Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms
A series of blue-luminescent Ir(iii) complexes with a pendant binding site for lanthanide(iii) ions has been synthesized and used to prepare Ir(iii)/Ln(iii) dyads (Ln = Eu, Tb, Gd). Photophysical studies were used to establish mechanisms of Ir→Ln (Ln = Tb, Eu) energy-transfer. In the Ir/Gd dyads, wh...
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| Format: | Article |
| Language: | English |
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2014
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| Online Access: | https://repository.londonmet.ac.uk/1028/1/Dalton%20Sykes%202014.pdf |
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| author | Sykes, Daniel Cankut, Ahmet J. Ali, Noorshida Mohd Stephenson, Andrew Spall, Steven J. P. Parker, Simon C. Weinstein, Julia A. Ward, Michael D. |
| author_facet | Sykes, Daniel Cankut, Ahmet J. Ali, Noorshida Mohd Stephenson, Andrew Spall, Steven J. P. Parker, Simon C. Weinstein, Julia A. Ward, Michael D. |
| author_sort | Sykes, Daniel |
| collection | LMU |
| description | A series of blue-luminescent Ir(iii) complexes with a pendant binding site for lanthanide(iii) ions has been synthesized and used to prepare Ir(iii)/Ln(iii) dyads (Ln = Eu, Tb, Gd). Photophysical studies were used to establish mechanisms of Ir→Ln (Ln = Tb, Eu) energy-transfer. In the Ir/Gd dyads, where direct Ir→Gd energy-transfer is not possible, significant quenching of Ir-based luminescence nonetheless occurred; this can be ascribed to photoinduced electron-transfer from the photo-excited Ir unit (*Ir, 3 MLCT/3LC excited state) to the pendant pyrazolyl-pyridine site which becomes a good electron-acceptor when coordinated to an electropositive Gd(iii) centre. This electron transfer quenches the Ir-based luminescence, leading to formation of a charge-separated {Ir4+} •—(pyrazolyl-pyridine)•− state, which is short-lived possibly due to fast back electron-transfer (<20 ns). In the Ir/Tb and Ir/Eu dyads this electron-transfer pathway is again operative and leads to sensitisation of Eu-based and Tb-based emission using the energy liberated from the back electron-transfer process. In addition direct Dexter-type Ir→Ln (Ln = Tb, Eu) energy-transfer occurs on a similar timescale, meaning that there are two parallel mechanisms by which excitation energy can be transferred from *Ir to the Eu/Tb centre. Time-resolved luminescence measurements on the sensitised Eu-based emission showed both fast and slow rise-time components, associated with the PET-based and Dexter-based energy-transfer mechanisms respectively. In the Ir/Tb dyads, the Ir→Tb energy-transfer is only just thermodynamically favourable, leading to rapid Tb→Ir thermally-activated back energy-transfer and non-radiative deactivation to an extent that depends on the precise energy gap between the *Ir and Tb-based 5 D4 states. Thus, the sensitised Tb(iii)-based emission is weak and unusually short-lived due to back energy transfer, but nonetheless represents rare examples of Tb(iii) sensitisation by a energy donor that could be excited using visible light as opposed to the usually required UV excitation. |
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| format | Article |
| id | oai:repository.londonmet.ac.uk:1028 |
| institution | London Metropolitan University |
| language | English |
| last_indexed | 2024-07-09T03:46:07Z |
| publishDate | 2014 |
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| spelling | oai:repository.londonmet.ac.uk:10282020-06-22T14:37:16Z https://repository.londonmet.ac.uk/1028/ Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms Sykes, Daniel Cankut, Ahmet J. Ali, Noorshida Mohd Stephenson, Andrew Spall, Steven J. P. Parker, Simon C. Weinstein, Julia A. Ward, Michael D. 540 Chemistry & allied sciences A series of blue-luminescent Ir(iii) complexes with a pendant binding site for lanthanide(iii) ions has been synthesized and used to prepare Ir(iii)/Ln(iii) dyads (Ln = Eu, Tb, Gd). Photophysical studies were used to establish mechanisms of Ir→Ln (Ln = Tb, Eu) energy-transfer. In the Ir/Gd dyads, where direct Ir→Gd energy-transfer is not possible, significant quenching of Ir-based luminescence nonetheless occurred; this can be ascribed to photoinduced electron-transfer from the photo-excited Ir unit (*Ir, 3 MLCT/3LC excited state) to the pendant pyrazolyl-pyridine site which becomes a good electron-acceptor when coordinated to an electropositive Gd(iii) centre. This electron transfer quenches the Ir-based luminescence, leading to formation of a charge-separated {Ir4+} •—(pyrazolyl-pyridine)•− state, which is short-lived possibly due to fast back electron-transfer (<20 ns). In the Ir/Tb and Ir/Eu dyads this electron-transfer pathway is again operative and leads to sensitisation of Eu-based and Tb-based emission using the energy liberated from the back electron-transfer process. In addition direct Dexter-type Ir→Ln (Ln = Tb, Eu) energy-transfer occurs on a similar timescale, meaning that there are two parallel mechanisms by which excitation energy can be transferred from *Ir to the Eu/Tb centre. Time-resolved luminescence measurements on the sensitised Eu-based emission showed both fast and slow rise-time components, associated with the PET-based and Dexter-based energy-transfer mechanisms respectively. In the Ir/Tb dyads, the Ir→Tb energy-transfer is only just thermodynamically favourable, leading to rapid Tb→Ir thermally-activated back energy-transfer and non-radiative deactivation to an extent that depends on the precise energy gap between the *Ir and Tb-based 5 D4 states. Thus, the sensitised Tb(iii)-based emission is weak and unusually short-lived due to back energy transfer, but nonetheless represents rare examples of Tb(iii) sensitisation by a energy donor that could be excited using visible light as opposed to the usually required UV excitation. 2014-02-25 Article PeerReviewed text en https://repository.londonmet.ac.uk/1028/1/Dalton%20Sykes%202014.pdf Sykes, Daniel, Cankut, Ahmet J., Ali, Noorshida Mohd, Stephenson, Andrew, Spall, Steven J. P., Parker, Simon C., Weinstein, Julia A. and Ward, Michael D. (2014) Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms. Dalton Transactions, 43 (17). p. 6414. ISSN 1477-9226 http://dx.doi.org/10.1039/c4dt00292J 10.1039/c4dt00292J 10.1039/c4dt00292J |
| spellingShingle | 540 Chemistry & allied sciences Sykes, Daniel Cankut, Ahmet J. Ali, Noorshida Mohd Stephenson, Andrew Spall, Steven J. P. Parker, Simon C. Weinstein, Julia A. Ward, Michael D. Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title | Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title_full | Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title_fullStr | Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title_full_unstemmed | Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title_short | Sensitisation of Eu(iii)- and Tb(iii)-based luminescence by Ir(iii) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms |
| title_sort | sensitisation of eu iii and tb iii based luminescence by ir iii units in ir lanthanide dyads evidence for parallel energy transfer and electron transfer based mechanisms |
| topic | 540 Chemistry & allied sciences |
| url | https://repository.londonmet.ac.uk/1028/1/Dalton%20Sykes%202014.pdf |
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