Hot exciplexes in U-shaped TADF molecules with emission from locally excited states

A Lennart Schleper,Bastian Haehnle,Chihaya Adachi,Kenichi Goushi,Alexander J C Kuehne,Philipp J Welscher,Christoph Bannwarth

doi:10.1038/s41467-021-26439-w

Abstract

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T1 to T2 spacing. The hot exciplex model is investigated using optical spectroscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T3 to the S1 state within only a few nanoseconds. Application and practicality of the model are shown by fabrication of organic light-emitting diodes with up to 32 % hot exciplex contribution and low efficiency roll-off.

Highlights

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs)
We aim at aligning CT and LE states to enable spin–orbit coupling between excited triplet and excited singlet states and to promote fast RISC33–35
The subscript b indicates that this state is localized on the anthracene bridge. e U-shaped hot exciton design, containing an anthracene unit which holds the LE and bridges the donors and acceptor moieties

Summary

Introduction

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). While both donor and acceptor possess locally excited singlet states (1LE), the emission occurs from the generated exciplex charge transfer singlet state 1CT (see Fig. 1b)[9]. One strategy to overcome this problem is via hot triplet excitons that enable upper-level RISC, evading limitation to emissive 1CT states of conventional TADF materials (see Fig. 1c)[12,13,14].

Results

Conclusion