Ultralong room-temperature phosphorescence of a solid-state supramolecule between phenylmethylpyridinium and cucurbit[6]uril

Purely Organic Room-Temperature Phosphorescence Endowing Fast Intersystem Crossing from Through-Space Spin-Orbit Coupling

Purely organic room-temperature phosphorescence endowing very fast intersystem crossing from through-space systems has not been well investigated. Here we report three space-confined bridged phosphors, where phenothiazine is linked with dibenzothiophene, dibenzofuran, and carbazole by a 9,9-dimethylxanthene bridge. Nearly pure phosphorescence is observed in the crystals at room temperature. Interestingly, phosphorescence comes solely from the phenothiazine segment. Experimental results indicate that bridged counterparts of dibenzothiophene, dibenzofuran, and carbazole contribute as close-lying triplet states with locally excited (LE) character. The through-space spin-orbit coupling principle is proposed in these bridged systems, as their ¹LE and ³LE states have intrinsic spatial overlap, degenerate energy levels, and tilting face-to-face alignment. The resulting effective through-space spin-orbit coupling leads to efficient intersystem crossing a with rate constant as high as 10⁹ s^-1 and an overwhelming triplet decay channel of the singlet excited state.

Room-temperature phosphorescence of a water-soluble supramolecular organic framework

A flexible porous water-soluble supramolecular organic framework was developed, which could efficiently exhibit phosphorescence both in an aqueous phase and in a film state at room-temperature.

Polyacrylamide-Based Binary Luminescent Copolymer Materials Exhibit Color-Tunable and Efficient Long-Lived Room Temperature Phosphorescence

Polymer-based pure organic room temperature phosphorescence (RTP) materials have garnered considerable interest, among which RTP systems with prolonged lifetimes and tunable emission colors are promising for applications in sensing, flexible electronics, bioassay, anti-counterfeiting, and data encryption. Herein, facile doping method is reported based on two types of copolymers with benzene/biphenyl-based light-emitting cores as their side chains, whereby the two copolymers are robustly crosslinked via noncovalent interactions including hydrogen bonding and halogen bonding that occur between the light-emitting cores and polyacrylamide backbones. Persistent RTP emission with prolonged lifetime up to 1.9 s and phosphorescence quantum yield as high as 40.1% are obtained in single copolymers, attributed to the conformation restriction of phosphorescent dyes originating from the rigid microenvironment. Furthermore, multicolor phosphorescence signals are observed in the doped binary luminescent copolymer systems that can be effectively regulated by the feed ratio of luminescent cores and irradiation wavelengths. Possible mechanisms for this efficient and long-lived color-tunable RTP system are discussed on the basis of the experimental data and theoretical calculations. In addition, it is also demonstrated that the color-tunable RTP emission of the doped copolymer systems under ambient conditions allows for further exploitation in the application of dynamic information encryption.

Unexpected long room-temperature phosphorescence lifetimes of up to 1.0 s observed in iodinated molecular systems

We investigate the heavy atom effect on difluoroboron(iii) β-diketonate (BF₂bdk) luminescent compounds. The iodine-substituted BF₂bdk powders with 38 wt% iodine substituents show insignificant afterglow at 77 K. Unexpectedly, when doped into phenyl benzoate matrices, the iodine-substituted BF₂bdk exhibits bright room-temperature phosphorescence with lifetimes of up to 1.0 s under ambient conditions.

Supramolecular Purely Organic Room-Temperature Phosphorescence

In recent years, purely organic room-temperature phosphorescence (RTP) has aroused wide concern and promotes the development of the supramolecular phosphorescence. Different from organic crystallization, polymerization, or matrix rigidification, supramolecular strategy mainly takes advantage of the synergy between supramolecular co-assembly and strong binding by macrocyclic host compounds (cucurbit[n]urils, cyclodextrins, etc.) to overcome deficiencies such as poor processability and water solubility and improves RTP materials' quantum efficiency and lifetime in the solid state or in an aqueous solution. Meanwhile, it expands application, especially in aqueous solution, in cell imaging. Therefore, supramolecular phosphorescence will become a new growth point and will have broad application prospects in chemistry, biology, and material science.This Account focuses on the uniquely synergetic advantages of co-assembly and host-guest interaction from macrocyclic hosts for enhancing RTP. This Account starts with a brief introduction of the recent development of organic RTP materials as well as the host-guest interaction and co-assembly. Then, we introduce a supramolecular solid-state RTP strategy involving an ultrahigh phosphorescent quantum yield via the tight encapsulation of macrocyclic host cucurbit[6]uril, an ultralong lifetime via changing the substituents of phosphors, and long-lived and bright RTP by the synergy of host-guest interaction and polymerization. Meanwhile, the applications of solid-state RTP materials for anti-counterfeiting and data encryption are presented. The third part will be the water-phase supramolecular phosphorescence systems constructed by water-soluble macrocyclic host cucurbit[8]uril. Host-guest interaction and polymerization worked together toward efficient phosphorescence in aqueous solution, and the multi-stage assembly promoted phosphorescent applications such as cell targeted imaging and energy transfer. A humidity sensor and data encryption by the conversion of supramolecular hydrogels and xerogels are also involved. In the summary section, we present perspectives and possible research directions for supramolecular phosphorescence.Furthermore, on the basis of previous research, we would like to conclude and propose the developing concept of "macrocycles enhance guest's phosphorescence", and this concept not only means that the macrocyclic host limits the movement of the guest compound or promotes interactions between guest compounds but also involves the synergetic enhancement centered on macrocyclic compounds via multi-stage supramolecular assembly which further improves the efficiency of RTP, water solubility, and biocompatibility. And we believe that this concept will be able, together with theory of "assembly-induced emission" and "aggregation-induced emission", to accelerate the development of purely organic RTP materials.

Light-Harvesting Supramolecular Phosphors: Highly Efficient Room Temperature Phosphorescence in Solution and Hydrogels

Solution phase room-temperature phosphorescence (RTP) from organic phosphors is seldom realized. Herein we report one of the highest quantum yield solution state RTP (ca. 41.8 %) in water, from a structurally simple phthalimide phosphor, by employing an organic-inorganic supramolecular scaffolding strategy. We further use these supramolecular hybrid phosphors as a light-harvesting scaffold to achieve delayed fluorescence from orthogonally anchored Sulforhodamine acceptor dyes via an efficient triplet to singlet Förster resonance energy transfer (TS-FRET), which is rarely achieved in solution. Electrostatic cross-linking of the inorganic scaffold at higher concentrations further facilitates the formation of self-standing hydrogels with efficient RTP and energy-transfer mediated long-lived fluorescence.

TADF-Type Organic Afterglow

We report a highly efficient dopant-matrix afterglow system enabled by TADF mechanism to realize afterglow quantum yields of 60-70 %, which features a moderate rate constant for reverse intersystem crossing (k_RISC ) to simultaneously improve afterglow quantum yields and maintain afterglow emission lifetime. Difluoroboron β-diketonate (BF₂ bdk) compounds are designed with multiple electron-donating groups to possess moderate k_RISC values and are selected as luminescent dopants. The matrices with carbonyl functional groups such as phenyl benzoate (PhB) have been found to interact with and perturb BF₂ bdk excited states by dipole-dipole interactions and thus enhance the intersystem crossing of BF₂ bdk excited states. Through dopant-matrix collaboration, the efficient TADF-type afterglow materials have been achieved to exhibit excellent processability into desired shapes and large-area films by melt casting, as well as aqueous afterglow dispersions for potential bioimaging applications.

Cucurbituril Based Luminescent Materials in Aqueous Media and Solid State

Cucurbit[n]urils, the pumpkin shaped macrocyclic host molecules possessing a hydrophobic cavity and two identical carbonyl portals, have drawn a lot of attention in recent years due to their high-affinity yet dynamic molecular recognition properties in water. The reversible and stimuli-responsive nature of their host-guest complexes imparts "smart" features leading to materials with intriguing optical, mechanical and morphological properties. In this review, we focus on the design of cucurbituril based luminescent materials in aqueous media as well in solid or film state. The design principles of fluorescent complexes, small assemblies as well as supramolecular polymers along with their stimuli-responsive properties and applications in diverse areas such as optoelectronic devices, light harvesting, anti-counterfeiting and information technology, cell imaging, etc are highlighted with selected examples from recent literature. We also discuss examples of room temperature phosphorescent materials derived from purely organic luminogens in the presence of cucurbiturils.

Wide-range lifetime-tunable and responsive ultralong organic phosphorescent multi-host/guest system

The rational lifetime-tuning strategy of ultralong organic phosphorescence is extraordinarily important but seldom reported. Herein, a series of multi-host/guest ultralong organic phosphorescence materials with dynamic lifetime-tuning properties were reported. By doping a non-room-temperature phosphorescence emitter into various solid host matrices with continuously reduced triplet energy levels, a wide-range lifetime (from 3.9 ms gradually to 376.9 ms) phosphorescence with unchangeable afterglow colors were realized. Further studies revealed that the host matrices were employed to afford rigid environment and proper energy levels to generate and stabilize the long-live triplet excitons. Meanwhile, these multi-host/guest ultralong organic phosphorescence materials also exhibited excitation-dependent phosphorescence and temperature-controlled afterglow on/off switching properties, according to the virtue of various photophysical and thermal properties of the host matrices. This work provides a guiding strategy to realize lifetime-tuning ultralong organic phosphorescence with lifetime-order encoding characteristic towards widespread applications in time-resolved information displaying, higher-level security protection, and dynamic multi-dimensional anti-counterfeiting.

Modulating Charge Separation and Intersystem Crossing in Donor-Switch-Acceptor Systems: A Computational Study

Charge separation and intersystem crossing play critical roles in various applications of organic long persistent luminescence materials, including light-emitting diodes, chemical sensors, theranostics, and many biomedical and information applications. Using first-principles calculations, we demonstrate that an azobenzene acting as a photoswitch can be used for altering the configuration of a donor-switch-acceptor (D-S-A) molecular system to ensure charge separation and promote intersystem crossing upon photoexcitation. The trans to cis photoisomerization of an azobenzene switch creates an electron trap that stabilizes the charge-separated state. The cis conformation further facilitates the singlet to triplet intersystem crossing in the excited state. Our theoretical study of the D-S-A system may help the design of long persistent luminescent organic devices.

Supramolecular Pins with Ultralong Efficient Phosphorescence

Constructing ultralong organic phosphorescent materials possessing a high quantum yield is challenging. Herein, assemblies of purely organic supramolecular pins composed of alkyl-bridged phenylpyridinium salts and cucurbit[8]uril (CB[8]) are reported. Different from "one host with two guests" and "head-to-tail" binding, the binding formation of supramolecular pins is "one host with one guest" and "head-to-head," which overcomes electrostatic repulsion and promotes intramolecular charge transfer. The supramolecular pin 1/CB[8] displays afterglow with high phosphorescence quantum yield (99.38%) after incorporation into a rigid matrix, which is the highest yield reported to date for phosphorescent materials. Moreover, multicolor photoluminescence can be obtained by different excitation wavelengths and ratios of host to guest. Owing to the redshift of the absorption, the supramolecular pins are applied for targeted phosphorescence imaging of mitochondria. This work will provide a reasonable supramolecular strategy to achieve redshifted and efficient phosphorescence both in the solid state and in aqueous solution.

Boosting Wide-Range Tunable Long-Afterglow in 1D Metal-Organic Halide Micro/Nanocrystals for Space/Time-Resolved Information Photonics

Molecular afterglow materials with ultralong-lived excited states have attracted considerable interest owing to their promise for light-emitting devices, optical imaging, and anti-counterfeiting applications. However, the realization of ultralong afterglow emission in low-dimensional micro/nanostructures has remained an open challenge, limiting progress toward new-generation photonic applications. In this work, new types of mono/binuclear metal-organic halide micro/nanocrystals with tunable afterglow properties, made possibly by the rational control over both ultralong-lived room-temperature phosphorescence and thermally activated delayed fluorescence, are developed. Interestingly, the mono/binuclear coordination complexes present excitation-dependent luminescence across a wide range (wavelength > 150 nm) with broad emission color differences from blue to yellow owing to the multiple long-lived excited states. The 1D binuclear metal-organic microrods further exhibit excitation-dependent optical waveguide and space/time dual-resolved afterglow emission properties, endowing them with great potential in wavelength-division multiplexing information photonics and logic gates. Therefore, this work not only communicates the first example of wide-range tunable ultralong afterglow of low-dimensional metal-organic micro/nanocrystals under ambient conditions but also provides a new route to achieve optical communications and photonic logic compilation at the micro/nanoscale.

Recent advances in persistent luminescence based on molecular hybrid materials

Molecular persistently luminescent materials have received recent attention due to their promising applications in optical displays, biological imaging, chemical sensing, and security systems. In this review, we systematically summarize recent advances in establishing persistently luminescent materials-specifically focusing on materials composed of molecular hybrids for the first time. We describe the main strategies for synthesizing these hybrid materials, namely: (i) inorganics/organics, (ii) organics/organics, and (iii) organics/polymer systems and demonstrate how molecular hybrids provide synergistic effects, while improving luminescence lifetimes and efficiencies. These hybrid materials promote new methods for tuning key physical properties such as singlet-triplet excited state energies by controlling the chemical interactions and molecular orientations in the solid state. We review new advances in these materials from the perspective of examining experimental and theoretical approaches to room-temperature phosphorescence and thermally-activated delayed fluorescence. Finally, this review concludes by summarizing the current challenges and future opportunities for these hybrid materials.

Efficient metal-free organic room temperature phosphors

An innovative transformation of organic luminescent materials in recent years has realised the exciting research area of ultralong room-temperature phosphorescence. Here the credit for the advancements goes to the rational design of new organic phosphors. The continuous effort in the area has yielded wide varieties of metal-free organic systems capable of extending the lifetime to several seconds under ambient conditions with high quantum yield and attractive afterglow properties. The various strategies adopted in the past decade to manipulate the fate of triplet excitons suggest a bright future for this class of materials. To analyze the underlying processes in detail, we have chosen high performing organic triplet emitters that utilized the best possible ways to achieve a lifetime above one second along with impressive quantum yield and afterglow properties. Such a case study describing different classes of metal-free organic phosphors and strategies adopted for the efficient management of triplet excitons will stimulate the development of better candidates for futuristic applications. This Perspective discusses the phosphorescence features of single- and multi-component crystalline assemblies, host-guest assemblies, polymers, and polymer-based systems under various classes of molecules. The various applications of the organic phosphors, along with future perspectives, are also highlighted.

Multidimensional Information Encryption and Storage: When the Input Is Light

The issue of information security is closely related to every aspect of daily life. For pursuing a higher level of security, much effort has been continuously invested in the development of information security technologies based on encryption and storage. Current approaches using single-dimension information can be easily cracked and imitated due to the lack of sufficient security. Multidimensional information encryption and storage are an effective way to increase the security level and can protect it from counterfeiting and illegal decryption. Since light has rich dimensions (wavelength, duration, phase, polarization, depth, and power) and synergy between different dimensions, light as the input is one of the promising candidates for improving the level of information security. In this review, based on six different dimensional features of the input light, we mainly summarize the implementation methods of multidimensional information encryption and storage including material preparation and response mechanisms. In addition, the challenges and future prospects of these information security systems are discussed.

Guest-boosted phosphorescence efficiency of a supramolecular cage

The quantum yield and emission lifetime of the inclusion complexes can be fine-tuned via the variation of halobenzene guests.

A twin-axial pseudorotaxane for phosphorescence cell imaging

A twin-axial pseudorotaxane is constructed using a phenylpyridine salt with diethanolamine (DA-PY) and cucurbit[8]uril (CB[8]), and it not only displays phosphorescence in aqueous solution but it can also be used for targeted cell-imaging.

Purely organic light-harvesting phosphorescence energy transfer by β-cyclodextrin pseudorotaxane for mitochondria targeted imaging

A new type of purely organic light-harvesting phosphorescence energy transfer (PET) supramolecular assembly is constructed from 4-(4-bromophenyl)-pyridine modified β-cyclodextrin (CD-PY) as a donor, cucurbit[8]uril (CB[8]) as a mediator, rhodamine B (RhB) as an acceptor, and adamantane modified hyaluronic acid (HA-ADA) as a cancer cell targeting agent. Interestingly, the complexation of free CD-PY, which has no RTP emission in aqueous solution, with CB[8] results in the formation of CD-PY@CB[8] pseudorotaxane with an RTP emission at 510 nm. Then the addition of RhB leads to an efficient light-harvesting PET process with highly efficient energy transfer and an ultrahigh antenna effect (36.42) between CD-PY@CB[8] pseudorotaxane and RhB. Importantly, CD-PY@CB[8]@RhB assembles with HA-ADA into nanoparticles with further enhanced delayed emission at 590 nm. The nanoparticles could be successfully used for mitochondria targeted imaging in A549 cancer cells. This aqueous-state PET based on a supramolecular assembly strategy has potential application in delayed fluorescence cell imaging.

A new type of purely organic light-harvesting PET supramolecular assembly is constructed with efficient energy transfer and ultrahigh antenna effect. Moreover, the assembly could be used for mitochondria targeted imaging in A549 cancer cells.

Ultralong purely organic aqueous phosphorescence supramolecular polymer for targeted tumor cell imaging

Purely organic room-temperature phosphorescence has attracted attention for bioimaging but can be quenched in aqueous systems. Here we report a water-soluble ultralong organic room-temperature phosphorescent supramolecular polymer by combining cucurbit[n]uril (CB[7], CB[8]) and hyaluronic acid (HA) as a tumor-targeting ligand conjugated to a 4-(4-bromophenyl)pyridin-1-ium bromide (BrBP) phosphor. The result shows that CB[7] mediated pseudorotaxane polymer CB[7]/HA-BrBP changes from small spherical aggregates to a linear array, whereas complexation with CB[8] results in biaxial pseudorotaxane polymer CB[8]/HA-BrBP which transforms to relatively large aggregates. Owing to the more stable 1:2 inclusion complex between CB[8] and BrBP and the multiple hydrogen bonds, this supramolecular polymer has ultralong purely organic RTP lifetime in water up to 4.33 ms with a quantum yield of 7.58%. Benefiting from the targeting property of HA, this supramolecular polymer is successfully applied for cancer cell targeted phosphorescence imaging of mitochondria.

Wide-Range Color-Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks

Organic materials with long-lived, color-tunable phosphorescence are potentially useful for optical recording, anti-counterfeiting, and bioimaging. Herein, we develop a series of novel host-guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra-long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color-tunable inks have already been developed using visible dyes, solution-processed security inks that are temperature dependent and display time-resolved printed images are unprecedented. This strategy can provide a crucial step towards the next-generation of security technologies for information handling.

Aromatic Phosphonates: A Novel Group of Emitters Showing Blue Ultralong Room Temperature Phosphorescence

In recent years, there has been a growing interest in purely organic materials showing ultralong room-temperature phosphorescence with lifetimes in the range of seconds. Still, the longest known phosphorescence lifetimes are only achieved with crystalline systems so far. Here, a rational design of a completely new family of halogen-free organic luminescent derivatives in amorphous matrices, displaying both conventional fluorescence and phosphorescence is reported. Hydrogen bonding between the newly developed emitters and an ethylene-vinyl alcohol copolymer (Exceval) matrix, which efficiently suppresses vibrational dissipation, enables bright long-lived phosphorescence with lifetimes up to 2.6 s at around 480 nm. The importance of the chosen matrix is shown as well as the implementation in an organic programmable luminescent tag.

Heat-resistant Pb(ii)-based X-ray scintillating metal–organic frameworks for sensitive dosage detection via an aggregation-induced luminescent chromophore

Unusual X-aggregation induced luminescent chromophores in heat-resistant Pb(ii)-based metal–organic frameworks facilitate excellent scintillation for X-ray dosage detection.

Tunable room temperature phosphorescence and energy transfer in ratiometric co-crystals

Color-tunable green and yellow room temperature phosphorescence is realized through a ratiometric co-crystal strategy.