Please use this identifier to cite or link to this item: http://hdl.handle.net/10995/111323
Title: Extended Ligand Conjugation and Dinuclearity as a Route to Efficient Platinum-based Near-infrared (NIR) Triplet Emitters and Solution-processed NIR-OLEDs
Authors: Shafikov, M. Z.
Pander, P.
Zaytsev, A. V.
Daniels, R.
Martinscroft, R.
Dias, F. B.
Williams, J. A. G.
Kozhevnikov, V. N.
Issue Date: 2021
Publisher: Royal Society of Chemistry
Royal Society of Chemistry (RSC)
Citation: Extended Ligand Conjugation and Dinuclearity as a Route to Efficient Platinum-based Near-infrared (NIR) Triplet Emitters and Solution-processed NIR-OLEDs / M. Z. Shafikov, P. Pander, A. V. Zaytsev et al. — DOI 10.1016/j.trpro.2022.01.008 // Journal of Materials Chemistry C. — 2021. — Vol. 9. — Iss. 1. — P. 127-135.
Abstract: Near infrared (NIR) emission from molecular materials is typically targeted by using more extended conjugated systems compared to visible-emitting materials. But efficiencies usually fall off due to the combined effects of increasing non-radiative and lower oscillator strengths as the energy of emissive excited states decreases. Efficient NIR-emitting organic light emitting diodes (OLEDs) are rare compared to the huge progress that has been made for visible-light devices. For organometallic emitters that contain a heavy metal ion to promote phosphorescence through the effect of enhanced spin-orbit coupling (SOC), the problem is typically exacerbated by decreased metal character in the Sn and T1 excited states as the conjugation in a bound ligand increases. Here we show how the use of a dinuclear metal complex with an extended conjugated ligand allows such effects to be mitigated compared to analogous structures with just one metal centre. The complex Pt2(bis-dthpym)(dpm)2 (complex 5) is readily prepared by a double N^C cyclometallation of 4,6-bis(dithienyl)-pyrimidine (H2bis-dthpym), with the coordination sphere of each Pt centre being completed by O^O-coordinating dipivaloylmethane (dpm). This new complex displays intense NIR emission in solution, λmax = 725 nm, with essentially no "contamination"by visible light <700 nm. The photoluminescence quantum yield of 0.17 in toluene at 300 K is vastly superior to that of the analogous mononuclear complex, where reduced SOC leads primarily to ligand-based fluorescence and only very weak phosphorescence. Computational results indicate that a key reason for the superior performance of the dinuclear system is a doubling of the number of higher-lying excited singlet states with which the T1 state may couple, to promote the formally forbidden phosphorescence process. Complex 5 has been evaluated as an NIR emitter in solution-processed OLEDs. An external quantum efficiency (EQE) of 3.6% is attained using 5 doped into TBP:PBD at 5% w/w, with a turn-on voltage of 5.6 V (at 0.01 mW cm-2). The maximum radiosity of 2.7 mW cm-2 for this device is particularly high compared to most reported NIR-emitting phosphorescent OLEDs. © The Royal Society of Chemistry.
Keywords: EXCITED STATES
HEAVY METALS
LIGANDS
LIGHT
METAL COMPLEXES
METAL IONS
ORGANIC LIGHT EMITTING DIODES (OLED)
ORGANOMETALLICS
PHOSPHORESCENCE
PLATINUM
QUANTUM EFFICIENCY
SPIN ORBIT COUPLING
DINUCLEAR METAL COMPLEX
EXCITED SINGLET STATE
EXTERNAL QUANTUM EFFICIENCY
MONONUCLEAR COMPLEXES
NEAR-INFRARED EMISSIONS
ORGANOMETALLIC EMITTERS
PHOTOLUMINESCENCE QUANTUM YIELDS
INFRARED DEVICES
URI: http://hdl.handle.net/10995/111323
Access: info:eu-repo/semantics/openAccess
SCOPUS ID: 85099183263
PURE ID: 20515831
ISSN: 2050-7534
DOI: 10.1016/j.trpro.2022.01.008
metadata.dc.description.sponsorship: We thank EPSRC for support of some parts of this work (grant ref: EP/S012788/1). M. Z. S. gratefully acknowledges financial support from the German Research Foundation (DFG), Project No. 389797483.
Appears in Collections:Научные публикации, проиндексированные в SCOPUS и WoS CC

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