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Durham University

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Publication details for Prof. J.A. Gareth Williams

Walden, Melissa T., Pander, Piotr, Yufit, Dmitry S., Dias, Fernando B. & Williams, J. A. Gareth (2019). Homoleptic platinum(ii) complexes with pyridyltriazole ligands: excimer-forming phosphorescent emitters for solution-processed OLEDs. Journal of Materials Chemistry C 7(22): 6592-6606.

Author(s) from Durham

Abstract

Two new homoleptic platinum(II) complexes are reported that feature aryl-appended 5-(2-pyridyl)-1,2,4-
triazole chelates acting as N^N ligating ions, PtL1
2 and PtL2
2. Readily prepared from easily accessible
proligands, they offer good solubility in organic solvents, allowing them to be incorporated into OLEDs
through solution processing. Crystal structures reveal staggered, face-to-face packing of the p systems
in adjacent complexes, but with no close PtPt interactions. The complexes display bright unimolecular
phosphorescence: for PtL1
2 and PtL2
2 respectively, lmax = 502 and 514 nm; F = 0.21 and 0.48; t = 5.1
and 4.6 ms in deoxygenated CH2Cl2 at 295 K. Both complexes show a strong propensity to form
intensely emissive excimers at higher concentrations: lmax = 585 and 625 nm for PtL1
2 and PtL2
2. The
photophysical properties in doped and neat thin films have been investigated using steady-state and
time-resolved methods. These studies highlight the presence of different environments of bimolecular
excited states with different lifetimes, those emitting at lowest energy apparently having the longest
lifetimes, contrary to what is normally found for unimolecular emitters through the effects of vibrational
deactivation. The prototype solution-processed OLEDs gave EQEs of 9.6–12.5% for PtL1
2 and 8.8–11.4%
for PtL2
2, impressive values for solution-processed devices incorporating such simple complexes and
only a little inferior to the EQE of 15% achieved using PtL1
2 in a device prepared by evaporation.
Compounds of this type have potential to provide the red and green components for white light OLEDs,
due to their tunable, uni- and bimolecular excited state emission.