Organoimido-polyoxometalate nonlinear optical chromophores: a structural, spectroscopic, and computational study

Ahmed Al-Yasari, Nick Van Steerteghem, Hayleigh Kearns, Hani El Moll, Karen Faulds, Joseph A. Wright, Bruce S. Brunschwig, Koen Clays, John Fielden

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Abstract

Ten organoimido polyoxometalate (POM)-based chromophores have been synthesized and studied by hyper-Rayleigh scattering (HRS), Stark and Resonance Raman spectroscopies, and density functional theory (DFT) calculations. HRS β0 values for chromophores with resonance electron donors are significant (up to 139 × 10-30 esu, ∼5 times greater than that of the DAS+ cation), but systems with no donor, or the -NO2 acceptor show no activity, in some cases, despite large DFT-predicted β-values. In active systems with short (phenyl) π-bridges, β0 values comfortably exceed that of the purely organic structural analogue N,N-dimethyl-4-nitroaniline (DMPNA), and intrinsic β-values, β0/N3/2 (where N is the number of bridge π-electrons) thus appear to break empirical performance limits (β0/N3/2 vs λmax) for planar organic systems. However, β0 values obtained for extended systems with a diphenylacetylene bridge are comparable to or lower than that of their nitro analogue, N,N-dimethyl-4-[(4-nitrophenyl)ethynyl]-aniline (DMNPEA). Resonance Raman spectroscopy confirms the involvement of the POM in the electronic transitions, whether donor groups are present or not, but Stark spectroscopy indicates that, in their absence, the transitions have little dipolar character (hence, NLO inactive), consistent with DFT-calculated frontier orbitals, which extend over both POM and organic group. Stark and DFT also suggest that β is enhanced in the short compounds because the extension of charge transfer (CT) onto the POM increases changes in the excited-state dipole moment. With extended π-systems, this effect does not increase CT distances, relative to a -NO2 acceptor, so β0 values do not exceed that of DMNPEA. Overall, our results show that (i) the organoimido-POM unit is an efficient acceptor for second-order NLO, but an ineffective donor; (ii) the nature of electronic transitions in arylimido-POMs is strongly influenced by the substituents of the aryl group; and (iii) organoimido-POMs outperform organic acceptors with short π-bridges, but lose their advantage with extended π-conjugation.

LanguageEnglish
Pages10181-10194
Number of pages14
JournalInorganic Chemistry
Volume56
Issue number17
Early online date15 Aug 2017
DOIs
Publication statusPublished - 5 Sep 2017

Fingerprint

Chromophores
chromophores
Density functional theory
density functional theory
Rayleigh scattering
aniline
amsonic acid
Raman spectroscopy
charge transfer
analogs
Charge transfer
Electron resonance
pi-electrons
conjugation
electronics
Dipole moment
dipole moments
Excited states
Cations
cations

Keywords

  • organoimido-polyoxometalates
  • optical materials
  • organic chromophores

Cite this

Al-Yasari, Ahmed ; Van Steerteghem, Nick ; Kearns, Hayleigh ; El Moll, Hani ; Faulds, Karen ; Wright, Joseph A. ; Brunschwig, Bruce S. ; Clays, Koen ; Fielden, John. / Organoimido-polyoxometalate nonlinear optical chromophores : a structural, spectroscopic, and computational study. In: Inorganic Chemistry. 2017 ; Vol. 56, No. 17. pp. 10181-10194.
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Al-Yasari, A, Van Steerteghem, N, Kearns, H, El Moll, H, Faulds, K, Wright, JA, Brunschwig, BS, Clays, K & Fielden, J 2017, 'Organoimido-polyoxometalate nonlinear optical chromophores: a structural, spectroscopic, and computational study' Inorganic Chemistry, vol. 56, no. 17, pp. 10181-10194. https://doi.org/10.1021/acs.inorgchem.7b00708

Organoimido-polyoxometalate nonlinear optical chromophores : a structural, spectroscopic, and computational study. / Al-Yasari, Ahmed; Van Steerteghem, Nick; Kearns, Hayleigh; El Moll, Hani; Faulds, Karen; Wright, Joseph A.; Brunschwig, Bruce S.; Clays, Koen; Fielden, John.

In: Inorganic Chemistry, Vol. 56, No. 17, 05.09.2017, p. 10181-10194.

Research output: Contribution to journalArticle

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T1 - Organoimido-polyoxometalate nonlinear optical chromophores

T2 - Inorganic Chemistry

AU - Al-Yasari, Ahmed

AU - Van Steerteghem, Nick

AU - Kearns, Hayleigh

AU - El Moll, Hani

AU - Faulds, Karen

AU - Wright, Joseph A.

AU - Brunschwig, Bruce S.

AU - Clays, Koen

AU - Fielden, John

PY - 2017/9/5

Y1 - 2017/9/5

N2 - Ten organoimido polyoxometalate (POM)-based chromophores have been synthesized and studied by hyper-Rayleigh scattering (HRS), Stark and Resonance Raman spectroscopies, and density functional theory (DFT) calculations. HRS β0 values for chromophores with resonance electron donors are significant (up to 139 × 10-30 esu, ∼5 times greater than that of the DAS+ cation), but systems with no donor, or the -NO2 acceptor show no activity, in some cases, despite large DFT-predicted β-values. In active systems with short (phenyl) π-bridges, β0 values comfortably exceed that of the purely organic structural analogue N,N-dimethyl-4-nitroaniline (DMPNA), and intrinsic β-values, β0/N3/2 (where N is the number of bridge π-electrons) thus appear to break empirical performance limits (β0/N3/2 vs λmax) for planar organic systems. However, β0 values obtained for extended systems with a diphenylacetylene bridge are comparable to or lower than that of their nitro analogue, N,N-dimethyl-4-[(4-nitrophenyl)ethynyl]-aniline (DMNPEA). Resonance Raman spectroscopy confirms the involvement of the POM in the electronic transitions, whether donor groups are present or not, but Stark spectroscopy indicates that, in their absence, the transitions have little dipolar character (hence, NLO inactive), consistent with DFT-calculated frontier orbitals, which extend over both POM and organic group. Stark and DFT also suggest that β is enhanced in the short compounds because the extension of charge transfer (CT) onto the POM increases changes in the excited-state dipole moment. With extended π-systems, this effect does not increase CT distances, relative to a -NO2 acceptor, so β0 values do not exceed that of DMNPEA. Overall, our results show that (i) the organoimido-POM unit is an efficient acceptor for second-order NLO, but an ineffective donor; (ii) the nature of electronic transitions in arylimido-POMs is strongly influenced by the substituents of the aryl group; and (iii) organoimido-POMs outperform organic acceptors with short π-bridges, but lose their advantage with extended π-conjugation.

AB - Ten organoimido polyoxometalate (POM)-based chromophores have been synthesized and studied by hyper-Rayleigh scattering (HRS), Stark and Resonance Raman spectroscopies, and density functional theory (DFT) calculations. HRS β0 values for chromophores with resonance electron donors are significant (up to 139 × 10-30 esu, ∼5 times greater than that of the DAS+ cation), but systems with no donor, or the -NO2 acceptor show no activity, in some cases, despite large DFT-predicted β-values. In active systems with short (phenyl) π-bridges, β0 values comfortably exceed that of the purely organic structural analogue N,N-dimethyl-4-nitroaniline (DMPNA), and intrinsic β-values, β0/N3/2 (where N is the number of bridge π-electrons) thus appear to break empirical performance limits (β0/N3/2 vs λmax) for planar organic systems. However, β0 values obtained for extended systems with a diphenylacetylene bridge are comparable to or lower than that of their nitro analogue, N,N-dimethyl-4-[(4-nitrophenyl)ethynyl]-aniline (DMNPEA). Resonance Raman spectroscopy confirms the involvement of the POM in the electronic transitions, whether donor groups are present or not, but Stark spectroscopy indicates that, in their absence, the transitions have little dipolar character (hence, NLO inactive), consistent with DFT-calculated frontier orbitals, which extend over both POM and organic group. Stark and DFT also suggest that β is enhanced in the short compounds because the extension of charge transfer (CT) onto the POM increases changes in the excited-state dipole moment. With extended π-systems, this effect does not increase CT distances, relative to a -NO2 acceptor, so β0 values do not exceed that of DMNPEA. Overall, our results show that (i) the organoimido-POM unit is an efficient acceptor for second-order NLO, but an ineffective donor; (ii) the nature of electronic transitions in arylimido-POMs is strongly influenced by the substituents of the aryl group; and (iii) organoimido-POMs outperform organic acceptors with short π-bridges, but lose their advantage with extended π-conjugation.

KW - organoimido-polyoxometalates

KW - optical materials

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