A Class of Organic Units Featuring Matrix-controlled Color-tunable Ultralong Organic Room Temperature Phosphorescence

We for the first time report a novel class of organic units (N-1 and N-2) and their derivatives (PNNA-1 and PNNA-2) with excellent property of ultralong organic room temperature phosphorescence (UORTP). In this work, N-1, N-2 and their derivatives function as the guests while organic powders (PNCz, BBP, DBT) and polymethyl methacrylate (PMMA) serve as the host matrixes. Amazingly, the color of ultralong phosphorescence can be tuned in different states or by varying the host matrixes. At 77 K, all the four molecules show green afterglow in the monomer state but yellow afterglow in the aggregated state because strong intermolecular interactions exist in the self-aggregate and induce a redshift of the afterglow. In particular, PNNA-1 and PNNA-2 demonstrate distinctive photo-activated green UORTP in the PMMA film owing to the generation of their cation radicals. Whereas the PNNA-1@PNCz and PNNA-2@PNCz doping powders give out yellow UORTP, showing matrix-controlled color-tunable UORTP. In the matrix PNCz, the cation radicals of PNNA-1 and PNNA-2 can stay stably and form strong intermolecular interactions with PNCz because of their high molecular structure similarity, leading to a redshift of ultralong phosphorescence. Additionally, PNNA-1 and PNNA-2 show green UORTP in other matrixes DBT and BBP probably because they have a low molecular structure similarity with DBT and BBP. It is exciting that N-1, N-2 and their derivatives perform much better than Bd (H-benzo[f]indole) and its derivatives in UORTP. This study provides another example to support that cation radical might be a universal mechanism in organic phosphorescence. We believe that this work will expand the scope of organic phosphorescence.