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Title: On the Importance of Electronic Symmetry for Triplet State Delocalization

Abstract

The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restores the symmetry of the system, the triplet state is again found to be completely delocalized. Finally, the observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [2];  [3]; ORCiD logo [2]; ORCiD logo [1]
  1. Univ. of Oxford (United Kingdom). Centre for Advanced Electron Spin Resonance (CAESR)
  2. Duke Univ., Durham, NC (United States). Dept. of Chemistry
  3. Saint Joseph's Univ., Philadelphia, PA (United States). Dept. of Physics
Publication Date:
Research Org.:
Duke Univ., Durham, NC (United States); Univ. of Oxford, Oxford (United Kingdom)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); European Research Counsel (ERC)
OSTI Identifier:
1355067
Alternate Identifier(s):
OSTI ID: 1426483
Grant/Contract Number:  
SC0001517; 320969
Resource Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 15; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Richert, Sabine, Bullard, George, Rawson, Jeff, Angiolillo, Paul J., Therien, Michael J., and Timmel, Christiane R. On the Importance of Electronic Symmetry for Triplet State Delocalization. United States: N. p., 2017. Web. doi:10.1021/jacs.7b01204.
Richert, Sabine, Bullard, George, Rawson, Jeff, Angiolillo, Paul J., Therien, Michael J., & Timmel, Christiane R. On the Importance of Electronic Symmetry for Triplet State Delocalization. United States. doi:10.1021/jacs.7b01204.
Richert, Sabine, Bullard, George, Rawson, Jeff, Angiolillo, Paul J., Therien, Michael J., and Timmel, Christiane R. Wed . "On the Importance of Electronic Symmetry for Triplet State Delocalization". United States. doi:10.1021/jacs.7b01204.
@article{osti_1355067,
title = {On the Importance of Electronic Symmetry for Triplet State Delocalization},
author = {Richert, Sabine and Bullard, George and Rawson, Jeff and Angiolillo, Paul J. and Therien, Michael J. and Timmel, Christiane R.},
abstractNote = {The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restores the symmetry of the system, the triplet state is again found to be completely delocalized. Finally, the observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.},
doi = {10.1021/jacs.7b01204},
journal = {Journal of the American Chemical Society},
number = 15,
volume = 139,
place = {United States},
year = {2017},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/jacs.7b01204

Citation Metrics:
Cited by: 2 works
Citation information provided by
Web of Science

Figures / Tables:

Figure 1 Figure 1: Chemical structures (left), comparison of the transient cw EPR spectra (center) and proton Mims ENDOR spectra recorded at a field position corresponding to the Y− orientation (right). The EPR and ENDOR data were acquired in frozen MTHF at 20 K. Pulse lengths of 16 ns were applied inmore » the ENDOR experiments and three spectra with τ values of 120, 180, and 240 ns were averaged in all cases to yield the depicted spectra where the effect of the blind spots is compensated (cf. SI). The canonical orientations are indicated for PZn-E. The gray dotted lines indicate the magnitude of the hyperfine coupling for PZn-E and half of this value, respectively. See SI for further details.« less

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Works referencing / citing this record:

Stepwise oxidations of a nickel( ii )–iron( iii ) heterobimetallic porphyrin dimer: structure, spectroscopic and theoretical investigation
journal, January 2019

  • Kumar, Amit; Banerjee, Sayantani; Sarkar, Sabyasachi
  • Dalton Transactions, Vol. 48, Issue 27
  • DOI: 10.1039/c9dt01776c

    Figures / Tables found in this record:

      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.