A Multi-Functional New Acceptor for Ultra-Broad Multiple Emission, Long-Persistence Thermally Activated Delayed Fluorescence and Room Temperature Phosphorescence

Aiming to design new efficient organic triplet emitters, here a new electron-accepting moiety 11,13-dihydro-12H-dibenzo[a,c]imidazo[4,5-i]phenazin-12-one (BIPO) are reported. Three new BIPO derivatives containing long alkyl chains, namely DBIPO (acceptor only), DBIPOBr (acceptor containing bromine atoms), and DBIPOAc with acridan moieties in a donor-acceptor-donor configuration, are designed and investigated. Efficient room temperature phosphorescence (RTP) is detected for the three compounds, stemming from a high-lying (anti-Kasha type) triplet emission occurring in the acceptor moiety. Additionally, the tetrahydrofuran- and dichloromethane DBIPOAc solutions show (i) a dual-band photoluminescence profile stemming from anti-Kasha emissions from high-lying charge-transfer (1CT) and locally excited (1LE) states, and (ii) a thermally activated delayed fluorescence (TADF) from the same high-lying 1CT state. Importantly, DBIPOAc doped in rigid nonpolar polymer Zeonex simultaneously exhibits both TADF and RTP, with the emission quantum yield reaching 69.6%. Due to these properties, the BIPO derivatives constitute promising candidates as multi-functional new emitters for the preparation of active layers of electroluminescent devices and optical oxygen/pressure sensors. The reasons for these interesting properties are discussed in detail.