Solvent Effect on Thermally Activated Delayed Fluorescence by 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene

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• 作者：Ryoichi Ishimatsu ; Shigeyuki Matsunami ; Katsuyuki Shizu ; Chihaya Adachi ; Koji Nakano ; Toshihiko Imato
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：July 11, 2013
• 年：2013
• 卷：117
• 期：27
• 页码：5607-5612
• 全文大小：293K
• 年卷期：v.117,no.27(July 11, 2013)
• ISSN：1520-5215

文摘

Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T₁) to the singlet excited state (S₁), where these states are separated by a small energy gap (螖E_st), followed by a radiative transition to the ground state (S₀). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol, and acetonitrile). We revealed that the rate constant of RISC, k_RISC, which is the most important factor for TADF, was significantly enhanced by a reduced 螖E_st in more polar solvents. The smaller 螖E_st was mainly attributable to a stabilization of the S₁ state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S₁ and S₀ states (17 D). Despite of this factor, we observed a negative correlation between 螖E_st and efficiency of the delayed fluorescence (_d). This was ascribed to a lower intersystem crossing rate, k_ISC, and increased nonradiative decay from S₁, k_nr^s, in polar solvents.