Abnormal thermally-stimulated dynamic organic phosphorescence.

Dynamic luminescence behavior by external stimuli, such as light, thermal field, electricity, mechanical force, etc., endows the materials with great promise in optoelectronic applications. Upon thermal stimulus, the emission is inevitably quenched due to intensive non-radiative transition, especially for phosphorescence at high temperature. Herein, we report an abnormal thermally-stimulated phosphorescence behavior in a series of organic phosphors. As temperature changes from 198 to 343 K, the phosphorescence at around 479 nm gradually enhances for the model phosphor, of which the phosphorescent colors are tuned from yellow to cyan-blue. Furthermore, we demonstrate the potential applications of such dynamic emission for smart dyes and colorful afterglow displays. Our results would initiate the exploration of dynamic high-temperature phosphorescence for applications in smart optoelectronics. This finding not only contributes to an in-depth understanding of the thermally-stimulated phosphorescence, but also paves the way toward the development of smart materials for applications in optoelectronics.

Achieving High-Temperature Phosphorescence by Organic Cocrystal Engineering.

Organic phosphors offer a promising alternative in optoelectronics, but their temperature-sensitive feature has restricted their applications in high-temperature scenarios, and the attainment of high-temperature phosphorescence (HTP) is still challenging. Herein, a series of organic cocrystal phosphors are constructed by supramolecular assembly with an ultralong emission lifetime of up to 2.16 s. Intriguingly, remarkable stabilization of triplet excitons can also be realized at elevated temperature, and green phosphorescence is still exhibited in solid state even up to 150 °C. From special molecular packing within the crystal lattice, it has been observed that the orientation of isolated water cluster and well-controlled molecular organization via multiple interactions can favor the structural rigidity of cocrystals more effectively to suppress the nonradiative transition, thus resulting in efficient room-temperature phosphorescence and unprecedented survival of HTP.

Organic Excitonic State Management by Surface Metallic Coupling of Inorganic Lanthanide Nanocrystals.

The ability to harness charges and spins for control of organic excitonic states is critical in developing high-performance organic luminophores and optoelectronic devices. Here we report a facile strategy to efficiently manipulate the electronic energy states of various organic phosphors by coupling them with inorganic lanthanide nanocrystals. We show that the metallic atoms exposed on the nanocrystal surface can introduce strong coupling effects to 9-(4-ethoxy-6-phenyl-1,3,5-triazin-2-yl)-9H-carbazole (OCzT) and some organic chromophores with carbazole functional groups when the organics are approaching the nanocrystals. This unconventional organic-inorganic hybridization enables a nearly 100 % conversion of the singlet excitation to fast charge transfer luminescence that does not exist in pristine organics, which broadens the utility of organic phosphors in hybrid systems.

Regulating Isolated-Molecular and Aggregated-State Phosphorescence for Multicolor Afterglow by Photoactivation.

Ultralong organic phosphorescence (UOP) materials have attracted considerable attention in recent years. Herein, a new type of flexible films is fabricated by doping amphipathic pyrene tetrasulfonic acid sodium salts into amorphous poly(vinyl alcohol) matrix, which enables the realization of color-tunable UOP spanning from orange-red to green after excitation light is switched off. Interestingly, precise control of the proportion of isolated-molecular and aggregated-state phosphorescence is demonstrated for colorful afterglow using photo-activation. An increase in the dynamic phosphorescence lifetime of isolated molecules is observed from 894.75 to 1735.71 ms following an 8 min irradiation under ambient conditions. The photo-activation, however, showed little influence on aggreated-state phosphorescence. This flexible and processable film exhibits versatile applications in multicolor afterglow displays, ultraviolet detection, multilevel information encryption, etc. This study not only provides a strategy for the rational regulation of UOP colors but also expands the application potential of color-tunable UOP materials.

Ultralong Organic Phosphorescence: From Material Design to Applications.

Organic phosphorescence is defined as a radiative transition between the different spin multiplicities of an organic molecule after excitation; here, we refer to the photoexcitation. Unlike fluorescence, it shows a long emission lifetime (∼µs), large Stokes shift, and rich excited state properties, attracting considerable attention in organic electronics during the past years. Ultralong organic phosphorescence (UOP), a type of persistent luminescence in organic phosphors, shows an emission lifetime of over 100 ms normally according to the resolution limit of the naked eye. According to the Jablonski energy diagram, two prerequisites are necessary for UOP generation and enhancement. One is to promote intersystem crossing (ISC) of the excitons from the excited singlet to triplet states by enhancing the spin-orbit coupling (SOC); the other is to suppress the nonradiative transitions of the excitons from the excited triplet states.In this Account, we will give a summary of our research on ultralong organic phosphorescence, including the design of materials, manipulation of properties, fabrication of nano/microstructures, and function applications. First, we give a brief introduction to the UOP development. Then, we discuss the constructed methods of UOP materials from the inter/intramolecular interaction types, including π-π interactions, intermolecular hydrogen bonds, halogen bonds, ionic bonds, covalent bonds, and so on. These effective interactions can build a rigid environment to restrain the nonradiative transitions from the molecular motions or external quenching by oxygen, moisture, or heat, and thus enhance the UOP performance. Next, the manipulation of UOP properties, containing excitation wavelength, emission colors, lifetimes, and quantum efficiency (QE), through molecular or crystal engineering will be summarized. Recently, the excitation wavelengths of the materials for UOP can be regulated in different regions, such as UV, visible light, and X-ray; the emission colors of UOP can cover the whole visible-light region, from deep blue to red; the phosphorescence lifetime of UOP materials can reach 2.5 s, and the quantum efficiency can be achieved up to 96.5%. Moreover, we will present the fabrication of micro/nanoscale UOP materials, including the preparation of micro/nanostructure, optical performance, and device fabrication. Afterward, we will review the potential applications of UOP materials in organic/bio-optoelectronics, such as information encryption, bioimaging, sensing, afterglow display, etc. Finally, an outlook on the development of UOP materials and applications will be proposed.

Structural materials with afterglow room temperature phosphorescence activated by lignin oxidation.

Sustainable afterglow room temperature phosphorescence (RTP) materials, especially afterglow RTP structural materials, are crucial but remain difficult to achieve. Here, an oxidation strategy is developed to convert lignin to afterglow materials with a lifetime of ~ 408 ms. Specifically, lignin is oxidized to give aromatic chromophores and fatty acids using H2O2. The aromatic chromophores are locked by a fatty acid-based matrix by hydrogen bonds, triggering enhanced spin orbit coupling and long afterglow emission. More interestingly, motivated by this discovery, an auto fabrication line is built to convert wood (natural structural materials) to wood with afterglow RTP emission (RTP wood) via in situ oxidation of naturally-occurring lignin located in the wood cell walls to oxidized lignin (OL). The as-prepared RTP wood exhibits great potential for the construction of sustainable afterglow furniture. With this research we provide a new strategy to promote the sustainability of afterglow RTP materials and structural materials.

Ultralong organic phosphorescence from isolated molecules with repulsive interactions for multifunctional applications.

Intermolecular interactions, including attractive and repulsive interactions, play a vital role in manipulating functionalization of the materials from micro to macro dimensions. Despite great success in generation of ultralong organic phosphorescence (UOP) by suppressing non-radiative transitions through attractive interactions recently, there is still no consideration of repulsive interactions on UOP. Herein, we proposed a feasible approach by introducing carboxyl groups into organic phosphors, enabling formation of the intense repulsive interactions between the isolated molecules and the matrix in rigid environment. Our experimental results show a phosphor with a record lifetime and quantum efficiency up to 3.16 s and 50.0% simultaneously in film under ambient conditions. Considering the multiple functions of the flexible films, the potential applications in anti-counterfeiting, afterglow display and visual frequency indicators were demonstrated. This finding not only outlines a fundamental principle to achieve bright organic phosphorescence in film, but also expands the potential applications of UOP materials.

Endowing matrix-free carbon dots with color-tunable ultralong phosphorescence by self-doping.

Color-tunable ultralong phosphorescence is urgently desired in optoelectronic applications. Herein, we report a new type of full-color-tunable ultralong phosphorescence carbon dots (CDs) without matrix-assistance by a self-doping method under ambient conditions. The phosphorescence color can be rationally tuned from blue to red by changing the excitation wavelength from 310 to 440 nm. The CDs exhibit an ultralong lifetime of up to 1052.23 ms at 484 nm. From the experimental data, we speculate that the excitation-dependent multi-color phosphorescence is attributed to the presence of multiple emitting centers related to carbonyl units. Given the unique color-tunability of CDs, we demonstrate their potential applications in information encryption, light detection ranging from UV to visible light and LED devices. This finding not only takes a step towards the fundamental design of full-color emissive materials, but also provides a broader scope for the applications of phosphorescent materials.

Highly Efficient Blue Phosphorescence from Pillar-Layer MOFs by Ligand Functionalization.

Room temperature phosphorescence (RTP) has been extensively researched in heavy-metal containing complexes and purely organic systems. Despite the rapid blossom of RTP materials, it is still a tremendous challenge to develop highly efficient blue RTP materials with long-lived lifetimes. Taking the metal-organic framework (MOF) as a model, herein, a feasible strategy of ligand functionalization is proposed, including two essential elements, to develop blue phosphorescence materials with high efficiency and long-lived lifetimes simultaneously under ambient conditions. One is isolation of the chromophores with assistance of another predefined co-ligands, the other is restriction of the chromophores' motions through coordination and host-guest interactions. Remarkably, it renders the MOFs with highly efficient blue phosphorescence up to 80.6% and a lifetime of 169.7 ms under ambient conditions. Moreover, a demo of the crown is fabricated with MOFs ink by 3D printing technique. The potential applications for anti-counterfeiting and fingerprint visualization have been also demonstrated. This finding not only outlines a universal principle to design and synthesize highly efficient RTP materials, but also endows traditional MOFs with fresh vitality for potential applications.

Circularly Polarized Organic Room Temperature Phosphorescence from Amorphous Copolymers.

Organic optoelectronic functional materials featuring circularly polarized emission and persistent luminescence represent a novel research frontier and show promising applications in data encryption, displays, biological imaging, and so on. Herein, we present a simple and universal approach to achieve circularly polarized organic phosphorescence (CPP) from amorphous copolymers by the incorporation of axial chiral chromophores into polymer chains via radical cross-linked polymerization. Our experimental data reveal that copolymers (R/S)-PBNA exhibit a maximum CPP efficiency of 30.6% and the largest dissymmetric factor of 9.4 × 10-3 and copolymers (R/S)-PNA show the longest lifetime of 0.68 s under ambient conditions. Given the CPP property of these copolymers, their potential applications in multiple information encryption and displays are demonstrated, respectively. These findings not only lay the foundation for the development of amorphous polymers with superior CPP but also expand the outlook of room-temperature phosphorescent materials.

Confining isolated chromophores for highly efficient blue phosphorescence.

High-efficiency blue phosphorescence emission is essential for organic optoelectronic applications. However, synthesizing heavy-atom-free organic systems having high triplet energy levels and suppressed non-radiative transitions-key requirements for efficient blue phosphorescence-has proved difficult. Here we demonstrate a simple chemical strategy for achieving high-performance blue phosphors, based on confining isolated chromophores in ionic crystals. Formation of high-density ionic bonds between the cations of ionic crystals and the carboxylic acid groups of the chromophores leads to a segregated molecular arrangement with negligible inter-chromophore interactions. We show that tunable phosphorescence from blue to deep blue with a maximum phosphorescence efficiency of 96.5% can be achieved by varying the charged chromophores and their counterions. Moreover, these phosphorescent materials enable rapid, high-throughput data encryption, fingerprint identification and afterglow display. This work will facilitate the design of high-efficiency blue organic phosphors and extend the domain of organic phosphorescence to new applications.

Tunable microstructures of ultralong organic phosphorescence materials.

Three kinds of microstructures were prepared for one organic phosphor based on a solution-concentration-controlled self-assembly strategy. These microstructures show different phosphorescence efficiencies, which holds considerable promise for the miniaturized optical device applications of ultralong organic phosphorescence materials.

Color-tunable ultralong organic room temperature phosphorescence from a multicomponent copolymer.

Functional materials displaying tunable emission and long-lived luminescence have recently emerged as a powerful tool for applications in information encryption, organic electronics and bioelectronics. Herein, we present a design strategy to achieve color-tunable ultralong organic room temperature phosphorescence (UOP) in polymers through radical multicomponent cross-linked copolymerization. Our experiments reveal that by changing the excitation wavelength from 254 to 370 nm, these polymers display multicolor luminescence spanning from blue to yellow with a long-lived lifetime of 1.2 s and a maximum phosphorescence quantum yield of 37.5% under ambient conditions. Moreover, we explore the application of these polymers in multilevel information encryption based on the color-tunable UOP property. This strategy paves the way for the development of multicolor bio-labels and smart luminescent materials with long-lived emission at room temperature.

Amorphous Ionic Polymers with Color-Tunable Ultralong Organic Phosphorescence.

Amorphous purely organic phosphorescence materials with long-lived and color-tunable emission are rare. Herein, we report a concise chemical ionization strategy to endow conventional poly(4-vinylpyridine) (PVP) derivatives with ultralong organic phosphorescence (UOP) under ambient conditions. After the ionization of 1,4-butanesultone, the resulting PVP-S phosphor showed a UOP lifetime of 578.36 ms, which is 525 times longer than that of PVP polymer itself. Remarkably, multicolor UOP emission ranging from blue to red was observed with variation of the excitation wavelength, which has rarely been reported for organic luminescent materials. This finding not only provides a guideline for developing amorphous polymers with UOP properties, but also extends the scope of room-temperature phosphorescence (RTP) materials for practical applications in photoelectric fields.

Enabling long-lived organic room temperature phosphorescence in polymers by subunit interlocking.

Long-lived room temperature phosphorescence (LRTP) is an attractive optical phenomenon in organic electronics and photonics. Despite the rapid advance, it is still a formidable challenge to explore a universal approach to obtain LRTP in amorphous polymers. Based on the traditional polyethylene derivatives, we herein present a facile and concise chemical strategy to achieve ultralong phosphorescence in polymers by ionic bonding cross-linking. Impressively, a record LRTP lifetime of up to 2.1 s in amorphous polymers under ambient conditions is set up. Moreover, multicolor long-lived phosphorescent emission can be procured by tuning the excitation wavelength in single-component polymer materials. These results outline a fundamental principle for the construction of polymer materials with LRTP, endowing traditional polymers with fresh features for potential applications.

Room-Temperature Phosphorescence from Metal-Free Organic Materials in Solution: Origin and Molecular Design.

Metal-free organic materials with room-temperature phosphorescence (RTP) is hardly achieved in solution owing to the ambiguous underlying mechanism. By combining thermal vibration correlation function rate theory and a polarizable continuum model (PCM) coupled with the Tamm-Dancoff approximation method, concentrating on ß-hydroxyvinylimine boron compounds C-BF2 and S-BF2, we showed that the increased intersystem crossing ( kisc) and radiative decay rates ( kp) are responsible for the strong RTP of S-BF2 in solution. From C-BF2 to S-BF2, the T2 state is increasingly dominated by the n → π* transition, largely enhancing the kisc of S1 → T2 (up to 3 orders of magnitude) and kp of T1 → S0. Impressively, the nonradiative decay rate of T1 → S0 is slightly increased by suppressing the out-of-plane twisting motions. This mechanism is also tenable for several designed RTP molecules through further experimental demonstration, which will pave a new way to design organic materials with single-molecule phosphorescence for applying to organic light-emitting diodes.

Highly Efficient Ultralong Organic Phosphorescence through Intramolecular-Space Heavy-Atom Effect.

Metal-free organic phosphorescent materials have attracted considerable attention in the fields of organic electronics and bioelectronics. However, it remains a great challenge to achieve organic phosphors with high quantum efficiency in a single-component system. We designed and synthesized two organic phosphors (PDCz and PDBCz) with an ultralong organic phosphorescence (UOP) feature. Both molecules showed ultralong emission lifetime of >200 ms. For PDBCz crystal, it was found that the absolute phosphorescence quantum efficiency reaches up to 38.1%. Combining the experimental and theoretical studies, the highly efficient UOP was mainly attributed to the intramolecular space heavy-metal effect, which facilitates the spin-orbit coupling between singlet and triplet excited states to effectively promote the intersystem crossing. This study will provide a new platform to rationally design highly efficient UOP materials and show its potential in the field of flexible electronics.

Colour-tunable ultralong organic phosphorescence upon temperature stimulus.

A new class of single-component molecular crystal with colour-tunable ultralong organic phosphorescence (UOP) was designed and synthesized through alkyl chain engineering. Forming a more rigid environment at 77 K, the colour-tunable UOP from yellow-white to blue-green is achieved through dual-emission of crystal and amorphous states.