Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands

Jian Li, Peter I. Djurovich, Bert D. Alleyne, Muhammed Yousufuddin, Nam N. Ho, J. Christopher Thomas, Jonas C. Peters, Robert Bau, Mark E. Thompson

Research output: Contribution to journalArticle

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Abstract

The synthesis and photophysical characterization of a series of (N,C 2′-(2-para-tolylpyridyl))2Ir(LL′) [(tpy) 2Ir(LL′)] (LL′ = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy) 2Ir(LL′)] (dfppy = N,C2′-2-(4′,6′- difluorophenyl)-pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2Ir(CN)2 - and (ppy)2Ir(NCS)2 - (ppy = N,C2′- 2-phenylpyridyl). The (tpy)2Ir(PPh2CH2) 2BPh2 and [(tpy)2Ir(CN-t-Bu) 2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-Caryl bond lengths in (tpy)2Ir(CN-t-Bu)2 + (2.047-(5) and 2.072(5) Å) and (tpy)2Ir(PPh2CH2) 2BPh2 (2.047(9) and 2.057(9) Å) are longer than their counterparts in (tpy)2Ir(acac) (1.982(6) and 1.985(7) Å). Density functional theory calculations carried out on (ppy)2Ir(CN- Me)2 + show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-π orbitals. Electrochemical analysis of the (tpy)2Ir(LL′) complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL′ ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in In(Knr) (knr = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (kr). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (kr) or extinction coefficient (ε) on (1/ΔE)2 has been demonstrated, where ΔE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm-1 for the spin-orbital coupling matrix element 〈3LC|HSO|1MLCT〉 of the (tpy) 2Ir(LL′) complexes can be deduced from this linear relationship. The (fppy)2Ir(LL′) complexes with corresponding ancillary ligands display similar trends in excited-state properties.

Original languageEnglish (US)
Pages (from-to)1713-1727
Number of pages15
JournalInorganic Chemistry
Volume44
Issue number6
DOIs
StatePublished - Mar 21 2005
Externally publishedYes

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Excited states
Ligands
ligands
excitation
Molecular orbitals
chelates
decay rates
molecular orbitals
energy
orbitals
extinction
Borates
Spectroscopic analysis
X ray crystallography
destabilization
spectroscopic analysis
Bond length
Quantum yield
coefficients
borates

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Li, J., Djurovich, P. I., Alleyne, B. D., Yousufuddin, M., Ho, N. N., Thomas, J. C., ... Thompson, M. E. (2005). Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands. Inorganic Chemistry, 44(6), 1713-1727. https://doi.org/10.1021/ic048599h

Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands. / Li, Jian; Djurovich, Peter I.; Alleyne, Bert D.; Yousufuddin, Muhammed; Ho, Nam N.; Thomas, J. Christopher; Peters, Jonas C.; Bau, Robert; Thompson, Mark E.

In: Inorganic Chemistry, Vol. 44, No. 6, 21.03.2005, p. 1713-1727.

Research output: Contribution to journalArticle

Li, J, Djurovich, PI, Alleyne, BD, Yousufuddin, M, Ho, NN, Thomas, JC, Peters, JC, Bau, R & Thompson, ME 2005, 'Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands', Inorganic Chemistry, vol. 44, no. 6, pp. 1713-1727. https://doi.org/10.1021/ic048599h
Li, Jian ; Djurovich, Peter I. ; Alleyne, Bert D. ; Yousufuddin, Muhammed ; Ho, Nam N. ; Thomas, J. Christopher ; Peters, Jonas C. ; Bau, Robert ; Thompson, Mark E. / Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands. In: Inorganic Chemistry. 2005 ; Vol. 44, No. 6. pp. 1713-1727.
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abstract = "The synthesis and photophysical characterization of a series of (N,C 2′-(2-para-tolylpyridyl))2Ir(LL′) [(tpy) 2Ir(LL′)] (LL′ = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy) 2Ir(LL′)] (dfppy = N,C2′-2-(4′,6′- difluorophenyl)-pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2Ir(CN)2 - and (ppy)2Ir(NCS)2 - (ppy = N,C2′- 2-phenylpyridyl). The (tpy)2Ir(PPh2CH2) 2BPh2 and [(tpy)2Ir(CN-t-Bu) 2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-Caryl bond lengths in (tpy)2Ir(CN-t-Bu)2 + (2.047-(5) and 2.072(5) {\AA}) and (tpy)2Ir(PPh2CH2) 2BPh2 (2.047(9) and 2.057(9) {\AA}) are longer than their counterparts in (tpy)2Ir(acac) (1.982(6) and 1.985(7) {\AA}). Density functional theory calculations carried out on (ppy)2Ir(CN- Me)2 + show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-π orbitals. Electrochemical analysis of the (tpy)2Ir(LL′) complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL′ ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in In(Knr) (knr = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (kr). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (kr) or extinction coefficient (ε) on (1/ΔE)2 has been demonstrated, where ΔE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm-1 for the spin-orbital coupling matrix element 〈3LC|HSO|1MLCT〉 of the (tpy) 2Ir(LL′) complexes can be deduced from this linear relationship. The (fppy)2Ir(LL′) complexes with corresponding ancillary ligands display similar trends in excited-state properties.",
author = "Jian Li and Djurovich, {Peter I.} and Alleyne, {Bert D.} and Muhammed Yousufuddin and Ho, {Nam N.} and Thomas, {J. Christopher} and Peters, {Jonas C.} and Robert Bau and Thompson, {Mark E.}",
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TY - JOUR

T1 - Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands

AU - Li, Jian

AU - Djurovich, Peter I.

AU - Alleyne, Bert D.

AU - Yousufuddin, Muhammed

AU - Ho, Nam N.

AU - Thomas, J. Christopher

AU - Peters, Jonas C.

AU - Bau, Robert

AU - Thompson, Mark E.

PY - 2005/3/21

Y1 - 2005/3/21

N2 - The synthesis and photophysical characterization of a series of (N,C 2′-(2-para-tolylpyridyl))2Ir(LL′) [(tpy) 2Ir(LL′)] (LL′ = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy) 2Ir(LL′)] (dfppy = N,C2′-2-(4′,6′- difluorophenyl)-pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2Ir(CN)2 - and (ppy)2Ir(NCS)2 - (ppy = N,C2′- 2-phenylpyridyl). The (tpy)2Ir(PPh2CH2) 2BPh2 and [(tpy)2Ir(CN-t-Bu) 2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-Caryl bond lengths in (tpy)2Ir(CN-t-Bu)2 + (2.047-(5) and 2.072(5) Å) and (tpy)2Ir(PPh2CH2) 2BPh2 (2.047(9) and 2.057(9) Å) are longer than their counterparts in (tpy)2Ir(acac) (1.982(6) and 1.985(7) Å). Density functional theory calculations carried out on (ppy)2Ir(CN- Me)2 + show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-π orbitals. Electrochemical analysis of the (tpy)2Ir(LL′) complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL′ ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in In(Knr) (knr = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (kr). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (kr) or extinction coefficient (ε) on (1/ΔE)2 has been demonstrated, where ΔE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm-1 for the spin-orbital coupling matrix element 〈3LC|HSO|1MLCT〉 of the (tpy) 2Ir(LL′) complexes can be deduced from this linear relationship. The (fppy)2Ir(LL′) complexes with corresponding ancillary ligands display similar trends in excited-state properties.

AB - The synthesis and photophysical characterization of a series of (N,C 2′-(2-para-tolylpyridyl))2Ir(LL′) [(tpy) 2Ir(LL′)] (LL′ = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy) 2Ir(LL′)] (dfppy = N,C2′-2-(4′,6′- difluorophenyl)-pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2Ir(CN)2 - and (ppy)2Ir(NCS)2 - (ppy = N,C2′- 2-phenylpyridyl). The (tpy)2Ir(PPh2CH2) 2BPh2 and [(tpy)2Ir(CN-t-Bu) 2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-Caryl bond lengths in (tpy)2Ir(CN-t-Bu)2 + (2.047-(5) and 2.072(5) Å) and (tpy)2Ir(PPh2CH2) 2BPh2 (2.047(9) and 2.057(9) Å) are longer than their counterparts in (tpy)2Ir(acac) (1.982(6) and 1.985(7) Å). Density functional theory calculations carried out on (ppy)2Ir(CN- Me)2 + show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-π orbitals. Electrochemical analysis of the (tpy)2Ir(LL′) complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL′ ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in In(Knr) (knr = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (kr). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (kr) or extinction coefficient (ε) on (1/ΔE)2 has been demonstrated, where ΔE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm-1 for the spin-orbital coupling matrix element 〈3LC|HSO|1MLCT〉 of the (tpy) 2Ir(LL′) complexes can be deduced from this linear relationship. The (fppy)2Ir(LL′) complexes with corresponding ancillary ligands display similar trends in excited-state properties.

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