TY - JOUR
T1 - Emission properties of thermally activated delayed fluorescence emitters
T2 - Analysis based on a four-level model considering a higher triplet excited state
AU - Kobayashi, Takashi
AU - Niwa, Akitsugu
AU - Haseyama, Shota
AU - Takaki, Kensho
AU - Nagase, Takashi
AU - Goushi, Kenichi
AU - Adachi, Chihaya
AU - Naito, Hiroyoshi
N1 - Funding Information:
This work was supported in part by a Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science: Grants Nos. 17H01265, 15H03883, 17K18993, and 15J12038.
Publisher Copyright:
© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).
PY - 2018/7/1
Y1 - 2018/7/1
N2 - A four-level model consisting of a higher triplet excited state (T2), the lowest singlet and triplet excited states (S1 and T1), and the ground state was previously used to understand emission properties of a thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). In this report, we discuss the four-level model in more detail and apply to the other two TADF emitters, i.e., 1,2,4,5-tetrakis(carbazol-9-yl)-3,6-dicyanobenzene (4CzTPN) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), in order to determine their excited-state structures. It is suggested that in all the emitters T2 lies between S1 and T1 and play an essential role in the emitting process. In 4CzTPN, phosphorescence from T2 is clearly observed around 100 K as in 4CzIPN. Compared to the other two emitters, 2CzPN has a wider energy gap between S1 and T1 so that delayed fluorescence at room temperature is thought to be mixed with phosphorescence. Because of this mixing, the spectrum characteristic of phosphorescence from T2 in 2CzPN cannot be identified.
AB - A four-level model consisting of a higher triplet excited state (T2), the lowest singlet and triplet excited states (S1 and T1), and the ground state was previously used to understand emission properties of a thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). In this report, we discuss the four-level model in more detail and apply to the other two TADF emitters, i.e., 1,2,4,5-tetrakis(carbazol-9-yl)-3,6-dicyanobenzene (4CzTPN) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), in order to determine their excited-state structures. It is suggested that in all the emitters T2 lies between S1 and T1 and play an essential role in the emitting process. In 4CzTPN, phosphorescence from T2 is clearly observed around 100 K as in 4CzIPN. Compared to the other two emitters, 2CzPN has a wider energy gap between S1 and T1 so that delayed fluorescence at room temperature is thought to be mixed with phosphorescence. Because of this mixing, the spectrum characteristic of phosphorescence from T2 in 2CzPN cannot be identified.
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U2 - 10.1117/1.JPE.8.032104
DO - 10.1117/1.JPE.8.032104
M3 - Article
AN - SCOPUS:85042628504
VL - 8
JO - Journal of Photonics for Energy
JF - Journal of Photonics for Energy
SN - 1947-7988
IS - 3
M1 - 032104
ER -