Abstract
Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. While dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. Here, by using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we show that radical anions of 4-n-hexyl-4′-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C-N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C-N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C-N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with Kdim = 3 × 104 M-1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π-π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. The present study provides clear evidence of spatial delocalization of electrons over two molecular fragments.
| Original language | English |
|---|---|
| Pages (from-to) | 7327-7335 |
| Number of pages | 9 |
| Journal | Journal of Physical Chemistry B |
| Volume | 121 |
| Issue number | 30 |
| DOIs | |
| Publication status | Published - Aug 3 2017 |
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ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry
Cite this
Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy. / Mani, Tomoyasu; Grills, David.
In: Journal of Physical Chemistry B, Vol. 121, No. 30, 03.08.2017, p. 7327-7335.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy
AU - Mani, Tomoyasu
AU - Grills, David
PY - 2017/8/3
Y1 - 2017/8/3
N2 - Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. While dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. Here, by using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we show that radical anions of 4-n-hexyl-4′-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C-N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C-N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C-N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with Kdim = 3 × 104 M-1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π-π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. The present study provides clear evidence of spatial delocalization of electrons over two molecular fragments.
AB - Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. While dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. Here, by using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we show that radical anions of 4-n-hexyl-4′-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C-N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C-N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C-N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with Kdim = 3 × 104 M-1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π-π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. The present study provides clear evidence of spatial delocalization of electrons over two molecular fragments.
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U2 - 10.1021/acs.jpcb.7b02559
DO - 10.1021/acs.jpcb.7b02559
M3 - Article
VL - 121
SP - 7327
EP - 7335
JO - Journal of Physical Chemistry B Materials
JF - Journal of Physical Chemistry B Materials
SN - 1520-6106
IS - 30
ER -