Abstract
Organic room temperature phosphorescence (RTP) materials have received considerable attention due to their fascinating photophysical properties. During the past decade, various organic luminogens exhibiting RTP emission in solid states were reported. However, the phosphorescence emission of organic compounds can hardly be observed in their solutions at room temperature. Herein, we reported two fluorene derivatives that can emit RTP in degassed organic solvents, polymer doped film, and crystalline states. Furthermore, those RTP luminogens emitted different colors with different phosphorescence lifetimes in multi-states. These results indicated that the phosphorescence performance can be adjusted flexibly in different condensed states. To our knowledge, this is the first example possessing diverse organic RTP at multi-states, including solution state.
Highlights
The most reported organic luminogens emitting phosphorescence are in solid states at room temperature or in solution state at 77 K, owing to the unstable triplet excited states, which can be quenched by molecular vibration and the collision with other media
The phosphorescent intensity of the two compounds at the maximum emission peak is proportional to the concentration of the solutions (Supplementary Figure S13), suggesting that the phosphorescent emission originates from the monomeric species and no molecular interactions existed in solution
The phosphorescence lifetime at room temperature ranges from microseconds to milliseconds
Summary
Organic RTP attracts tremendous attention because of its unique characters, especially the long-lived triplet states, and exhibits immense potential applications in optoelectronic devices, information encryption, emergency exit sign, chemical sensors, bioimaging, and so on (Lin et al, 2018; Wang et al, 2019b; Gu et al, 2019; He et al, 2019; Yang J. et al, 2020; Yang Z. et al, 2020; Zhao et al, 2020; Liu R. et al, 2021; Garain et al, 2021; Zhu et al, 2021). Su et al prepared a kind of carbon dot composites using a molten salt method, which exhibited bright RTP with a quantum yield of 26.4% and a lifetime of 1.28 s Their aqueous dispersion showed obvious RTP behaviors, and these phosphors were utilized to detect temperature and pH in the aqueous phase (Su et al, 2021). In 2013, Takeuchi et al reported a fluorene derivative substituted by bromo and formyl groups, exhibiting distinct phosphorescence in some common organic solvents at room temperature with the phosphorescence quantum yield of 5.9% in chloroform at 298 K under N2 atmosphere (Xu et al, 2013). This is the first purely organic molecule possessing diverse RTP at multi-states, including solution state
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