Abstract
The development of organic luminescent materials with bimodal emissions of both fluorescence and room-temperature phosphorescent (RTP) remains a challenge. The investigation of the relationship between fluorescence and RTP performance is especially rare. In this work, we obtained an organic luminescent molecule, 1,4-phenylenebis((9H-carbazol-9-yl)methanone) (PBCM), which exhibits bimodal emissions of cyan fluorescence and yellow RTP in its crystalline state through adopting an electron donor–acceptor–donor (D–A–D) structure. The charge–transfer (CT) effects in the bimodal luminescent properties of PBCM, as well as the single-crystal structures and thermal properties, were investigated. It was found that the CT effect in the singlet states effectively reduces the ∆Est and promotes the ISC processes, resulting in an efficient phosphorescence of PBCM at room temperature. In addition, many strong intermolecular interactions are formed between the donor and acceptor parts of adjacent molecules, leading to the rigid configurations and compact packing of molecules in crystals, which was also confirmed to facilitate the efficient bimodal emissions of PBCM.
Highlights
Photoluminescence, including fluorescence and phosphorescence, is one of the most active research fields in science and technology today [1,2,3,4]
When the water fraction (f w) was increased to 90 and 99%, the intensity was markedly enhanced, with the tail rising up and extending into the long-wavelength region. These results illustrate that PBCM molecules aggregate into nanoparticles in the THF/water mixed solutions with f w ≥ 90%, which leads to the Mie scattering effect
As for the PL in Figure 1b, some fine vibronic peaks at 343 and 358 nm were observed in pure THF solution, which originated from the localized emission (LE) of PBCM in the mono-molecular state
Summary
Photoluminescence, including fluorescence and phosphorescence, is one of the most active research fields in science and technology today [1,2,3,4]. Organic phosphorescent materials have not achieved the same level of development as fluorescent ones because of the low efficiencies of the triplet state phosphorescence, especially at room temperature [8,9,10]. T1 states have lower energy than S1 states of organic molecules, which results in the further redshift of the phosphorescence emission band compared with the fluorescence bands of the molecules [15]. T1 states have lower energy than S1 states of organic molecu loefs, which results in the further redshift of the phosphorescence emission band compared with the fluorescence bands of the molecules [15]. Tthhee iinnttrroodduuccttiioonn ooff hheeaavvyy aattoommss,, mmeettaall ffrraammeess aanndd hhoosstt––gguueesstt ssyysstteemmss,, tthhee ffoorrmmaattiioonn ooff ssiinnggllee ccrryyssttaallss,, aanndd eemmbbeeddddiinngg iinnttoo aa ppoollyymmeerr mmaattrriixx [[1188––2222]].
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