Research Article

Eliminating nonradiative decay in Cu(I) emitters: >99% quantum efficiency and microsecond lifetime

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Science  08 Feb 2019:
Vol. 363, Issue 6427, pp. 601-606
DOI: 10.1126/science.aav2865

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Helping copper glow

Copper's abundance makes the metal an appealing candidate for luminescence applications. However, many copper complexes tend to decay nonradiatively after photoexcitation. A recently described exception involves a two-coordinate complex that sandwiches the metal between an amide ligand and a carbene ligand. Hamze et al. thoroughly explored this motif and measured a nearly perfect luminescence efficiency. They used this property to produce a prototype blue organic light-emitting diode. The photodynamics appeared largely ligand-centered, with the excited state attributed to copper-facilitated charge transfer from amide to carbene.

Science, this issue p. 601

Abstract

Luminescent complexes of heavy metals such as iridium, platinum, and ruthenium play an important role in photocatalysis and energy conversion applications as well as organic light-emitting diodes (OLEDs). Achieving comparable performance from more–earth-abundant copper requires overcoming the weak spin-orbit coupling of the light metal as well as limiting the high reorganization energies typical in copper(I) [Cu(I)] complexes. Here we report that two-coordinate Cu(I) complexes with redox active ligands in coplanar conformation manifest suppressed nonradiative decay, reduced structural reorganization, and sufficient orbital overlap for efficient charge transfer. We achieve photoluminescence efficiencies >99% and microsecond lifetimes, which lead to an efficient blue-emitting OLED. Photophysical analysis and simulations reveal a temperature-dependent interplay between emissive singlet and triplet charge-transfer states and amide-localized triplet states.

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