Abstract
Emitters that exhibit thermally activated delayed fluorescence (TADF) are of interest for commercial applications in organic light-emitting diodes (OLEDs) due to their ability to achieve internal quantum efficiency of 100%. However, beyond the intrinsic properties of these materials it is important to understand how the molecules interact with each other and when these interactions may occur. Such interactions lead to a significant red shift in the photoluminescence and electroluminescence, making them less practicable for commercial use. Through summarizing the literature, covering solid-state solvation effects and aggregate effects in organic emitters, this mini review outlines a framework for the complete study of TADF emitters formed from the current-state-of-the-art techniques.
Highlights
Increasing the efficiency and stability of organic light-emitting diodes (OLEDs) is a focus of significant attention for researchers and one aspect of improving these systems is to produce novel emitters that have internal quantum efficiencies (IQEs) above the 25% dictated by spin statistics (Baldo et al, 1999)
This literature considers the interactions between non-identical molecules to achieve the small exchange energies and high reverse intersystem crossing (rISC) rates required for thermally activated delayed fluorescence (TADF) (Kim et al, 2016; Nakanotani et al, 2016; Sarma and Wong, 2018; Chatterjee and Wong, 2019; Tang et al, 2020) and it has been observed that host–guest interactions can imbue functional properties (Matsunaga and Yang, 2015; Feng et al, 2017; Ono et al, 2018)
The review will reflect on the discovery of functional behavior in existing compounds, especially 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN)–an archetypal TADF emitter (Uoyama et al, 2012) and how this may influence the interpretation of previous results highlighting the two effects related to the red shifting of emission with concentration: solid-state solvation effect (SSSE) and aggregation
Summary
Increasing the efficiency and stability of organic light-emitting diodes (OLEDs) is a focus of significant attention for researchers and one aspect of improving these systems is to produce novel emitters that have internal quantum efficiencies (IQEs) above the 25% dictated by spin statistics (Baldo et al, 1999). It must be noted that there is an extensive field of research into exciplex systems and controlling fluorescence behavior through host–guest interactions, where intermolecular interactions are embraced This literature considers the interactions between non-identical molecules to achieve the small exchange energies and high rISC rates required for TADF (Kim et al, 2016; Nakanotani et al, 2016; Sarma and Wong, 2018; Chatterjee and Wong, 2019; Tang et al, 2020) and it has been observed that host–guest interactions can imbue functional properties (Matsunaga and Yang, 2015; Feng et al, 2017; Ono et al, 2018). The review will reflect on the discovery of functional behavior in existing compounds, especially 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN)–an archetypal TADF emitter (Uoyama et al, 2012) and how this may influence the interpretation of previous results highlighting the two effects related to the red shifting of emission with concentration: solid-state solvation effect (SSSE) and aggregation
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