skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

Abstract

Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the similar to 100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculatedmore » XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.« less

Authors:
 [1];  [2];  [3];  [4];  [1];  [5];  [6];  [6];  [6];  [3];  [2];  [1]
  1. Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
  2. Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
  3. Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
  4. Physics Department, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
  5. Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
  6. LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1390845
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 138; Journal Issue: 28
Country of Publication:
United States
Language:
English

Citation Formats

Shelby, Megan L., Lestrange, Patrick J., Jackson, Nicholas E., Haldrup, Kristoffer, Mara, Michael W., Stickrath, Andrew B., Zhu, Diling, Lemke, Henrik T., Chollet, Matthieu, Hoffman, Brian M., Li, Xiaosong, and Chen, Lin X. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy. United States: N. p., 2016. Web. doi:10.1021/jacs.6b02176.
Shelby, Megan L., Lestrange, Patrick J., Jackson, Nicholas E., Haldrup, Kristoffer, Mara, Michael W., Stickrath, Andrew B., Zhu, Diling, Lemke, Henrik T., Chollet, Matthieu, Hoffman, Brian M., Li, Xiaosong, & Chen, Lin X. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy. United States. doi:10.1021/jacs.6b02176.
Shelby, Megan L., Lestrange, Patrick J., Jackson, Nicholas E., Haldrup, Kristoffer, Mara, Michael W., Stickrath, Andrew B., Zhu, Diling, Lemke, Henrik T., Chollet, Matthieu, Hoffman, Brian M., Li, Xiaosong, and Chen, Lin X. 2016. "Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy". United States. doi:10.1021/jacs.6b02176.
@article{osti_1390845,
title = {Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy},
author = {Shelby, Megan L. and Lestrange, Patrick J. and Jackson, Nicholas E. and Haldrup, Kristoffer and Mara, Michael W. and Stickrath, Andrew B. and Zhu, Diling and Lemke, Henrik T. and Chollet, Matthieu and Hoffman, Brian M. and Li, Xiaosong and Chen, Lin X.},
abstractNote = {Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the similar to 100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.},
doi = {10.1021/jacs.6b02176},
journal = {Journal of the American Chemical Society},
number = 28,
volume = 138,
place = {United States},
year = 2016,
month = 7
}
  • Complementary ultrafast techniques provide clear observation of charge hopping between metals in dinuclear complexes.
  • Ultrafast processes in photoexcited N-salicylideneaniline have been investigated with femtosecond time-resolved resonance-enhanced multiphoton ionization spectroscopy. The ion signals via the S{sub 1}(n,{pi}*) state of the enol form as well as the proton-transferred cis-keto form emerge within a few hundred femtoseconds after photoexcitation to the first S{sub 1}({pi},{pi}*) state of the enol form. This reveals that two ultrafast processes, excited-state intramolecular proton transfer (ESIPT) reaction and an internal conversion (IC) to the S{sub 1}(n,{pi}*) state, occur on a time scale less than a few hundred femtoseconds from the S{sub 1}({pi},{pi}*) state of the enol form. The rise time of the transientmore » corresponding to the production of the proton-transferred cis-keto form is within 750 fs when near the red edge of the absorption is excited, indicating that the ESIPT reaction occurs within 750 fs. The decay time of the S{sub 1}({pi},{pi}*) state of the cis-keto form is 8.9 ps by exciting the enol form at 370 nm, but it dramatically decreases to be 1.5-1.6 ps for the excitation at 365-320 nm. The decrease in the decay time has been attributed to the opening of an efficient nonradiative channel; an IC from S{sub 1}({pi},{pi}*) to S{sub 1}(n,{pi}*) of the cis-keto form promotes the production of the trans-keto form as the final photochromic products. The two IC processes may provide opposite effect on the quantum yield of photochromic products: IC in the enol form may substantially reduce the quantum yield, but IC in the cis-keto form increase it.« less
  • The early temporal evolution of the transient infrared difference spectrum of bacterial reaction centers of Rhodobacter sphaeroides between 1000 and 1600 cm{sup -1} reveals a strong 200 fs component which has not yet been detected in femtosecond experiments in the visible or near infrared region. A detailed analysis of the experimental data shows that this fast component can be explained by a considerable change of the electronic structure of the primary electron donor, the special pair, during this time. A possible explanation of the reaction relates this process with an ultrafast initial intramolecular charge separation in the special pair P.more » 40 refs., 6 figs.« less
  • A combination of transient absorption (TAS) and femtosecond stimulated Raman (FSRS) spectroscopies were used to interrogate the photo-induced nuclear relaxation dynamics of poly(3-cyclohexyl,4-methylthiophene) (PCMT). The large difference in inter-ring dihedral angles of ground and excited-state PCMT make it an ideal candidate for studying large-amplitude vibrational relaxation associated with exciton trapping. Spectral shifting in the S{sub 1} TA spectra on sub-ps timescales (110 ± 20 and 800 ± 100 fs) is similar to spectroscopic signatures of excited-state relaxation observed with related photoexcited conjugated polymers and which have been attributed to exciton localization and a combination of resonant energy transfer and torsionalmore » relaxation, respectively. Measurements made with both techniques reveal fast PCMT S{sub 1} decay and triplet formation (τ{sub S1} = 25–32 ps), which is similar to the excited-state dynamics of short oligothiophenes and highly twisted polyconjugated molecules. On ultrafast timescales FSRS of S{sub 1} PCMT offers a new perspective on the nuclear dynamics that underlie localization of excitons in photoexcited conjugated polymers: Spectral dynamics in the C=C stretching region (1400–1600 cm{sup −1}) include a red-shift of the in-phase C=C stretching frequency, as well as a change in the relative intensity of in-phase and out-of-phase stretch intensities on a timescale of ∼100 fs. Both changes indicate an ultrafast vibrational distortion that increases the conjugation length in the region of the localized excitation and are consistent with exciton self-localization or trapping. Wavelength-dependent excited-state FSRS measurements further demonstrate that the C=C stretching frequency provides a useful spectroscopic handle for interrogating the degree of delocalization in excited conjugated polymers given the selectivity achieved via resonance enhancement.« less