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Efficient Direct Reverse Intersystem Crossing between Charge Transfer‐Type Singlet and Triplet States in a Purely Organic Molecule
Author(s) -
Wada Yoshimasa,
Wakisaka Yasuaki,
Kaji Hironori
Publication year - 2021
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.202001013
Subject(s) - intersystem crossing , singlet state , electroluminescence , excited state , photoluminescence , acceptor , oled , triplet state , singlet fission , chemistry , photochemistry , materials science , optoelectronics , molecular physics , atomic physics , physics , nanotechnology , condensed matter physics , layer (electronics)
In the field of organic light‐emitting diodes, thermally activated delayed fluorescence (TADF) materials have achieved great performance. The key factor for this performance is the small energy gap (Δ E ST ) between the lowest triplet (T 1 ) and singlet excited (S 1 ) states, which can be realized in a well‐separated donor‐acceptor system. Such systems are likely to possess similar charge transfer (CT)‐type T 1 and S 1 states. Recent investigations have suggested that the intervention of other type‐states, such as locally excited triplet state(s), is necessary for efficient reverse intersystem crossing (RISC). Here, we theoretically and experimentally demonstrate that our blue TADF material exhibits efficient RISC even between singlet CT and triplet CT states without any additional states. The key factor is dynamic flexibility of the torsion angle between the donor and acceptor, which enhances spin‐orbit coupling even between the charge transfer‐type T 1 and S 1 states, without sacrificing the small Δ E ST . This results in excellent photoluminescence and electroluminescence performances in all the host materials we investigate, with sky‐blue to deep‐blue emissions. Among the hosts investigated, the deepest blue emission with CIE coordinates of (0.15, 0.16) and the highest EQE MAX of 23.9 % are achieved simultaneously.