Long-lived Room-temperature Phosphorescence Research Articles

Theoretical Insight Into the Ultralong Room-Temperature Phosphorescence of Nonplanar Aromatic Hydrocarbon.

Purely aromatic hydrocarbon materials with ultralong room-temperature phosphorescence (RTP) were reported recently, but which is universally recognized as unobservable. To reveal the inherent luminescent mechanism, two compounds, i.e., PT with a faint RTP and HD with strong RTP featured by nonplanar geometry, were chosen as a prototype to study their excited-state electronic structures by using quantum mechanics/molecular mechanics (QM/MM) model. It is demonstrated that the nonplanar ethylene brides can offer σ-electron to strengthen spin-orbit coupling (SOC) between singlet and triplet excited states, which can not only promote intersystem crossing (ISC) of S1→Tn to increase the population of triplet excitons, but also accelerate the radiative decay rate of T1→S0, and thus improving RTP. Impressively, the nonradiative decay rate only has a small increase, owing to the synergistic effect between the increase of SOC and the reduction of reorganization energy of T1→S0 caused by the restricted torsional motions of aromatic rings. Therefore, a bright and long-lived RTP was obtained in aromatic hydrocarbon materials with twisted structure. This work provided a new insight into the ultralong RTP in pure organic materials.

Large-Area, Flexible, Transparent, and Long-Lived Polymer-Based Phosphorescence Films.

Polymer-based room-temperature phosphorescence (RTP) materials with high flexibility and large-area producibility are highly promising for applications in organic electronics. However, achieving such photophysical materials is challenging because of difficulties in populating and stabilizing susceptible triplet excited states at room temperature. Herein large-area, flexible, transparent, and long-lived RTP systems prepared by doping rationally selected organic chromophores in a poly(vinyl alcohol) (PVA) matrix were realized through a hydrogen-bonding and coassembly strategy. In particular, the 3,6-diphenyl-9H-carbazole (DPCz)-doped PVA film shows long-lived phosphorescence emission (up to 2044.86 ms) and a remarkable duration of afterglow (over 20 s) under ambient conditions. Meanwhile, the 7H-dibenzo[c,g]carbazole (DBCz)-doped PVA film exhibits high absolute luminance of 158.4 mcd m2 after the ultraviolet excitation source is removed. The RTP results not only from suppressing the nonradiative decay by abundant hydrogen-bonding interactions in the PVA matrix but also from minimizing the energy gap (ΔEST) between the singlet state and the triplet state through the coassembly effect. On account of the outstanding mechanical properties and the afterglow performance of these RTP materials, they were applied in the fabrication of flexible 3D objects with repeatable folding and curling properties. Importantly, the multichannel afterglow light-emitting diode arrays were established under ambient conditions. The present long-lived phosphorescent systems demonstrate a bright opportunity for the production of large-area, flexible, and transparent emitting materials.

Hydrothermal Synthesis of Zinc-Doped Silica Nanospheres Simultaneously Featuring Stable Fluorescence and Long-Lived Room-Temperature Phosphorescence.

Fluorescence and phosphorescence are known as two kinds of fundamental optical signals, which have been used for myriad applications. To date, simultaneous activation of stable fluorescence and long-lived room-temperature phosphorescence (RTP) emission in the aqueous phase remains a big challenge. We prepare zinc-doped silica nanospheres (Zn@SiNSs) with fluorescence and RTP properties using a facile hydrothermal synthetic strategy. For the as-prepared Zn@SiNSs, the recombination of electrons and holes in defects and defect-stabilized excitons derived from oxygen vacancy/C=N bonds lead to the production of stable fluorescence and long-lived RTP (emission lasting for ≈9 s, quantum yield (QY): ≈33.6 %, RTP lifetime: ≈236 ms). The internal Si-O bonded networks and hydrophilic surface in Zn@SiNSs can reduce nonradiative decay to form self-protective RTP, and also provide high water solubility, excellent pH- and photostability.

Long-Lived Room-Temperature Phosphorescence of Arene–Beta-Cyclodextrin–Hydrocarbon Complexes in the Presence of Oxygen

Long-Lived Room-Temperature Phosphorescence of Arene–Beta-Cyclodextrin–Hydrocarbon Complexes in the Presence of Oxygen

Inside Back Cover: Ultralong Room‐Temperature Phosphorescence from Boric Acid (Angew. Chem. Int. Ed. 17/2021)

The impressive and unexpected long-lived room-temperature phosphorescence of boric acid (H3BO3) is unveiled by Peng Wu and co-workers in their Research Article on page 9500. Unlike traditional metallic inorganic or aromatic organic phosphors, the phosphorescence originates from the weak conjugation of lone pair electrons from O atoms. The vacant pz orbital of B and the regular arrangement in the crystalline state with layer-like packing through abundant hydrogen bonding are found to contribute to the long-lived emission.

Ultralong Room-Temperature Phosphorescence from Boric Acid.

For a long time, phosphors with long-lived emission are dominated by rare earth/transition metal ion-doped sulfides and oxides. Recently, organic materials capable of emitting long-lived room-temperature phosphorescence (RTP) are reported, carbon skeletons are almost the exclusive structural feature of the conjugated luminophores. Herein, we reported that boric acid, a non-metal and C-free material, could emit RTP with lifetime up to 0.3 s. Detailed investigations indicated the weak conjugation between the n electrons of the O atoms in the B-O confined space was the possible origin of RTP. Similar RTP was also found in electron-rich N/F systems, namely, BN and BF3 (BF4 - ). Importantly, the vacant orbital of B was found to contribute to the relevant unoccupied molecular orbitals involved in excitation, which is different from previous reports on phosphorescence from arylboronic acids. The results confirm the unique role of B as a versatile structure motif for construction of new RTP materials.

Donor–acceptor structure of a coordination polymer with long-lived room temperature phosphorescence and angle-dependent polarized emission

The formation of a donor–acceptor structure in a coordination polymer results in a long room temperature phosphorescence lifetime (40.22 ms) three orders of magnitude higher than that of pristine phosphor.

Simple Vanilla Derivatives for Long-Lived Room-Temperature Polymer Phosphorescence as Invisible Security Inks.

Developing novel long-lived room-temperature polymer phosphorescence (RTPP) materials could significantly expand their application scope. Herein, a series of RTPP materials based on eight simple vanilla derivatives for security ink application are reported. Attributed to strong mutual hydrogen bonding with polyvinyl alcohol (PVA) matrix, vanilla-doped PVA films exhibit ultralong phosphorescence emission under ambient conditions observed by naked eyes, where methyl vanillate shows the longest emission time up to 7 s. Impressively, when vanilla-doped PVA materials are utilized as invisible security inks, and the inks not only present excellent luminescent emission stability under ambient conditions but also maintain perfect reversibility between room temperature and 65°C for multiple cycles. Owing to the unique RTPP performance, an advanced anticounterfeiting data encoding/reading strategy based on handwriting technology and complex pattern steganography is developed.

Long-lived room temperature phosphorescence of organic–inorganic hybrid systems

This review highlights the important role of several organic–inorganic hybrid systems. The fundamental mechanism, design principles, and enhancement strategies to achieve high performance room temperature phosphorescence have been discussed.

σ‐Conjugation and H‐Bond‐Directed Supramolecular Self‐Assembly: Key Features for Efficient Long‐Lived Room Temperature Phosphorescent Organic Molecular Crystals

Long-lived room temperature phosphorescence from organic molecular crystals attracts great attention. Persistent luminescence depends on the electronic properties of the molecular components, mainly π-conjugated donor-acceptor (D-A) chromophores, and their molecular packing. Here, a strategy is developed by designing two isomeric molecular phosphors incorporating and combining a bridge for σ-conjugation between the D and A units and a structure-directing unit for H-bond-directed supramolecular self-assembly. Calculations highlight the critical role played by the two degrees of freedom of the σ-conjugated bridge on the chromophore optical properties. The molecular crystals exhibit RTP quantum yields up to 20 % and lifetimes up to 520 ms. The crystal structures of the efficient phosphorescent materials establish the existence of an unprecedented well-organization of the emitters into 2D rectangular columnar-like supramolecular structure stabilized by intermolecular H-bonding.

Molecular Engineering through Control of Structural Deformation for Highly Efficient Ultralong Organic Phosphorescence.

It is an enormous challenge to achieve highly efficient organic room-temperature phosphorescence (RTP) with a long lifetime. We demonstrate that, by bridging the carbazole and halogenated phenyl ring with a methylene linker, RTP phosphors CzBX (X=Cl, Br) present high phosphorescence efficiency (ΦPh ). A ΦPh up to 38 % was obtained for CzBBr with a lifetime of 220 ms, which is much higher than that of compounds CzPX (X=Cl, Br) with a C-N bond as a linker (ΦPh <1 %). Single-crystal analysis and theoretical calculations revealed that, in the crystal phase, intermolecular π-Br interactions accelerate the intersystem crossing process, while tetrahedron-like structures induced by sp3 methylene linkers restrain the nonradiative decay channel, leading to the high phosphorescence efficiency in CzBBr. This research paves a new road toward highly efficient and long-lived RTP materials with potential applications in anti-counterfeiting or data encryption.

Photo-Stimulated Polychromatic Room Temperature Phosphorescence of Carbon Dots.

Single-component multicolor luminescence, particularly phosphorescence materials are highly attractive both in numerous applications and in-depth understanding the light-emission processes, but formidable challenges still exist for preparing such materials. Herein, a very facile approach is reported to synthesize carbon dots (CDs) (named MP-CDs) that exhibit multicolor fluorescence (FL), and more remarkably, multicolor long-lived room temperature phosphorescence (RTP) under ambient conditions. The FL and RTP colors of the CDs powder are observed to change from blue to green and cyan to yellow, respectively, with the excitation wavelength shifting from 254 to 420 nm. Further studies demonstrate that the multicolor emissions can be attributed to the existence of multiple emitting centers in the CDs and the relatively higher reaction temperature plays a critical role for achieving RTP. Given the unique optical properties, a preliminary application of MP-CDs in advanced anti-counterfeiting is presented. This study not only proposes a strategy to prepare photo-stimulated multicolor RTP materials, but also reveals great potentials of CDs in exploiting novel optical materials with unique properties.

Controllable Singlet-Triplet Energy Splitting of Graphene Quantum Dots through Oxidation: From Phosphorescence to TADF.

Long-lived afterglow emissions, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), are beneficial in the fields of displays, bioimaging, and data security. However, it is challenging to realize a single material that simultaneously exhibits both RTP and TADF properties with their relative strengths varied in a controlled manner. Herein, a new design approach is reported to control singlet-triplet energy splitting (∆EST ) in graphene quantum dots (GQD)/graphene oxide quantum dots (GOQDs) by varying the ratio of oxygenated carbon to sp2 carbon (γOC ). It is demonstrated that ∆EST decreases from 0.365 to 0.123 eV as γOC increases from 4.63% to 59.6%, which in turn induces a dramatic transition from RTP to TADF. Matrix-assisted stabilization of triplet excited states provides ultralong lifetimes to both RTP and TADF. Embedded in boron oxynitride, the low oxidized (4.63%) GQD exhibits an RTP lifetime (τT avg ) of 783 ms, and the highly oxidized (59.6%) GOQD exhibits a TADF lifetime (τDF avg ) of 125 ms. Furthermore, the long-lived RTP and TADF materials enable the first demonstration of anticounterfeiting and multilevel information security using GQD. These results will open up a new approach to the engineering of singlet-triplet splitting in GQD for controlled realization of smart multimodal afterglow materials.

New route to strong, long-lived room-temperature phosphorescence using organic phosphor guest-friendly matrices [Al(DMSO)6]X3 (X=Cl−, Br−)

Developing highly desirable organic compounds with strong long-lived room-temperature phosphorescence (RTP) under ambient conditions has been a grand challenge. Present here is a new type of crystalline matrices based on ionic solvento complexes, [Al(DMSO)6]X3 (X− = Cl−, Br−) which can trap various trace amount of organic phosphors to prepare low-cost RTP materials. The phosphorescence of such phases in the air at RT can demonstrate both long lifetime (up to 229.7 ms) and high quantum efficiency (up to 15.8%) due to RTP-enhancing X− anions and phosphor-protecting matrices. Further, the guest-friendly feature of the matrices enables the development of a multiple-RTP doped phase via the simultaneous inclusion of two phosphors into one matrix, enabling unprecedented two-dimensional anti-counterfeiting. The work not only finds a new and facile route to develop low-cost RTP materials including multiple-RTP materials but also expands their application domains.

Aggregation-Induced Room-Temperature Phosphorescence Obtained from Water-Dispersible Carbon Dot-Based Composite Materials.

Room-temperature phosphorescence (RTP) materials are desirable in chemical sensing because of their long emission lifetime and they are free from background autofluorescence. Nevertheless, the achievement of RTP in aqueous solution is still a highly challenging task. Herein, a molten salt method to prepare carbon dot (CD)-based RTP materials is presented by direct calcination of carbon sources in the presence of inorganic salts. The resultant CD composites (CDs@MP) exhibit bright RTP with a quantum yield of 26.4% and a lifetime of 1.28 s, which lasts for about 6 s to the naked eye. Importantly, their aqueous dispersion also has good RTP characteristics. This is the first time that the long-lived CDs@MP with RTP are achieved in aqueous solution owing to the synergistic effect of crystalline confinement and aggregation-induced phosphorescence. Further investigations reveal that three key processes may be responsible for the observed RTP of the composite materials: (1) The rigid crystalline salt shell can preserve the triplet states of CDs@MP in water and suppress the nonradiative deactivation; (2) The addition of high-charge-density metal ions Mg(II) and phosphorus element in the composite facilitates the singlet-to-triplet intersystem crossing process and enhances the RTP emission; (3) The aggregation of CDs@MP nanocomposites enables the matrix shell to self-assemble into a network, which further improves the rigidity of the shell and prevents the intermolecular motions, hence prolonging the RTP lifetime. The unique RTP feature and good water dispersibility allow the CD-based composite materials to be applicable in detection of temperature and pH in the aqueous phase. Our approach for producing long-lived RTP CDs@MP is effective, simple, and low-cost, which opens a new route to develop RTP materials that are applicable in aqueous solution.

Development of a Tethered Palladium–BODIPY Dual Catalyst for Enhanced Photo- and Thermally Activated Catalysis, and for Promoting Sequential Reactivity

In recent years there has been a growing interest in merging different types of catalysis to create new multistep catalytic processes. However, the majority of reported dual catalysis strategies use a mixture of individual catalysts, with limited reports of dual catalysis reactions where the different catalysts are combined in a single compound. This work reports the synthesis of a tethered palladium-BODIPY dual catalyst to enable increased synergistic interactions between the catalytic centres. Detailed analysis, including single crystal X-ray crystallography, absorption, fluorescence, and phosphorescence measurements, and kinetic analyses to determine singlet oxygen quantum yields, confirm that chemical tethering results in a significant increase in the photocatalytic potential of the palladium-BODIPY dual catalyst, relative to the parent BODIPY chromophore. Interestingly, the palladium-BODIPY complex also exhibited rare long-lived room temperature phosphorescence. Catalytic applications of the palladium-BODIPY dual catalyst indicate that chemical tethering increases the reactivity of the catalytic centres for both photocatalytic oxidation of thioanisole and palladium catalysed Suzuki–Miyaura cross coupling, highlighting that enhancements in both photo and thermally activated catalysis can be achieved on chemical tethering. In addition, the dual catalytic potential of the palladium-BODIPY catalyst was demonstrated using a representative sequential photocatalytic oxidation–cross coupling reaction.

Dense π-stacking of flexible ligands fixed in interpenetrating Zn(ii) MOF exhibiting long-lasting phosphorescence and efficient carrier transport.

Three-fold interpenetrating Zn(ii) MOF with the dense π-stacking of flexible ligands exhibit long-lived phosphorescence emission up to 91 ms at room temperature. Photoelectric measurements show efficient electro-hole separation based on the long lifetime of triplet state exciton.

Photosensitized long-lived room-temperature phosphorescence of naphthalene-d8 as a result of T–T energy transfer inside the 4′-tret-butylacetophonone- naphthalene-d8@2β-cyclodextrin inclusion complex

T–T energy transfer inside the supramolecular system has been performed resulting in photosensitized long-lived room-temperature phosphorescence of naphthalene-d8 included to the complex 4′-t-butylacetophenone–naphthalene-d8–2β-cyclodextrine (tBA⋅Nph-d8@2βCD). In this system, formed by self-assembly, the donor (D) of triplet energy was tBA, the acceptor (A) was naphthalene-d8. Upon deleting dissolved atmospheric oxygen with added sodium sulfite, the phosphorescence lifetime increased from 4.7 to 12.8 s. A mono-exponential character of decay curves was indicative of a uniform structure of the emitting species. Our quantum-chemical simulations have shown that, in the cavity of β-cyclodextrine dimer, D and A of triplet excitation are located closer (4.81 Å) than in free state (5.19 Å), which ensures efficient transfer of triplet excitation to naphthalene-d8.

The phosphorescence property of carbon dots presenting as powder, embedded in filter paper and dispersed in solid solution

Room temperature phosphorescence (RTP) has distinctive advantages over the fluorescence counterparts, such as larger Stokes shifts and longer lifetimes. It is challenging to design and prepare RTP carbon dots (CDs) because many of them need appropriate solid matrix or introducing heavy atoms for promoting intersystem crossing and suppressing vibrational dissipation between singlet and triplet states. In this paper, long-lived RTP carbon dots (EDA-CDs) were synthesized by microwave-assisted pyrolysis of ethylenediamine (EDA) in phosphoric acid solution. Interestingly, at room temperature, bright phosphorescence was observed for EDA-CDs embedded in filter paper and presenting as solid powder, and could last for 7 s to naked eyes, with the phosphorescence lifetime being up to 693.67 and 887.55 ms, respectively. At low temperature of 123 K, the phosphorescence lifetime of EDA-CDs in solid solution can reach the highest value of 1538 ms, while the phosphorescence lifetime of EDA-CDs presenting as solid powder is 1287.54 ms. It can be deduced that robust bridge-like hydrogen-bonded networks formed by highly ordered hydration water molecules around EDA-CDs in solid solution at low temperature are beneficial for rigidifying the surface groups of EDA-CDs and thus the longer phosphorescence lifetime. Finally, RTP EDA-CDs had shown a great potential to be as advanced security ink for information encryption and anti-counterfeiting.

Hydrogen Bonding-Induced Morphology Dependence of Long-Lived Organic Room-Temperature Phosphorescence: A Computational Study.

Organic room-temperature phosphorescence (RTP) is generally only exhibited in aggregate with strong dependence on morphology, which is highly sensitive to the intermolecular hydrogen bonding interaction. Here, 4,4'-bis(9H-carbazol-9-yl)methanone (Cz2BP), emitting RTP in a cocrystal consisting of chloroform but not in the amorphous nor in the crystal phase, was investigated to disclose the morphology dependence through molecular dynamics simulations and first-principles calculations. We find that the strong intermolecular C═O···H-C hydrogen bonds between Cz2BP and chloroform in cocrystals decrease the nonradiative decay rate of T1 → S0 by 3-6 orders of magnitude due to the vibronic decoupling effect on the C═O stretching motion and the increase of (π,π*) composition in the T1 state. The former is responsible for high efficiency and the latter for long-lived RTP with a calculated lifetime of 208 ms (exp. 353 ms). Nevertheless, the weak hydrogen bonds cannot cause any appreciable RTP in amorphous and crystal phases. This novel understanding opens a way to design organic RTP materials.