Once considered the exclusive property of metal complexes, the phenomenon of room-temperature phosphorescence (RTP) has been increasingly realized in pure organic luminophores recently. Using precise ...molecular design and synthetic approaches to modulate their weak spin-orbit coupling, highly active triplet excitons, and ultrafast deactivation, organic luminophores can be endowed with long-lived and bright RTP characteristics. This has sparked intense explorations into organic luminophores with enhanced RTP features for different applications. This Review discusses the fundamental mechanism of RTP in pure organic luminophores, followed by design principles, enhancement strategies, and formulation methods to achieve highly phosphorescent and long-lived organic RTP luminophores even in aqueous media. The current challenges and future directions of this field are also discussed in the summary and outlook.
Commercial carbazole has been widely used to synthesize organic functional materials that have led to recent breakthroughs in ultralong organic phosphorescence
, thermally activated delayed ...fluorescence
, organic luminescent radicals
and organic semiconductor lasers
. However, the impact of low-concentration isomeric impurities present within commercial batches on the properties of the synthesized molecules requires further analysis. Here, we have synthesized highly pure carbazole and observed that its fluorescence is blueshifted by 54 nm with respect to commercial samples and its room-temperature ultralong phosphorescence almost disappears
. We discover that such differences are due to the presence of a carbazole isomeric impurity in commercial carbazole sources, with concentrations <0.5 mol%. Ten representative carbazole derivatives synthesized from the highly pure carbazole failed to show the ultralong phosphorescence reported in the literature
. However, the phosphorescence was recovered by adding 0.1 mol% isomers, which act as charge traps. Investigating the role of the isomers may therefore provide alternative insights into the mechanisms behind ultralong organic phosphorescence
.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Chemical modification of phenothiazine‐benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state. A ...fundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively. Time‐resolved spectroscopy and time‐dependent density functional theory (TD‐DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics. This has resulted in a RTP molecule OPM, where the triplet states contribute with 89 % of the luminescence, and an isomeric TADF molecule OMP, where the triplet states contribute with 95 % of the luminescence.
Rapid and efficient utilization of triplet states to generate room temperature phosphorescence (RTP) or highly efficient thermally activated delayed fluorescence (TADF) is achieved by structural modification to give a planar or twisted intramolecular charge transfer (PICT or TICT) geometry, respectively.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Near infrared (NIR) light excitable photosensitizers are highly desirable for photodynamic therapy with deep penetration. Herein, a NIR‐II light (1200 nm) activated photosensitizer TQ‐BTPE is ...designed with aggregation‐induced singlet oxygen (1O2) generation for two‐photon photodynamic cancer cell ablation. TQ‐BTPE shows good two‐photon absorption and bright aggregation‐induced NIR‐I emission upon NIR‐II laser excitation. The 1O2 produced by TQ‐BTPE in an aqueous medium is much more efficient than that of commercial photosensitizer Ce6 under white light irradiation. Upon NIR‐II excitation, the two‐photon photosensitization of TQ‐BTPE is sevenfold higher than that of Ce6. The TQ‐BTPE molecules internalized by HeLa cells are mostly located in lysosomes as small aggregate dots with homogeneous distribution inside the cells, which favors efficient photodynamic cell ablation. The two‐photon photosensitization of TQ‐BTPE upon NIR‐I and NIR‐II excitation shows higher 1O2 generation efficiency than under NIR‐I excitation owing to the larger two‐photon absorption cross section at 920 nm. However, NIR‐II light exhibits better biological tissue penetration capability after passing through a fresh pork tissue, which facilitates stronger two‐photon photosensitization and better cancer cell ablation performance. This work highlights the promise of NIR‐II light excitable photosensitizers for deep‐tissue photodynamic therapy.
An aggregation‐induced emission photosensitizer (TQ‐BTPE) with good two‐photon absorption and high singlet oxygen generation is synthesized for NIR‐II light (1200 nm) activated two‐photon photodynamic therapy, which exhibits better tissue penetration and more precise cancer cell ablation than NIR‐I light.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A novel white‐light‐emitting organic molecule, which consists of carbazolyl‐ and phenothiazinyl‐substituted benzophenone (OPC) and exhibits aggregation‐induced emission‐delayed fluorescence (AIE‐DF) ...and mechanofluorochromic properties was synthesized. The CIE color coordinates of OPC were directly measured with a non‐doped powder, which presented white‐emission coordinates (0.33, 0.33) at 244 K to 252 K and (0.35, 0.35) at 298 K. The asymmetric donor–acceptor–donor′ (D‐A‐D′) type of OPC exhibits an accurate inherited relationship from dicarbazolyl‐substituted benzophenone (O2C, D‐A‐D) and diphenothiazinyl‐substituted benzophenone (O2P, D′‐A‐D′). By purposefully selecting the two parent molecules, that is, O2C (blue) and O2P (yellow), the white‐light emission of OPC can be achieved in a single molecule. This finding provides a feasible molecular strategy to design new AIE‐DF white‐light‐emitting organic molecules.
Like fluorescent butterflies: A single white‐light‐emitting organic compound with aggregation‐induced emission‐delayed fluorescence (AIE‐DF) was achieved by selection of the parent molecules. This novel design principle is a form of molecular inheritance of the tuning properties for a targeted molecule.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photoluminescence quantum yield (PLQY) is one of the most important characteristics for organic luminescent materials. However, when carbazole prepared from the lab was compared to that from a ...commercial source, a remarkable change of PLQY was observed to vary from 37.1% to 69.8%. Taking 9-(4-bromobenzyl)-9H-carbazole (CzBBr) as an example of carbazole derivatives, the PLQYs of CzBBr synthesized from different origins of carbazole were varied from 16.0% to 91.1%. Our studies demonstrated that efficient radiative transition pathways were activated for commercial carbazole based luminescence, leading to a large enhancement in PLQY with fluorescence (from 16.0% to 54.4%) and phosphorescence (from <1% to 36.7%) for CzBBr. These results suggest that the origin of carbazole plays a very important role in determining the optical properties of carbazole derivatives, alerting us to carefully revisit carbazole and its derivatives, especially those with record-high efficiency.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
Doping has shown very promising potential in endowing room‐temperature phosphorescence (RTP) properties of organic phosphors with minimal effort. Here, a new isomer design and doping strategy is ...reported that is applicable to dibenzothiophene (DBT) and its derivatives. Three isomers are synthesized to study the dopant effect on enhancing RTP of DBT derivatives. It is found that isomer dopants bearing close resemblance to the host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy difference between singlet‐ and triplet‐excited states can yield efficient RTP for the doped system. Meanwhile, phosphorescence color from yellow to red is achieved by varying isomer dopants used for doping the DBT derivatives. This work represents an RTP enhancement strategy based on isomer design and doping to construct luminescent organic phosphors.
An efficient doping strategy is applied to endow bright room‐temperature phosphorescence (RTP) of dibenzothiophene derivatives. The isomer dopants bearing close resemblance to host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy gap between singlet‐ and triplet‐excited states enable bright RTP.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A new ligand containing tetraphenylethylene and terpyridine moieties, and its zinc ion complex were synthesized. Both of them exhibit an aggregation-induced emission effect. Their colors and ...emissions can be smartly switched by various external stimuli including grinding, heating and solvent-fuming, as well as exposure to acid and base vapors.
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