Cross-conjugation vs. linear conjugation in donor–bridge–acceptor nitrophenol chromophores

Mikkel Andreas Christensen; Eduardo Antonio Della Pia; Jørgen Houmøller; Sean Douglas Thomsen; Marius Wanko; Andrew Bond; Angel Rubio; Steen Brøndsted Nielsen; Mogens Brøndsted Nielsen

doi:10.1002/ejoc.201301642

Cross-conjugation vs. linear conjugation in donor–bridge–acceptor nitrophenol chromophores

Mikkel Andreas Christensen, Eduardo Antonio Della Pia, Jørgen Houmøller, Sean Douglas Thomsen, Marius Wanko, Andrew Bond, Angel Rubio, Steen Brøndsted Nielsen, Mogens Brøndsted Nielsen

Department of Chemistry

6 Citations (Scopus)

Abstract

The influence of cross-conjugation vs. linear conjugation on the electronic communication between donor and acceptor groups in phenol(ate)-bridge- nitrobenzene chromophores was investigated by solution and gas-phase absorption spectroscopy, fluorescence spectroscopy, and quantum chemical calculations. The compounds studied include, among others, geminally and trans-substituted diethynylethenes prepared by stepwise Sonogashira cross-coupling reactions, and the cross-conjugated analogue of stilbene. A butadiyne-bridged donor-acceptor chromophore was prepared by an unsymmetrical Pd-catalysed coupling between a chloroalkyne and a terminal alkyne. While the linearly conjugated chromophores showed a strong and redshifted charge-transfer (CT) absorption maximum upon deprotonation in solution, a new redshifted absorption was either absent or present as a weak shoulder for the cross-conjugated derivatives. Calculations on the nonplanar 1,1-diaryl-substituted ethylene derivative revealed that the S₀-S₁ absorption has a very low oscillator strength due to insignificant coupling between the donor and acceptor ends. The energy of this CT absorption for a nonsolvated molecule is smaller than that of the linearly conjugated stilbene analogue by 0.4 eV. This result cannot directly be inferred from the solution studies. A gas-phase absorption spectrum of this chromophore was measured by action spectroscopy, which only revealed a higher-energy absorption band. Based on calculations, this band was assigned to a higher-lying π-π* transition. For the planar diethynylethene chromophores, cross-conjugation leads to a decrease of 0.3 eV in the excitation energy, according to the calculations. Finally, in contrast to the linearly conjugated chromophores, the cross-conjugated ones did not show any fluorescence, which may be due to deexcitation via the low-lying CT "dark" state.

Original language	English
Journal	European Journal of Organic Chemistry
Volume	2014
Issue number	10
Pages (from-to)	2044-2052
Number of pages	9
ISSN	1434-193X
DOIs	https://doi.org/10.1002/ejoc.201301642
Publication status	Published - Apr 2014

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title = "Cross-conjugation vs. linear conjugation in donor–bridge–acceptor nitrophenol chromophores",

abstract = "The influence of cross-conjugation vs. linear conjugation on the electronic communication between donor and acceptor groups in phenol(ate)-bridge- nitrobenzene chromophores was investigated by solution and gas-phase absorption spectroscopy, fluorescence spectroscopy, and quantum chemical calculations. The compounds studied include, among others, geminally and trans-substituted diethynylethenes prepared by stepwise Sonogashira cross-coupling reactions, and the cross-conjugated analogue of stilbene. A butadiyne-bridged donor-acceptor chromophore was prepared by an unsymmetrical Pd-catalysed coupling between a chloroalkyne and a terminal alkyne. While the linearly conjugated chromophores showed a strong and redshifted charge-transfer (CT) absorption maximum upon deprotonation in solution, a new redshifted absorption was either absent or present as a weak shoulder for the cross-conjugated derivatives. Calculations on the nonplanar 1,1-diaryl-substituted ethylene derivative revealed that the S0-S1 absorption has a very low oscillator strength due to insignificant coupling between the donor and acceptor ends. The energy of this CT absorption for a nonsolvated molecule is smaller than that of the linearly conjugated stilbene analogue by 0.4 eV. This result cannot directly be inferred from the solution studies. A gas-phase absorption spectrum of this chromophore was measured by action spectroscopy, which only revealed a higher-energy absorption band. Based on calculations, this band was assigned to a higher-lying π-π* transition. For the planar diethynylethene chromophores, cross-conjugation leads to a decrease of 0.3 eV in the excitation energy, according to the calculations. Finally, in contrast to the linearly conjugated chromophores, the cross-conjugated ones did not show any fluorescence, which may be due to deexcitation via the low-lying CT {"}dark{"} state.",

author = "Christensen, {Mikkel Andreas} and {Della Pia}, {Eduardo Antonio} and J{\o}rgen Houm{\o}ller and Thomsen, {Sean Douglas} and Marius Wanko and Andrew Bond and Angel Rubio and Nielsen, {Steen Br{\o}ndsted} and Nielsen, {Mogens Br{\o}ndsted}",

year = "2014",

month = apr,

doi = "10.1002/ejoc.201301642",

language = "English",

volume = "2014",

pages = "2044--2052",

journal = "European Journal of Organic Chemistry",

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TY - JOUR

T1 - Cross-conjugation vs. linear conjugation in donor–bridge–acceptor nitrophenol chromophores

AU - Christensen, Mikkel Andreas

AU - Della Pia, Eduardo Antonio

AU - Houmøller, Jørgen

AU - Thomsen, Sean Douglas

AU - Wanko, Marius

AU - Bond, Andrew

AU - Rubio, Angel

AU - Nielsen, Steen Brøndsted

AU - Nielsen, Mogens Brøndsted

PY - 2014/4

Y1 - 2014/4

N2 - The influence of cross-conjugation vs. linear conjugation on the electronic communication between donor and acceptor groups in phenol(ate)-bridge- nitrobenzene chromophores was investigated by solution and gas-phase absorption spectroscopy, fluorescence spectroscopy, and quantum chemical calculations. The compounds studied include, among others, geminally and trans-substituted diethynylethenes prepared by stepwise Sonogashira cross-coupling reactions, and the cross-conjugated analogue of stilbene. A butadiyne-bridged donor-acceptor chromophore was prepared by an unsymmetrical Pd-catalysed coupling between a chloroalkyne and a terminal alkyne. While the linearly conjugated chromophores showed a strong and redshifted charge-transfer (CT) absorption maximum upon deprotonation in solution, a new redshifted absorption was either absent or present as a weak shoulder for the cross-conjugated derivatives. Calculations on the nonplanar 1,1-diaryl-substituted ethylene derivative revealed that the S0-S1 absorption has a very low oscillator strength due to insignificant coupling between the donor and acceptor ends. The energy of this CT absorption for a nonsolvated molecule is smaller than that of the linearly conjugated stilbene analogue by 0.4 eV. This result cannot directly be inferred from the solution studies. A gas-phase absorption spectrum of this chromophore was measured by action spectroscopy, which only revealed a higher-energy absorption band. Based on calculations, this band was assigned to a higher-lying π-π* transition. For the planar diethynylethene chromophores, cross-conjugation leads to a decrease of 0.3 eV in the excitation energy, according to the calculations. Finally, in contrast to the linearly conjugated chromophores, the cross-conjugated ones did not show any fluorescence, which may be due to deexcitation via the low-lying CT "dark" state.

AB - The influence of cross-conjugation vs. linear conjugation on the electronic communication between donor and acceptor groups in phenol(ate)-bridge- nitrobenzene chromophores was investigated by solution and gas-phase absorption spectroscopy, fluorescence spectroscopy, and quantum chemical calculations. The compounds studied include, among others, geminally and trans-substituted diethynylethenes prepared by stepwise Sonogashira cross-coupling reactions, and the cross-conjugated analogue of stilbene. A butadiyne-bridged donor-acceptor chromophore was prepared by an unsymmetrical Pd-catalysed coupling between a chloroalkyne and a terminal alkyne. While the linearly conjugated chromophores showed a strong and redshifted charge-transfer (CT) absorption maximum upon deprotonation in solution, a new redshifted absorption was either absent or present as a weak shoulder for the cross-conjugated derivatives. Calculations on the nonplanar 1,1-diaryl-substituted ethylene derivative revealed that the S0-S1 absorption has a very low oscillator strength due to insignificant coupling between the donor and acceptor ends. The energy of this CT absorption for a nonsolvated molecule is smaller than that of the linearly conjugated stilbene analogue by 0.4 eV. This result cannot directly be inferred from the solution studies. A gas-phase absorption spectrum of this chromophore was measured by action spectroscopy, which only revealed a higher-energy absorption band. Based on calculations, this band was assigned to a higher-lying π-π* transition. For the planar diethynylethene chromophores, cross-conjugation leads to a decrease of 0.3 eV in the excitation energy, according to the calculations. Finally, in contrast to the linearly conjugated chromophores, the cross-conjugated ones did not show any fluorescence, which may be due to deexcitation via the low-lying CT "dark" state.

U2 - 10.1002/ejoc.201301642

DO - 10.1002/ejoc.201301642

M3 - Journal article

SN - 1434-193X

VL - 2014

SP - 2044

EP - 2052

JO - European Journal of Organic Chemistry

JF - European Journal of Organic Chemistry

IS - 10

ER -

Cross-conjugation vs. linear conjugation in donor–bridge–acceptor nitrophenol chromophores

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