process involving the ligand-to-metal charge Transfer (LMCT) state in lanthanide compounds is developed. Considering a two-electron interaction, both the direct Coulomb and exchange interactions are taken into account, leading to expressions from which selection rules may be derived and Transfer rates may be calculated. These selection rules show that the direct Coulomb and exchange mechanisms are complementary, in the same way as obtained in previous works for the case of ligand-lanthanide ion Energy Transfer processes. An important result from numerical estimates is that the channel ligand–LMCT state is by far the dominant case, leading to Transfer rates higher than for the channel lanthanide ion–LMCT state by several orders of magnitude. The analysis of the emission quantum yield as a function of the relative Energy position of the LMCT state in a typical Eu3+ compound allows the identification of two quenching regions, the most pronounced o...

  • A theoretical approach to Intramolecular Energy Transfer and emission quantum yields in coordination compounds of rare earth ions
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1998
    Co-Authors: Oscar L. Malta, F.r. Gonçalves E Silva
    Abstract:

    Abstract A recently developed theoretical approach to the evaluation of ligand–rare earth ion Energy Transfer rates in coordination compounds is discussed in the context of a scheme for the modeling of highly luminescent rare earth compounds. This scheme is based on the joint application of the theory of 4f–4f transition rates (radiative and nonradiative), the sparkle model to describe the electronic structure of the organic part and coordination geometries of the compounds, and the present theoretical approach to Intramolecular Energy Transfer processes.