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Charge resonance excitations in 1,3-bis[di(4-methoxyphenyl)aminolazulene radical cations

Nöll, Gilbert LU ; Amthor, Stephan; Avola, Manuele; Lambert, Christoph and Daub, Joerg (2007) In Journal of Physical Chemistry C 111(8). p.3512-3516
Abstract
The 1,3-bis[di(4-methoxyphenyl)amino]azulene 1 and 1,3-bis[di(4-methoxyphenyl)amino]azulene-2-carboxylic acid methyl ester 2 were synthesized and investigated by spectroscopic and electrochemical methods in order to estimate the electronic coupling between the attached amine redox centers. We found that the electronic coupling V which is mediated by a nonalternant 1,3-azulene bridge in the radical cation 2(+) (V = 3900 cm(-1)) is almost the same as in the isomeric alternant 1,4-naphthalene system 3(+) (V = 4000 cm(-1)). The electrochemical stability of azulene derivatives is drastically increased by substituents at the 2-position: whereas the oxidation of compound 1 is irreversible, the methylearboxylate derivative 2 undergoes four... (More)
The 1,3-bis[di(4-methoxyphenyl)amino]azulene 1 and 1,3-bis[di(4-methoxyphenyl)amino]azulene-2-carboxylic acid methyl ester 2 were synthesized and investigated by spectroscopic and electrochemical methods in order to estimate the electronic coupling between the attached amine redox centers. We found that the electronic coupling V which is mediated by a nonalternant 1,3-azulene bridge in the radical cation 2(+) (V = 3900 cm(-1)) is almost the same as in the isomeric alternant 1,4-naphthalene system 3(+) (V = 4000 cm(-1)). The electrochemical stability of azulene derivatives is drastically increased by substituents at the 2-position: whereas the oxidation of compound 1 is irreversible, the methylearboxylate derivative 2 undergoes four reversible oxidation processes in CH2Cl2 under semi-infinite conditions. The different redox states of the corresponding radical cations are well separated. However, under finite diffusion conditions only the first three oxidation processes are reversible. The absorption spectra of the radical cations of 2(+), 2(2+), and 2(3+) show intense absorption bands in the NIR region. The analysis of the optical spectra as well as DFT calculations indicate that in 2(+) the charge is symmetrically distributed similar to the naphthalene isomer 3(+). Thus, the 1,3-azulene unit and its derivatives are useful bridging units due to their ability to mediate a strong electronic coupling similar to naphthalene but with a less positive redox potential. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry C
volume
111
issue
8
pages
3512 - 3516
publisher
The American Chemical Society
external identifiers
  • wos:000245005900046
  • scopus:33947419744
ISSN
1932-7447
DOI
10.1021/jp066385a
language
English
LU publication?
yes
id
d9f55a56-96f9-4aa0-b73e-976562c0ef30 (old id 670089)
date added to LUP
2007-12-14 09:45:28
date last changed
2017-09-17 05:01:56
@article{d9f55a56-96f9-4aa0-b73e-976562c0ef30,
  abstract     = {The 1,3-bis[di(4-methoxyphenyl)amino]azulene 1 and 1,3-bis[di(4-methoxyphenyl)amino]azulene-2-carboxylic acid methyl ester 2 were synthesized and investigated by spectroscopic and electrochemical methods in order to estimate the electronic coupling between the attached amine redox centers. We found that the electronic coupling V which is mediated by a nonalternant 1,3-azulene bridge in the radical cation 2(+) (V = 3900 cm(-1)) is almost the same as in the isomeric alternant 1,4-naphthalene system 3(+) (V = 4000 cm(-1)). The electrochemical stability of azulene derivatives is drastically increased by substituents at the 2-position: whereas the oxidation of compound 1 is irreversible, the methylearboxylate derivative 2 undergoes four reversible oxidation processes in CH2Cl2 under semi-infinite conditions. The different redox states of the corresponding radical cations are well separated. However, under finite diffusion conditions only the first three oxidation processes are reversible. The absorption spectra of the radical cations of 2(+), 2(2+), and 2(3+) show intense absorption bands in the NIR region. The analysis of the optical spectra as well as DFT calculations indicate that in 2(+) the charge is symmetrically distributed similar to the naphthalene isomer 3(+). Thus, the 1,3-azulene unit and its derivatives are useful bridging units due to their ability to mediate a strong electronic coupling similar to naphthalene but with a less positive redox potential.},
  author       = {Nöll, Gilbert and Amthor, Stephan and Avola, Manuele and Lambert, Christoph and Daub, Joerg},
  issn         = {1932-7447},
  language     = {eng},
  number       = {8},
  pages        = {3512--3516},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry C},
  title        = {Charge resonance excitations in 1,3-bis[di(4-methoxyphenyl)aminolazulene radical cations},
  url          = {http://dx.doi.org/10.1021/jp066385a},
  volume       = {111},
  year         = {2007},
}