The heavy atom effect in halogenated mCP and its influence on the efficiency of the thermally activated delayed fluorescence of dopant molecules
Abstract
In this study, we explore the impact of halogen functionalization on the photophysical properties of the commonly used organic light-emitting diode (OLED) host material, 1,3-bis(N-carbazolyl)benzene (mCP). Derivatives with different numbers and types of halogen substituents on mCP were synthesized. By measuring steady-state and transient photoluminescence at 6 K, we study the impact of the type, number, and position of the halogens on the intersystem crossing and phosphorescence rates of the compounds. In particular, the functionalization of mCP with 5 bromine atoms results in a significant increase of the intersystem crossing rate by a factor of 300 to a value of (1.5 ± 0.1) × 1010 s–1, and the phosphorescence rate increases by 2 orders of magnitude. We find that the singlet radiative decay rate is not significantly modified in any of the studied compounds. In the second part of the paper, we describe the influence of these compounds on the reverse intersystem crossing of the 7,10-bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazino-phenanthrene (TPA-DCPP), a TADF guest, via the external heavy atom effect. Their use results in an increase of the reverse intersystem crossing (RISC) rate from (8.1 ± 0.8) × 103 s–1 for mCP to (2.7 ± 0.1) × 104 s–1 for mCP with 5 bromine atoms. The effect is even more pronounced for the mCP analogue containing a single iodine atom, which gives a RISC rate of (3.3 ± 0.1) × 104 s–1. Time-dependent DFT calculations reveal the importance of the use of long-range corrected functionals to predict the effect of halogenation on the optical properties of the mCP, and the relativistic approximation (ZORA) is used to provide insight into the strength of the spin–orbit coupling matrix element between the lowest-lying excited singlet and triplet states in the different mCP compounds.
Citation
Malinge , A , Kumar , S , Chen , D , Zysman-Colman , E & Kéna-Cohen , S 2024 , ' The heavy atom effect in halogenated mCP and its influence on the efficiency of the thermally activated delayed fluorescence of dopant molecules ' , Journal of Physical Chemistry C , vol. Articles ASAP . https://doi.org/10.1021/acs.jpcc.3c05567
Publication
Journal of Physical Chemistry C
Status
Peer reviewed
ISSN
1932-7447Type
Journal article
Description
S.K.C. acknowledges financial support from the Fonds de Recherche du Québec Nature et Technologies (286499). E.Z.C. acknowledges financial support from the Engineering and Physical Sciences Research Council (EPSRC; EP/R035164/1, EP/P010482/1). S.K. acknowledges the financial support from European Union’s Horizon 2020 research and innovation programme under a Marie-Skłodowska-Curie Individual Fellowship (THF-OLED; Grant Agreement ID 748430).Collections
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