20 February 2018 Emission properties of thermally activated delayed fluorescence emitters: analysis based on a four-level model considering a higher triplet excited state
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Abstract
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.
© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
Takashi Kobayashi, Takashi Kobayashi, Akitsugu Niwa, Akitsugu Niwa, Shota Haseyama, Shota Haseyama, Kensho Takaki, Kensho Takaki, Takashi Nagase, Takashi Nagase, Kenichi Goushi, Kenichi Goushi, Chihaya Adachi, Chihaya Adachi, Hiroyoshi Naito, Hiroyoshi Naito, } "Emission properties of thermally activated delayed fluorescence emitters: analysis based on a four-level model considering a higher triplet excited state," Journal of Photonics for Energy 8(3), 032104 (20 February 2018). https://doi.org/10.1117/1.JPE.8.032104 . Submission: Received: 26 November 2017; Accepted: 25 January 2018
Received: 26 November 2017; Accepted: 25 January 2018; Published: 20 February 2018
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