Achieving Purely Organic Room-Temperature Phosphorescence Mediated by a Host-Guest Charge Transfer State

作者：Qiu, Weidong; Cai, Xinyi; Li, Mengke; Chen, Zijian; Wang, Liangying; Xie, Wentao; Liu, Kunkun; Liu, Ming; Su, Shi-Jian^*

来源：Journal of Physical Chemistry Letters, 2021, 12(19): 4600-4608.

DOI：10.1021/acs.jpclett.1c01095

• TRIPLET EXCITED-STATES
• LIGHT-EMITTING-DIODES
• ENERGY-TRANSFER
• PERSISTENT
• PHOTOLUMINESCENCE
• EXCIPLEXES
• MOLECULES
• AFTERGLOW

Strategies for developing purely organic materials exhibiting both high efficiency and persistent room-temperature phosphorescence (RTP) have remained ambiguous and challenging. Herein, we propose that introducing an intermediate charge transfer (CT) state into the donor-acceptor binary molecular system holds promise for accomplishing this goal. Guest materials showing gradient ionization potentials were selected to fine-tune the intermolecularly formed CT state when doped into the same host material with a large electron affiliation potential. Such a CT intermediate state accelerates the population of the triplet exciton to benefit phosphorescent emission and decreases the phosphorescence lifetime via quenching the long-lived triplet excitons. As a result, a "trade-off" between a long phosphorescence lifetime (595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained by tuning the host-guest energy gap offset. This finding highlights the key role of CT in RTP emission and provides new guidance for developing novel RTP systems.