The project was carried out along clear research directions addressing two objectives following the bottom-up approach. The development of NIR p-RTP emission has been achieved by trace doping and uniform dispersion of small molecules in highly packed and rigid host matrices. The main work performed includes:
Development of small molecule-based host/guest p-RTP material systems. After careful material screening, boronic ester-based molecules were selected as guest molecules, with TPO, BP, and PPT as small-molecule hosts. Photophysical characterization confirmed strong p-RTP properties in phenothiazine-based boronic ester systems, with RTP lifetimes increasing from 30 ms (in TPO) to over 300 ms (in PPT). The enhanced performance is attributed to improved spin-orbit coupling and suppressed non-radiative decay as well as the distribution of host-guest triplet excited states, emphasizing the role of molecular engineering in advancing organic p-RTP materials for optoelectronics.
Development of polymer-based host/guest NIR p-RTP material systems. 1) A phosphole molecule (pyrene-substituted azaphosphole) was presented, exhibiting RTP emission beyond 600 nm with a 300 ms lifetime but low photoluminescence quantum yield (PLQY <2%), likely due to phosphorus's heavy atom effect. We established design principles for future applications. 2) Expanding the previous cycloaddition method, a series of diazaphospholes were synthesized, achieving strong fluorescence with PLQYs up to 37%, making them promising for optoelectronics. 3) A supramolecular foldamer was designed, showing a face-to-face donor-acceptor stacking through non-covalent interactions. Confirmed by NMR and single-crystal analysis, it exhibits single-molecule exciplex thermally activated delayed fluorescence in solution and deep-blue RTP with a 236 ms afterglow in a PMMA matrix, setting a record lifetime for triplet charge transfer-character RTP. 4) By employing strong RTP emitters and fluorescence dyes as the donor and acceptor molecules, respectively, we successfully achieved efficient deep-red persistent emission via the triplet-singlet Fӧrster resonance energy transfer (TS-FRET) mechanism. The system reached a phosphorescence QY of 53.6% (10 wt% TA) and maintained 37.2% at 30 wt%. Total PLQY increased to 85.7% at 20 wt% TA.
Implement NIR p-RTP into applications. After trying and analyzing, a fully functional device is yet to be achieved. But the polymer host limitations with poor charge mobility were identified. Instead, I gained training in OLED simulation with SIMOJI tools and also came up with new ideas to fabricate OLEDs and expand the applications.
Based on the research, tunable NIR p-RTP in purely organic systems were demonstrated, establishing new molecular design principles for future materials. The results also contributed to the fundamental understanding of triplet exciton dynamics and generated new possibilities for applications. Three papers have been published: Chem, 2024, 10 (2), 644-659, Inorg. Chem. Front., 2025,
https://doi.org/10.1039/D5QI00427F(se abrirá en una nueva ventana) Adv. Optical Mater., 2024, 2400210; one paper submitted to J. Mater. Chem. C.
