Investigation of the Redox and Acid-Base properties of TCNQF and TCNQF2: Electrochemistry, Vibrational Spectroscopy, and Substituent Effects

Nguyen Vo, Naomi L. Haworth, Alan M. Bond, Lisandra L. Martin

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The electrochemistry and acid-base chemistry of TCNQF and TCNQF2 (TCNQ=7,7,8,8-tetracyanoquinodimethane) are described, and the results are compared to those reported previously for TCNQ and TCNQF4. In acetonitrile solution, both mono- and di-fluorinated TCNQ derivatives show two well-resolved, diffusion-controlled chemically and electrochemically reversible one-electron-transfer processes under the conditions of cyclic voltammetry. The reversible potentials of the mono- and difluoro-TCNQ were determined for both the monoanionic and dianionic processes, that is, TCNQF0/1−/2− and TCNQF2 0/1−/2−. A Hammett plot shows a linear relationship of the potential differences between the three fluorinated derivatives and TCNQ with the sum of the Hammett constants for fluoro substitution. A significant positive shift in the reversible potential is found by increasing the number of fluoro substituents. Although the first TCNQFn 0/1− (n=1,2) reduction process is not affected by addition of trifluoroacetic acid (TFA), the dianions are more basic and rapidly protonate to form H2TCNQFn. This explains the significant change detected in the electrochemistry of the second TCNQFn 1−/2− redox process. The addition of TFA to solutions of the monoanionic form also gives rise to the disproportionation of TCNQFn 1− to TCNQFn and H2TCNQFn, as proven electrochemically and spectroscopically. Furthermore, a higher number of fluoro substituents results in the reduced form of the molecule being more stable, as evidenced by both UV/Vis spectra and voltammetric measurements. Finally, we performed DFT calculations for TCNQF2 and TCNQF2 to produce a spectroscopic library of characteristic IR and Raman bands for these species. These data are used for comparisons with earlier calculations for TCNQF4, and we report the experimental and calculated infrared and Raman spectra for TCNQF and TCNQF2. The vibrational frequencies of the trifluorinated species, TCNQF3, were also calculated to complete the series.

Original languageEnglish
Pages (from-to)1173-1185
Number of pages13
JournalChemElectroChem
Volume5
Issue number8
DOIs
Publication statusPublished - 1 Apr 2018

Keywords

  • acid-base chemistry
  • density functional theory
  • electrochemistry
  • fluorinated-TCNQ
  • vibrational spectroscopy

Cite this

@article{fcf2e2d1e01c45608825e611c46c0701,
title = "Investigation of the Redox and Acid-Base properties of TCNQF and TCNQF2: Electrochemistry, Vibrational Spectroscopy, and Substituent Effects",
abstract = "The electrochemistry and acid-base chemistry of TCNQF and TCNQF2 (TCNQ=7,7,8,8-tetracyanoquinodimethane) are described, and the results are compared to those reported previously for TCNQ and TCNQF4. In acetonitrile solution, both mono- and di-fluorinated TCNQ derivatives show two well-resolved, diffusion-controlled chemically and electrochemically reversible one-electron-transfer processes under the conditions of cyclic voltammetry. The reversible potentials of the mono- and difluoro-TCNQ were determined for both the monoanionic and dianionic processes, that is, TCNQF0/1−/2− and TCNQF2 0/1−/2−. A Hammett plot shows a linear relationship of the potential differences between the three fluorinated derivatives and TCNQ with the sum of the Hammett constants for fluoro substitution. A significant positive shift in the reversible potential is found by increasing the number of fluoro substituents. Although the first TCNQFn 0/1− (n=1,2) reduction process is not affected by addition of trifluoroacetic acid (TFA), the dianions are more basic and rapidly protonate to form H2TCNQFn. This explains the significant change detected in the electrochemistry of the second TCNQFn 1−/2− redox process. The addition of TFA to solutions of the monoanionic form also gives rise to the disproportionation of TCNQFn 1− to TCNQFn and H2TCNQFn, as proven electrochemically and spectroscopically. Furthermore, a higher number of fluoro substituents results in the reduced form of the molecule being more stable, as evidenced by both UV/Vis spectra and voltammetric measurements. Finally, we performed DFT calculations for TCNQF2 and TCNQF2 to produce a spectroscopic library of characteristic IR and Raman bands for these species. These data are used for comparisons with earlier calculations for TCNQF4, and we report the experimental and calculated infrared and Raman spectra for TCNQF and TCNQF2. The vibrational frequencies of the trifluorinated species, TCNQF3, were also calculated to complete the series.",
keywords = "acid-base chemistry, density functional theory, electrochemistry, fluorinated-TCNQ, vibrational spectroscopy",
author = "Nguyen Vo and Haworth, {Naomi L.} and Bond, {Alan M.} and Martin, {Lisandra L.}",
year = "2018",
month = "4",
day = "1",
doi = "10.1002/celc.201701387",
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pages = "1173--1185",
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Investigation of the Redox and Acid-Base properties of TCNQF and TCNQF2 : Electrochemistry, Vibrational Spectroscopy, and Substituent Effects. / Vo, Nguyen; Haworth, Naomi L.; Bond, Alan M.; Martin, Lisandra L.

In: ChemElectroChem, Vol. 5, No. 8, 01.04.2018, p. 1173-1185.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Investigation of the Redox and Acid-Base properties of TCNQF and TCNQF2

T2 - Electrochemistry, Vibrational Spectroscopy, and Substituent Effects

AU - Vo, Nguyen

AU - Haworth, Naomi L.

AU - Bond, Alan M.

AU - Martin, Lisandra L.

PY - 2018/4/1

Y1 - 2018/4/1

N2 - The electrochemistry and acid-base chemistry of TCNQF and TCNQF2 (TCNQ=7,7,8,8-tetracyanoquinodimethane) are described, and the results are compared to those reported previously for TCNQ and TCNQF4. In acetonitrile solution, both mono- and di-fluorinated TCNQ derivatives show two well-resolved, diffusion-controlled chemically and electrochemically reversible one-electron-transfer processes under the conditions of cyclic voltammetry. The reversible potentials of the mono- and difluoro-TCNQ were determined for both the monoanionic and dianionic processes, that is, TCNQF0/1−/2− and TCNQF2 0/1−/2−. A Hammett plot shows a linear relationship of the potential differences between the three fluorinated derivatives and TCNQ with the sum of the Hammett constants for fluoro substitution. A significant positive shift in the reversible potential is found by increasing the number of fluoro substituents. Although the first TCNQFn 0/1− (n=1,2) reduction process is not affected by addition of trifluoroacetic acid (TFA), the dianions are more basic and rapidly protonate to form H2TCNQFn. This explains the significant change detected in the electrochemistry of the second TCNQFn 1−/2− redox process. The addition of TFA to solutions of the monoanionic form also gives rise to the disproportionation of TCNQFn 1− to TCNQFn and H2TCNQFn, as proven electrochemically and spectroscopically. Furthermore, a higher number of fluoro substituents results in the reduced form of the molecule being more stable, as evidenced by both UV/Vis spectra and voltammetric measurements. Finally, we performed DFT calculations for TCNQF2 and TCNQF2 to produce a spectroscopic library of characteristic IR and Raman bands for these species. These data are used for comparisons with earlier calculations for TCNQF4, and we report the experimental and calculated infrared and Raman spectra for TCNQF and TCNQF2. The vibrational frequencies of the trifluorinated species, TCNQF3, were also calculated to complete the series.

AB - The electrochemistry and acid-base chemistry of TCNQF and TCNQF2 (TCNQ=7,7,8,8-tetracyanoquinodimethane) are described, and the results are compared to those reported previously for TCNQ and TCNQF4. In acetonitrile solution, both mono- and di-fluorinated TCNQ derivatives show two well-resolved, diffusion-controlled chemically and electrochemically reversible one-electron-transfer processes under the conditions of cyclic voltammetry. The reversible potentials of the mono- and difluoro-TCNQ were determined for both the monoanionic and dianionic processes, that is, TCNQF0/1−/2− and TCNQF2 0/1−/2−. A Hammett plot shows a linear relationship of the potential differences between the three fluorinated derivatives and TCNQ with the sum of the Hammett constants for fluoro substitution. A significant positive shift in the reversible potential is found by increasing the number of fluoro substituents. Although the first TCNQFn 0/1− (n=1,2) reduction process is not affected by addition of trifluoroacetic acid (TFA), the dianions are more basic and rapidly protonate to form H2TCNQFn. This explains the significant change detected in the electrochemistry of the second TCNQFn 1−/2− redox process. The addition of TFA to solutions of the monoanionic form also gives rise to the disproportionation of TCNQFn 1− to TCNQFn and H2TCNQFn, as proven electrochemically and spectroscopically. Furthermore, a higher number of fluoro substituents results in the reduced form of the molecule being more stable, as evidenced by both UV/Vis spectra and voltammetric measurements. Finally, we performed DFT calculations for TCNQF2 and TCNQF2 to produce a spectroscopic library of characteristic IR and Raman bands for these species. These data are used for comparisons with earlier calculations for TCNQF4, and we report the experimental and calculated infrared and Raman spectra for TCNQF and TCNQF2. The vibrational frequencies of the trifluorinated species, TCNQF3, were also calculated to complete the series.

KW - acid-base chemistry

KW - density functional theory

KW - electrochemistry

KW - fluorinated-TCNQ

KW - vibrational spectroscopy

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U2 - 10.1002/celc.201701387

DO - 10.1002/celc.201701387

M3 - Article

VL - 5

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EP - 1185

JO - ChemElectroChem

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SN - 2196-0216

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