Ms. Kitija Alise Štucere Profile

Kitija Alise Štucere

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Publications (3)

Proceedings Article | 30 May 2022 Poster

Carbene-metal complexes as through-space TADF emitters

Kitija Štucere, Armands Ruduss, Kaspars Traskovskis, Aivars Vembris

Proceedings Volume PC12149, PC121491F (2022) https://doi.org/10.1117/12.2621975

KEYWORDS: Temperature metrology, Quantum efficiency, Metals, Thin films, Luminescence, Copper, Chemical species, System on a chip, Scattering, Phosphorescence

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Materials for organic light-emitting diodes could be divided into several generations were last 3rd generation organic compounds exhibiting TADF which exhibit up to 100% singlet and triplet state conversation to light without the presence of heavy metal. Organometallic complexes consisting of Cu metal atom is a conceptually different class of low-cost TADF emitters. While this element does not exhibit fast room-temperature phosphorescence, it still can promote a rapid TADF, despite the considerable ΔEST gaps met in such compounds (< 0.05 eV). In this work, we present a novel approach towards TADF emitters where charge transfer through-space and metal-assisted take place. Cu complexes bearing carbazolide and carbene ligands were synthesized. Imidazole-based N-heterocyclic carbenes (NHCs) were used, with electron-accepting sulphonyl groups introduced at 4-position of the N-bound 2,6-diisopropylphenyl (Dipp) substituents. Photoluminescence bands, decays and quantum yields of complexes in various solutions, as well as PMMA-doped films with emitter concentration 5 wt%, were taken. Emission properties of thin films in the temperature diapason from 10 to 300 K were measured to estimate the charge transfer mechanism. For PL bands at room temperature excitation wavelength was either 300 or 375 nm. For temperature-induced CT emission band shifts in vacuum 345 nm excitation wavelength was used, delay 50 ns and width 10 μs. To get PL decays at room temperature a laser with a wavelength of 375 nm was used and decay was measured at the peak wavelength. For temperature-induced decays in vacuum used excitation was 345 nm, time range 50 µs. To get quantum yields at room temperature, emission and scattering ranges of the sample were measured separately with 375 nm excitation. Photoluminescence quantum yield from 0.2 to 0.3 was obtained in solutions but in thin films, it increased up to 0.9 due to the decreased torsional degree of freedom. Emission decays could be described by three exponential functions in all temperature intervals. One featuring a prompt and two delayed emission components. For both delayed emissions, the fastest and slowest emission rate decrease is observed throughout the cooling range, designating a thermally activated nature of the emissive process. The corresponding ΔEST values were estimated from Arrhenius plots and are in the range of 0.0062−0.0075 eV. By combining through-space CT architecture, giving compounds the characteristic low ΔEST values, with the presence of a heavy metal atom, which provides small, but still present SOC.