The development of purely organic emitters that can efficiently harvest the triplet excited states has been an active research area in the past few years. However, the major challenges are controlling the nonradiative deactivation of the triplet excited states and tuning the singlet-triplet energy gap (ΔEST). To tune the thermally activated delayed fluorescence (TADF) and the room temperature phosphorescence (RTP) via triplet harvesting, we developed a new class of multichromophoric tridonor-acceptor (D3-A) compounds with N-rich rigid and flexible π-spacer having pyridoquinoxaline (PQ) and pyridopyrazine (PZ) acceptor core, respectively. The different charge transfer (CT) interactions due to donors at different positions in rigid PQ core facilitate the reverse intersystem crossing (RISC) leading to TADF. Whereas, D3-A molecules with donors on twisted and flexible acceptor core, PZ exhibit prominent RTP due to relatively higher ΔEST value. The lower ΔEST value was observed by increasing the donor strength in the PZ system leading to simultaneous TADF and RTP emission. Further, the multiple redox centers were created by incorporating easily oxidizable donors on different derivatives of rigid PQ cores. The color of the D-A compounds was tuned by electric stimuli. The electrochemical analysis, coupled with time-resolved spectroscopic measurements, indicates the potential electrofluorochromism in PQ-based D-A compounds. The current study delineating the conformational flexibility of the central acceptor core towards TADF and RTP emission and tuning the color by electronic potential paves the way for further development of multichromophoric materials for photonics applications.

N-Rich electron acceptors: Triplet harvesting in rigid and flexible multichromophoric organic emitters

ACS Spring Meeting 2021

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