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Spectroscopic and theoretical investigation of color tuning in deep-red luminescent iridium(III) complexes

Spectroscopic and theoretical investigation of color tuning in deep-red luminescent iridium(III) complexes
Spectroscopic and theoretical investigation of color tuning in deep-red luminescent iridium(III) complexes
A series of heteroleptic, neutral iridium(III) complexes of the form [Ir(L)2(N^O)] (where L = cyclometalated 2,3-disubstituted quinoxaline and N^O = ancillary picolinate or pyrazinoate) are described in terms of their synthesis and spectroscopic properties, with supporting computational analyses providing additional insight into the electronic properties. The 10 [Ir(L)2(N^O)] complexes were characterized using a range of analytical techniques (including 1H, 13C, and 19F NMR and IR spectroscopies and mass spectrometry). One of the examples was structurally characterized using X-ray diffraction. The redox properties were determined using cyclic voltammetry, and the electronic properties were investigated using UV–vis, time-resolved luminescence, and transient absorption spectroscopies. The complexes are phosphorescent in the red region of the visible spectrum (λem = 633–680 nm), with lifetimes typically of hundreds of nanoseconds and quantum yields ca. 5% in aerated chloroform. A combination of spectroscopic and computational analyses suggests that the long-wavelength absorption and emission properties of these complexes are strongly characterized by a combination of spin-forbidden metal-to-ligand charge-transfer and quinoxaline-centered transitions. The emission wavelength in these complexes can thus be controlled in two ways: first, substitution of the cyclometalating quinoxaline ligand can perturb both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital levels (LUMO, Cl atoms on the ligand induce the largest bathochromic shift), and second, the choice of the ancillary ligand can influence the HOMO energy (pyrazinoate stabilizes the HOMO, inducing hypsochromic shifts).
0020-1669
2266-2277
Stonelake, Thomas M.
c72d5105-aa44-48fe-9641-5d43aa810eb0
Philips, Kaitlin A.
f7621f13-8f58-42d3-a232-b098e2106f13
Otaif, Haleema Y.
1b365536-1683-40d5-b6d2-3f869cdac579
Edwardson, Zachary C.
428d6f86-419c-4673-b41b-8ed496b1dbe0
Horton, Peter
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Beames, Joseph M.
73b04545-4859-44ad-999e-551f82924c29
Pope, Simon J.A.
db9a489c-29ba-41cd-a96a-623bace0889d
Stonelake, Thomas M.
c72d5105-aa44-48fe-9641-5d43aa810eb0
Philips, Kaitlin A.
f7621f13-8f58-42d3-a232-b098e2106f13
Otaif, Haleema Y.
1b365536-1683-40d5-b6d2-3f869cdac579
Edwardson, Zachary C.
428d6f86-419c-4673-b41b-8ed496b1dbe0
Horton, Peter
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Beames, Joseph M.
73b04545-4859-44ad-999e-551f82924c29
Pope, Simon J.A.
db9a489c-29ba-41cd-a96a-623bace0889d

Stonelake, Thomas M., Philips, Kaitlin A., Otaif, Haleema Y., Edwardson, Zachary C., Horton, Peter, Coles, Simon J., Beames, Joseph M. and Pope, Simon J.A. (2020) Spectroscopic and theoretical investigation of color tuning in deep-red luminescent iridium(III) complexes. Inorganic Chemistry, 59 (4), 2266-2277. (doi:10.1021/acs.inorgchem.9b02991).

Record type: Article

Abstract

A series of heteroleptic, neutral iridium(III) complexes of the form [Ir(L)2(N^O)] (where L = cyclometalated 2,3-disubstituted quinoxaline and N^O = ancillary picolinate or pyrazinoate) are described in terms of their synthesis and spectroscopic properties, with supporting computational analyses providing additional insight into the electronic properties. The 10 [Ir(L)2(N^O)] complexes were characterized using a range of analytical techniques (including 1H, 13C, and 19F NMR and IR spectroscopies and mass spectrometry). One of the examples was structurally characterized using X-ray diffraction. The redox properties were determined using cyclic voltammetry, and the electronic properties were investigated using UV–vis, time-resolved luminescence, and transient absorption spectroscopies. The complexes are phosphorescent in the red region of the visible spectrum (λem = 633–680 nm), with lifetimes typically of hundreds of nanoseconds and quantum yields ca. 5% in aerated chloroform. A combination of spectroscopic and computational analyses suggests that the long-wavelength absorption and emission properties of these complexes are strongly characterized by a combination of spin-forbidden metal-to-ligand charge-transfer and quinoxaline-centered transitions. The emission wavelength in these complexes can thus be controlled in two ways: first, substitution of the cyclometalating quinoxaline ligand can perturb both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital levels (LUMO, Cl atoms on the ligand induce the largest bathochromic shift), and second, the choice of the ancillary ligand can influence the HOMO energy (pyrazinoate stabilizes the HOMO, inducing hypsochromic shifts).

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Accepted/In Press date: 20 January 2020
e-pub ahead of print date: 4 February 2020

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Local EPrints ID: 437988
URI: http://eprints.soton.ac.uk/id/eprint/437988
ISSN: 0020-1669
PURE UUID: f823bebf-7048-4ab9-b235-d1430b47d785
ORCID for Peter Horton: ORCID iD orcid.org/0000-0001-8886-2016
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272

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Date deposited: 25 Feb 2020 17:31
Last modified: 19 May 2020 00:31

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