Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole

Sergey I. Druzhinin, Sergey A. Kovalenko, Tamara A. Senyushkina, A. Demeter, Regis Januskevicius, Peter Mayer, Dietmar Stalke, Reinhard Machinek, Klaas A. Zachariasse

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Abstract

With 4-fluorofluorazene (FPP4F) and its flexible counterpart 4-fTuoro-N-phenylpyrrole (PP4F) an intramolecular charge transfer (ICT) reaction occurs in the singlet excited state in sufficiently polar solvents. The ICT reaction begins to appear in tetrahydrofuran (ξ= 7.4) for FPP4F and in the more polar 1,2-dichloroethane (ξ = 10.4) with PP4F, showing its presence by dual fluorescence from a locally excited (LE) and an ICT state. Only LE fluorescence is observed in less polar solvents such as n-hexane. The ICT reaction is more pronounced with FPP4F than for PP4F, due to the smaller energy gap ΔE(S 1,S 2) of the former molecule, in accordance with the PICT model. The occurrence of an ICT reaction is confirmed by the ICT dipóle moments μ e(ICT) of 12 D (FPP4F) and 10 D (PP4F), clearly larger than μ 6(LE) of ∼4 D for FPP4F and PP4F. Isoemissive points are found in the fluorescence spectra of FPP4F and PP4F in acetonitrile (MeCN), ethyl cyanide (EtCN), and n-propyl cyanide (PrCN) as a function of temperature, confirming the two-state (LE and ICT) reaction mechanism. From plots of the logarithm of the ICT/LE fluorescence quantum yield ratio versus the reciprocal absolute temperature in these solvents, the ICT reaction enthalpies AH are determined, with larger -AH values for FPP4F than for PP4F: 19.2 as compared with 14.9 kJ/mol in MeCN, as an example. The picosecond fluorescence decay of PP4F at -45 °C becomes slower with decreasing solvent polarity, 5.1 ps (MeCN), 14 ps (EtCN), and 35 ps (PrCN), from which the LE → ICT reaction rate constant is calculated, decreasing from 19 x 10 10 to 2.1 x 10 10 s -1 between MeCN and PrCN. The femtosecond LE excited-state absorption spectra of FPP4F and PP4F do not undergo any time development in n-hexane (no ICT reaction), but show a fast ICT reaction in MeCN at 22 °C, with decay times of 1.1 ps (FPP4F) and 3.3 ps (PP4F). It is concluded that FPP4F and PP4F have a planar ICT state (PICT model), indicating that a perpendicular twist of the donor and acceptor subgroups in a donor/acceptor molecule is not a requirement for fast and efficient ICT. The molecular structures of FPP4F and PP4F obtained from X-ray crystal analysis reveal that the pyrrole group of PP4F is twisted over an angle θ = 25° relative to the fluorophenyl moiety in the ground state, whereas as expected FPP4F is practically planar (θ = 2°). The pyrrole-phenyl bond length of FPP4F (140.7 pm) is shorter than that for PP4F (141.8 pm).

Original languageEnglish
Pages (from-to)9304-9320
Number of pages17
JournalJournal of Physical Chemistry A
Volume113
Issue number33
DOIs
Publication statusPublished - 2009

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Charge transfer
charge transfer
cyanides
Fluorescence
Cyanides
fluorescence
Excited states
Pyrroles
4-fluoro-N-phenylpyrrole
4-fluorofluorazene
pyrroles
excitation
Molecules
Bond length
decay
Quantum yield
subgroups
tetrahydrofuran
logarithms
Ground state

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Druzhinin, S. I., Kovalenko, S. A., Senyushkina, T. A., Demeter, A., Januskevicius, R., Mayer, P., ... Zachariasse, K. A. (2009). Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole. Journal of Physical Chemistry A, 113(33), 9304-9320. https://doi.org/10.1021/jp903613c

Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole. / Druzhinin, Sergey I.; Kovalenko, Sergey A.; Senyushkina, Tamara A.; Demeter, A.; Januskevicius, Regis; Mayer, Peter; Stalke, Dietmar; Machinek, Reinhard; Zachariasse, Klaas A.

In: Journal of Physical Chemistry A, Vol. 113, No. 33, 2009, p. 9304-9320.

Research output: Contribution to journalArticle

Druzhinin, SI, Kovalenko, SA, Senyushkina, TA, Demeter, A, Januskevicius, R, Mayer, P, Stalke, D, Machinek, R & Zachariasse, KA 2009, 'Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole', Journal of Physical Chemistry A, vol. 113, no. 33, pp. 9304-9320. https://doi.org/10.1021/jp903613c
Druzhinin, Sergey I. ; Kovalenko, Sergey A. ; Senyushkina, Tamara A. ; Demeter, A. ; Januskevicius, Regis ; Mayer, Peter ; Stalke, Dietmar ; Machinek, Reinhard ; Zachariasse, Klaas A. / Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole. In: Journal of Physical Chemistry A. 2009 ; Vol. 113, No. 33. pp. 9304-9320.
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abstract = "With 4-fluorofluorazene (FPP4F) and its flexible counterpart 4-fTuoro-N-phenylpyrrole (PP4F) an intramolecular charge transfer (ICT) reaction occurs in the singlet excited state in sufficiently polar solvents. The ICT reaction begins to appear in tetrahydrofuran (ξ= 7.4) for FPP4F and in the more polar 1,2-dichloroethane (ξ = 10.4) with PP4F, showing its presence by dual fluorescence from a locally excited (LE) and an ICT state. Only LE fluorescence is observed in less polar solvents such as n-hexane. The ICT reaction is more pronounced with FPP4F than for PP4F, due to the smaller energy gap ΔE(S 1,S 2) of the former molecule, in accordance with the PICT model. The occurrence of an ICT reaction is confirmed by the ICT dip{\'o}le moments μ e(ICT) of 12 D (FPP4F) and 10 D (PP4F), clearly larger than μ 6(LE) of ∼4 D for FPP4F and PP4F. Isoemissive points are found in the fluorescence spectra of FPP4F and PP4F in acetonitrile (MeCN), ethyl cyanide (EtCN), and n-propyl cyanide (PrCN) as a function of temperature, confirming the two-state (LE and ICT) reaction mechanism. From plots of the logarithm of the ICT/LE fluorescence quantum yield ratio versus the reciprocal absolute temperature in these solvents, the ICT reaction enthalpies AH are determined, with larger -AH values for FPP4F than for PP4F: 19.2 as compared with 14.9 kJ/mol in MeCN, as an example. The picosecond fluorescence decay of PP4F at -45 °C becomes slower with decreasing solvent polarity, 5.1 ps (MeCN), 14 ps (EtCN), and 35 ps (PrCN), from which the LE → ICT reaction rate constant is calculated, decreasing from 19 x 10 10 to 2.1 x 10 10 s -1 between MeCN and PrCN. The femtosecond LE excited-state absorption spectra of FPP4F and PP4F do not undergo any time development in n-hexane (no ICT reaction), but show a fast ICT reaction in MeCN at 22 °C, with decay times of 1.1 ps (FPP4F) and 3.3 ps (PP4F). It is concluded that FPP4F and PP4F have a planar ICT state (PICT model), indicating that a perpendicular twist of the donor and acceptor subgroups in a donor/acceptor molecule is not a requirement for fast and efficient ICT. The molecular structures of FPP4F and PP4F obtained from X-ray crystal analysis reveal that the pyrrole group of PP4F is twisted over an angle θ = 25° relative to the fluorophenyl moiety in the ground state, whereas as expected FPP4F is practically planar (θ = 2°). The pyrrole-phenyl bond length of FPP4F (140.7 pm) is shorter than that for PP4F (141.8 pm).",
author = "Druzhinin, {Sergey I.} and Kovalenko, {Sergey A.} and Senyushkina, {Tamara A.} and A. Demeter and Regis Januskevicius and Peter Mayer and Dietmar Stalke and Reinhard Machinek and Zachariasse, {Klaas A.}",
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TY - JOUR

T1 - Intramolecular charge transfer with 4-fluorofluorazene and the flexible 4-fluoro-N-phenylpyrrole

AU - Druzhinin, Sergey I.

AU - Kovalenko, Sergey A.

AU - Senyushkina, Tamara A.

AU - Demeter, A.

AU - Januskevicius, Regis

AU - Mayer, Peter

AU - Stalke, Dietmar

AU - Machinek, Reinhard

AU - Zachariasse, Klaas A.

PY - 2009

Y1 - 2009

N2 - With 4-fluorofluorazene (FPP4F) and its flexible counterpart 4-fTuoro-N-phenylpyrrole (PP4F) an intramolecular charge transfer (ICT) reaction occurs in the singlet excited state in sufficiently polar solvents. The ICT reaction begins to appear in tetrahydrofuran (ξ= 7.4) for FPP4F and in the more polar 1,2-dichloroethane (ξ = 10.4) with PP4F, showing its presence by dual fluorescence from a locally excited (LE) and an ICT state. Only LE fluorescence is observed in less polar solvents such as n-hexane. The ICT reaction is more pronounced with FPP4F than for PP4F, due to the smaller energy gap ΔE(S 1,S 2) of the former molecule, in accordance with the PICT model. The occurrence of an ICT reaction is confirmed by the ICT dipóle moments μ e(ICT) of 12 D (FPP4F) and 10 D (PP4F), clearly larger than μ 6(LE) of ∼4 D for FPP4F and PP4F. Isoemissive points are found in the fluorescence spectra of FPP4F and PP4F in acetonitrile (MeCN), ethyl cyanide (EtCN), and n-propyl cyanide (PrCN) as a function of temperature, confirming the two-state (LE and ICT) reaction mechanism. From plots of the logarithm of the ICT/LE fluorescence quantum yield ratio versus the reciprocal absolute temperature in these solvents, the ICT reaction enthalpies AH are determined, with larger -AH values for FPP4F than for PP4F: 19.2 as compared with 14.9 kJ/mol in MeCN, as an example. The picosecond fluorescence decay of PP4F at -45 °C becomes slower with decreasing solvent polarity, 5.1 ps (MeCN), 14 ps (EtCN), and 35 ps (PrCN), from which the LE → ICT reaction rate constant is calculated, decreasing from 19 x 10 10 to 2.1 x 10 10 s -1 between MeCN and PrCN. The femtosecond LE excited-state absorption spectra of FPP4F and PP4F do not undergo any time development in n-hexane (no ICT reaction), but show a fast ICT reaction in MeCN at 22 °C, with decay times of 1.1 ps (FPP4F) and 3.3 ps (PP4F). It is concluded that FPP4F and PP4F have a planar ICT state (PICT model), indicating that a perpendicular twist of the donor and acceptor subgroups in a donor/acceptor molecule is not a requirement for fast and efficient ICT. The molecular structures of FPP4F and PP4F obtained from X-ray crystal analysis reveal that the pyrrole group of PP4F is twisted over an angle θ = 25° relative to the fluorophenyl moiety in the ground state, whereas as expected FPP4F is practically planar (θ = 2°). The pyrrole-phenyl bond length of FPP4F (140.7 pm) is shorter than that for PP4F (141.8 pm).

AB - With 4-fluorofluorazene (FPP4F) and its flexible counterpart 4-fTuoro-N-phenylpyrrole (PP4F) an intramolecular charge transfer (ICT) reaction occurs in the singlet excited state in sufficiently polar solvents. The ICT reaction begins to appear in tetrahydrofuran (ξ= 7.4) for FPP4F and in the more polar 1,2-dichloroethane (ξ = 10.4) with PP4F, showing its presence by dual fluorescence from a locally excited (LE) and an ICT state. Only LE fluorescence is observed in less polar solvents such as n-hexane. The ICT reaction is more pronounced with FPP4F than for PP4F, due to the smaller energy gap ΔE(S 1,S 2) of the former molecule, in accordance with the PICT model. The occurrence of an ICT reaction is confirmed by the ICT dipóle moments μ e(ICT) of 12 D (FPP4F) and 10 D (PP4F), clearly larger than μ 6(LE) of ∼4 D for FPP4F and PP4F. Isoemissive points are found in the fluorescence spectra of FPP4F and PP4F in acetonitrile (MeCN), ethyl cyanide (EtCN), and n-propyl cyanide (PrCN) as a function of temperature, confirming the two-state (LE and ICT) reaction mechanism. From plots of the logarithm of the ICT/LE fluorescence quantum yield ratio versus the reciprocal absolute temperature in these solvents, the ICT reaction enthalpies AH are determined, with larger -AH values for FPP4F than for PP4F: 19.2 as compared with 14.9 kJ/mol in MeCN, as an example. The picosecond fluorescence decay of PP4F at -45 °C becomes slower with decreasing solvent polarity, 5.1 ps (MeCN), 14 ps (EtCN), and 35 ps (PrCN), from which the LE → ICT reaction rate constant is calculated, decreasing from 19 x 10 10 to 2.1 x 10 10 s -1 between MeCN and PrCN. The femtosecond LE excited-state absorption spectra of FPP4F and PP4F do not undergo any time development in n-hexane (no ICT reaction), but show a fast ICT reaction in MeCN at 22 °C, with decay times of 1.1 ps (FPP4F) and 3.3 ps (PP4F). It is concluded that FPP4F and PP4F have a planar ICT state (PICT model), indicating that a perpendicular twist of the donor and acceptor subgroups in a donor/acceptor molecule is not a requirement for fast and efficient ICT. The molecular structures of FPP4F and PP4F obtained from X-ray crystal analysis reveal that the pyrrole group of PP4F is twisted over an angle θ = 25° relative to the fluorophenyl moiety in the ground state, whereas as expected FPP4F is practically planar (θ = 2°). The pyrrole-phenyl bond length of FPP4F (140.7 pm) is shorter than that for PP4F (141.8 pm).

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