Electronic structure and quadratic hyperpolarizabilities in organotransition-metal chromophores having weakly coupled π-networks. Unusual mechanisms for second-order response

David R. Kanis, Pascal G. Lacroix, Mark A Ratner, Tobin J Marks

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Abstract

This contribution describes the use of the computationally efficient, chemically-oriented INDO-SOS electronic structure model (ZINDO) to elucidate the electronic origins of the second-order nonlinear optical (NLO) response in molecules with extended π-architectures weakly coupled to transition-metal fragments. ZINDO-derived quadratic hyperpolarizabilities are found to be in excellent agreement with experiment for a variety of group 6 pyridine pentacarbonyl complexes in which coordination to the low-valent metal fragments enhances the NLO response of the free ligands. The metal-pyridine chromophores are found to obey the classical two-level model. However, the β-dictating MLCT transitions possess significantly larger Δμge values and markedly lower oscillator strengths relative to the traditional organic chromophore π-donor-acceptor architectures by virtue of weak coupling between the metal and the ligand π-network. The computed quadratic hyperpolarizabilities of group 6 stilbazole pentacarbonyl derivatives are in good agreement with experiment. In contrast to conventional organic chromophores, an increase in π-conjugation length of the stilbazole ligands does not result in a dramatic increase in the second-order response or a decrease in the HOMO → LUMO transition energy. The molecular orbital analysis indicates that the metal pentacarbonyl fragment acts as σ-acceptor, forcing the adjacent pyridine ring to become the molecular LUMO. As a consequence, the seemingly innocent pyridine ring becomes a primary charge acceptor in these structures, regardless of the derivatization or conjugation length. The synthesis and characterization of the donor-functionalized chromophore (4-(dimethylamino)-4′-stilbazole)W(CO)5 is also reported. The large observed βvec value supports the proposed NLO response model.

Original languageEnglish
Pages (from-to)10089-10102
Number of pages14
JournalJournal of the American Chemical Society
Volume116
Issue number22
Publication statusPublished - Nov 2 1994

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Chromophores
Pyridine
Electronic structure
Metals
Ligands
Molecular orbitals
Carbon Monoxide
Transition metals
Experiments
Derivatives
Molecules
pyridine

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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title = "Electronic structure and quadratic hyperpolarizabilities in organotransition-metal chromophores having weakly coupled π-networks. Unusual mechanisms for second-order response",
abstract = "This contribution describes the use of the computationally efficient, chemically-oriented INDO-SOS electronic structure model (ZINDO) to elucidate the electronic origins of the second-order nonlinear optical (NLO) response in molecules with extended π-architectures weakly coupled to transition-metal fragments. ZINDO-derived quadratic hyperpolarizabilities are found to be in excellent agreement with experiment for a variety of group 6 pyridine pentacarbonyl complexes in which coordination to the low-valent metal fragments enhances the NLO response of the free ligands. The metal-pyridine chromophores are found to obey the classical two-level model. However, the β-dictating MLCT transitions possess significantly larger Δμge values and markedly lower oscillator strengths relative to the traditional organic chromophore π-donor-acceptor architectures by virtue of weak coupling between the metal and the ligand π-network. The computed quadratic hyperpolarizabilities of group 6 stilbazole pentacarbonyl derivatives are in good agreement with experiment. In contrast to conventional organic chromophores, an increase in π-conjugation length of the stilbazole ligands does not result in a dramatic increase in the second-order response or a decrease in the HOMO → LUMO transition energy. The molecular orbital analysis indicates that the metal pentacarbonyl fragment acts as σ-acceptor, forcing the adjacent pyridine ring to become the molecular LUMO. As a consequence, the seemingly innocent pyridine ring becomes a primary charge acceptor in these structures, regardless of the derivatization or conjugation length. The synthesis and characterization of the donor-functionalized chromophore (4-(dimethylamino)-4′-stilbazole)W(CO)5 is also reported. The large observed βvec value supports the proposed NLO response model.",
author = "Kanis, {David R.} and Lacroix, {Pascal G.} and Ratner, {Mark A} and Marks, {Tobin J}",
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T1 - Electronic structure and quadratic hyperpolarizabilities in organotransition-metal chromophores having weakly coupled π-networks. Unusual mechanisms for second-order response

AU - Kanis, David R.

AU - Lacroix, Pascal G.

AU - Ratner, Mark A

AU - Marks, Tobin J

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N2 - This contribution describes the use of the computationally efficient, chemically-oriented INDO-SOS electronic structure model (ZINDO) to elucidate the electronic origins of the second-order nonlinear optical (NLO) response in molecules with extended π-architectures weakly coupled to transition-metal fragments. ZINDO-derived quadratic hyperpolarizabilities are found to be in excellent agreement with experiment for a variety of group 6 pyridine pentacarbonyl complexes in which coordination to the low-valent metal fragments enhances the NLO response of the free ligands. The metal-pyridine chromophores are found to obey the classical two-level model. However, the β-dictating MLCT transitions possess significantly larger Δμge values and markedly lower oscillator strengths relative to the traditional organic chromophore π-donor-acceptor architectures by virtue of weak coupling between the metal and the ligand π-network. The computed quadratic hyperpolarizabilities of group 6 stilbazole pentacarbonyl derivatives are in good agreement with experiment. In contrast to conventional organic chromophores, an increase in π-conjugation length of the stilbazole ligands does not result in a dramatic increase in the second-order response or a decrease in the HOMO → LUMO transition energy. The molecular orbital analysis indicates that the metal pentacarbonyl fragment acts as σ-acceptor, forcing the adjacent pyridine ring to become the molecular LUMO. As a consequence, the seemingly innocent pyridine ring becomes a primary charge acceptor in these structures, regardless of the derivatization or conjugation length. The synthesis and characterization of the donor-functionalized chromophore (4-(dimethylamino)-4′-stilbazole)W(CO)5 is also reported. The large observed βvec value supports the proposed NLO response model.

AB - This contribution describes the use of the computationally efficient, chemically-oriented INDO-SOS electronic structure model (ZINDO) to elucidate the electronic origins of the second-order nonlinear optical (NLO) response in molecules with extended π-architectures weakly coupled to transition-metal fragments. ZINDO-derived quadratic hyperpolarizabilities are found to be in excellent agreement with experiment for a variety of group 6 pyridine pentacarbonyl complexes in which coordination to the low-valent metal fragments enhances the NLO response of the free ligands. The metal-pyridine chromophores are found to obey the classical two-level model. However, the β-dictating MLCT transitions possess significantly larger Δμge values and markedly lower oscillator strengths relative to the traditional organic chromophore π-donor-acceptor architectures by virtue of weak coupling between the metal and the ligand π-network. The computed quadratic hyperpolarizabilities of group 6 stilbazole pentacarbonyl derivatives are in good agreement with experiment. In contrast to conventional organic chromophores, an increase in π-conjugation length of the stilbazole ligands does not result in a dramatic increase in the second-order response or a decrease in the HOMO → LUMO transition energy. The molecular orbital analysis indicates that the metal pentacarbonyl fragment acts as σ-acceptor, forcing the adjacent pyridine ring to become the molecular LUMO. As a consequence, the seemingly innocent pyridine ring becomes a primary charge acceptor in these structures, regardless of the derivatization or conjugation length. The synthesis and characterization of the donor-functionalized chromophore (4-(dimethylamino)-4′-stilbazole)W(CO)5 is also reported. The large observed βvec value supports the proposed NLO response model.

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