Tunable Ultralong Organic Room-Temperature Phosphorescence of Dinaphthylamine Skeleton via Molecular Modification and Conformational Change in a Flexible Cross-Linked Polymer Network

Herein, we developed a simple cross-linking strategy to fabricate a flexible PETA/MA polymer network featuring tunable ultralong organic room-temperature phosphorescence (UORTP). Three dinaphthylamine-structured phosphorescence molecules (NQA-1, NQA-2, and NQA-3), modified with an (iso)quinoline ring, were synthesized, and the tiny structural change made a great difference to their UORTP properties by controlling T₁ excited states and intersystem crossing (ISC) efficiency. We thoroughly studied the UORTP performance in toluene solution, in PMMA film, in non-cross-linked copolymerized films, and in cross-linked films with three different cross-linkers. In particular, the PETA/MA films can be prepared via 30-s photopolymerization, which greatly reduces possible photobleaching. When the weight ratio of pentaerythritol tetraacrylate (PETA) increased from 0 to 0.06, the phosphorescence lifetime of NQA-1 was prolonged from 120 ms to 1.07 s, and the optimal ratio was determined to be 0.04. As the cross-linking density increased gradually, the glass-transition temperature (T_g) rose, and the free volume reduced, which significantly prohibited nonradiative relaxation and led to high-performance UORTP. Moreover, the 0.04PETA/MA film possessed high flexibility. In the 0.04PETA/MA film, NQA-1 and NQA-3 showed remarkable phosphorescence redshift, while NQA-2 displayed a unique phosphorescence blueshift, suggesting that the cross-linked network significantly influences the molecular conformation and subsequently tunes the phosphorescence color. Therefore, molecular structural modification and molecular conformational change are both involved in regulating UORTP in this work. We believe that this study will pave a simple way for future applications of polymeric phosphorescence materials.