Use of Pyrimidine and Pyrazine Bridges as a Design Strategy To Improve the Performance of Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes

Paloma Lays Dos Santos; Dongyang Chen; Pachaiyappan Rajamalli; Tomas Matulaitis; David B Cordes; Alexandra M Z Slawin; Denis Jacquemin; Eli Zysman-Colman; Ifor D W Samuel

doi:10.1021/acsami.9b16952

Use of Pyrimidine and Pyrazine Bridges as a Design Strategy To Improve the Performance of Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes

ACS Appl Mater Interfaces. 2019 Dec 4;11(48):45171-45179. doi: 10.1021/acsami.9b16952. Epub 2019 Nov 21.

Authors

Paloma Lays Dos Santos¹, Dongyang Chen², Pachaiyappan Rajamalli², Tomas Matulaitis², David B Cordes², Alexandra M Z Slawin², Denis Jacquemin³, Eli Zysman-Colman², Ifor D W Samuel¹

Affiliations

¹ Organic Semiconductor Centre, SUPA, School of Physics and Astronomy , University of St Andrews , St Andrews, Fife KY16 9SS , United Kingdom.
² Organic Semiconductor Centre, EaStCHEM School of Chemistry , University of St. Andrews , St. Andrews, Fife KY16 9ST , United Kingdom.
³ CEISAM, UMR-CNRS 6230 , University of Nantes , 2 rue de la Houssinière , 44322 Nantes , France.

PMID: 31697057
DOI: 10.1021/acsami.9b16952

Abstract

We present a study of two isomeric thermally activated delayed fluorescence (TADF) emitters 9,9'-(sulfonylbis(pyrimidine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole) (pDTCz-DPmS) and 9,9'-(sulfonylbis(pyrazine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole) (pDTCz-DPzS). The use of pyrimidine and pyrazine as bridging units between the electron donor and acceptor moieties is found to be advantageous compared to the phenyl- (pDTCz-DPS) and pyridine-based analogues (pDTCz-3DPyS and pDTCz-2DPyS). Conformational modulation of the donor groups as a function of the bridge results in high photoluminescence quantum yields (Φ_PL > 68%) and small energy gaps between singlet and triplet excited states (ΔE_ST < 160 meV). OLEDs using pDTCz-DPmS and pDTCz-DPzS as emitters exhibit blue and green electroluminescence, respectively, with higher maximum external quantum efficiencies (EQE_max of 14% and 18%, respectively) and a reduced efficiency roll-off as compared to the reference devices using pDTCz-DPS, pDTCz-3DPyS, and pDTCz-2DPyS as the emitters. Our results provide a more complete understanding on the impact of the bridge structure in D-A-D TADF systems on the optoelectronic properties of the emitter and how the balance between color purity and EQE in the devices can be controlled, advancing the design strategies for TADF emitters.

Keywords: TADF; blue OLED; intramolecular hydrogen bond; organic light emitting diodes; pyrazine; pyrimidine.