Direct observation of intersystem crossing in a thermally activated delayed fluorescence copper complex in the solid state
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Intersystem crossing in thermally activated delayed fluorescent (TADF) materials is an important process that controls the rate at which singlet states convert to triplets, measuring this directly in TADF materials is difficult. Thermally activated delayed fluorescence is a significant emerging technology that enables harvesting of triplets as well as singlet excited states for emission in organic light emitting diodes. We have observed the picosecond time-resolved photoluminescence of a highly luminescent, neutral copper(I) complex in the solid state that shows TADF. The time constant of intersystem crossing is measured to be 27 ps. Subsequent overall reverse intersystem crossing is slow, leading to population equilibration and TADF with an average lifetime of 11.5 μs. These first measurements of intersystem crossing in the solid state in this class of mononuclear copper(I) complexes give better understanding of the excited state processes and mechanisms that ensure efficient TADF.
Bergmann , L , Hedley , G J , Baumann , T , Braese , S & Samuel , I D W 2016 , ' Direct observation of intersystem crossing in a thermally activated delayed fluorescence copper complex in the solid state ' Science Advances , vol 2 , no. 1 , e1500889 . DOI: 10.1126/sciadv.1500889
Copyright © 2016, The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The authors are grateful to CYNORA GmbH for financial support. This work was supported by the Engineering and Physical Sciences Research Council (grant number EP/J009016/1) and by the European Union Seventh Framework Programme under grant agreement 321305.