Achieving Ultralong Room-Temperature Phosphorescence in Covalent Organic Framework System.

The combination of room-temperature phosphorescence (RTP) and covalent organic frameworks (COFs) would give rise to a new class of functional materials with sensing and responsive properties. However, such organic materials have been rarely reported, especially for those with long phosphorescence lifetimes. Here we report the incorporation of RTP emitters into COFs either via chemical decoration or noncovalent doping to achieve ultralong RTP in a COF system. The RTP emitters are designed with small phosphorescence rates and consequently exhibit ultralong phosphorescence lifetimes when nonradiative decay and oxygen quenching are suppressed in COF system. The RTP-COF materials have been found to possess oxygen sensing properties with large response of phosphorescence lifetimes.

Achieving Visible-Light-Excitable Blue TADF-Type Afterglow via Delicate Control of Excited States in Difluoroboron ß-Diketonate Systems.

Blue afterglow constitutes of one of the primary afterglow colors and can convert into other afterglow colors through energy transfer. The reported studies show the fabrication of blue afterglow emitters, but most of them are formed by room-temperature phosphorescence mechanism and require UVB lights as excitation source (these high-energy lights may damage organic systems). Here we report visible-light-excitable blue thermally activated delayed fluorescence type (TADF-type) afterglow materials via delicate control of excited states in difluoroboron ß-diketonate (BF2bdk) systems. Tiny change of the substituents in BF2bdk system has been found to pose significant influence on excited state energy levels and consequently narrow the singlet-triplet splitting energy of the system. As a result, both forward and reverse intersystem crossing have been accelerated, leading to the emergence of BF2bdk's TADF-type organic afterglow in rigid crystalline matrices. The resultant TADF-type afterglow materials exhibit emission lifetimes of several hundred milliseconds, photoluminescence quantum yield (PLQY) of 24.7 % and display temperature responsive property.

Dopant-Matrix Afterglow Systems: Manipulation of Room-Temperature Phosphorescence/Thermally Activated Delayed Fluorescence Afterglow Mechanism via Mismatch/Match of Intermolecular Charge Transfer between Dopants and Matrices.

Dopant-matrix organic afterglow materials exhibit ease of fabrication and intriguing functions in diverse fields. However, a deep and comprehensive understanding of their photophysical behaviors remains elusive. Here we report manipulation of a room-temperature phosphorescence/thermally activated delayed fluorescence (RTP/TADF) afterglow mechanism via the mismatch/match of intermolecular charge transfer between dopants and matrices. When dispersed in inert crystalline matrices, the luminescent dopants show RTP lifetimes up to 2 s. Interestingly, when suitable organic matrices are selected, the resultant dopant-matrix materials display a TADF-type afterglow under ambient conditions due to the formation of dopant-matrix intermolecular charge transfer complexes. Detailed studies reveal that reverse intersystem crossing from dopants' T1 states to charge transfer complexes' S1 states, which features a moderate kRISC of 101-102 s-1, is responsible for the emergence of a TADF-type organic afterglow in rigid crystalline matrices. Such less reported delicate photophysics reveals a new aspect of the excited state property in dopant-matrix afterglow systems.

A narrow-band deep-blue MRTADF-type organic afterglow emitter.

We report a multi-resonant thermally activated delayed fluorescent (MRTADF) afterglow emitter with unprecedented long emission lifetime > 100 ms, full-width at half-maximum < 40 nm, and deep-blue emission color of CIEy at 0.048. Such emitters remain rarely achieved and would show potential applications in multiplexed bioimaging and high-density information encryption.

Visible-light-excitable aqueous afterglow exhibiting long emission wavelength and ultralong afterglow lifetime of 7.64 s.

We utilize the dopant-matrix strategy and emulsion polymerization to obtain aqueous afterglow dispersions from a liquid precursor, which avoids the processing of solid materials, protects organic triplets and achieves long phosphorescence lifetime of 7.64 s. The aqueous afterglow dispersions display great potential for biomedical applications due to their ultralong-lived excited states.

Mechanism landscape in pyrylium induced organic afterglow systems.

Manipulation of excited states and their dynamics represents a central topic in luminescence systems. We report an unexpected emergence of a high-performance organic afterglow in pyrylium induced photopolymerization systems, as well as the establishment of the mechanism landscape of the afterglow systems as a function of monomer types. In the case of methyl methacrylate, after pyrylium-catalyzed photopolymerization, the obtained materials exhibit a TADF-type organic afterglow with an afterglow efficiency of 70.4%. By using heavy-atom-containing methacrylate, the external heavy atom effect speeds up phosphorescence decay and switches on room-temperature phosphorescence in pyrylium-polymer systems. When 9-vinylcarbazole is used, the resultant materials display organic long persistent luminescence with hour-long durations and emission maxima around 650 nm. The intriguing mechanism landscape reflects the delicate balance of multiple photophysical processes in the pyrylium induced organic afterglow systems, which has been rarely explored in the reported studies.

A direct observation of up-converted room-temperature phosphorescence in an anti-Kasha dopant-matrix system.

It is common sense that emission maxima of phosphorescence spectra (λP) are longer than those of fluorescence spectra (λF). Here we report a serendipitous finding of up-converted room-temperature phosphorescence (RTP) with λP < λF and phosphorescence lifetime > 0.1 s upon doping benzophenone-containing difluoroboron ß-diketonate (BPBF2) into phenyl benzoate matrices. The up-converted RTP is originated from BPBF2's Tn (n ≥ 2) states which show typical 3n-π* characters from benzophenone moieties. Detailed studies reveal that, upon intersystem crossing from BPBF2's S1 states of charge transfer characters, the resultant T1 and Tn states build T1-to-Tn equilibrium. Because of their 3n-π* characters, the Tn states possess large phosphorescence rates that can strongly compete RTP(T1) to directly emit RTP(Tn) which violates Kasha's rule. The direct observation of up-converted RTP provides deep understanding of triplet excited state dynamics and opens an intriguing pathway to devise visible-light-excitable deep-blue afterglow emitters, as well as stimuli-responsive afterglow materials.

Benzophenone-containing phosphors with an unprecedented long lifetime of 1.8 s under ambient conditions.

It is well-known that benzophenone has a short phosphorescence lifetime of around 1 ms even at 77 K. Here we report a benzophenone-containing emitter with an unprecedented long phosphorescence lifetime of 1.8 s under ambient conditions, which can be attributed to its T1 state of localized excitation nature as revealed by detailed studies.

Manipulation of Organic Afterglow in Fluoranthene-Containing Dopant-Matrix Systems: From Conventional Room-Temperature Phosphorescence to Efficient Red TADF-Type Organic Afterglow.

It remains challenging to fabricate highly-efficient and long-lived organic afterglow materials, especially in the case of red afterglow systems. Here we develop advanced charge transfer (CT) technology to boost afterglow efficiency and lifetimes in fluoranthene-containing dopant-matrix systems. First, organic CT molecules possess singlet-triplet splitting energy (ΔEST ) of around 0.5 eV, much smaller than localized excitation systems. Second, upon doping into suitable organic matrices, dipole-dipole interactions between 1 CT states and organic matrices reduce 1 CT levels with less effect on 3 CT levels, and thus further narrow ΔEST and enhance intersystem crossing. Third, the rigid planar structure of fluoranthene groups and the rigid microenvironment provided by organic matrices can suppress phosphorescence quenching. Forth, the multiple donor design enables spectral red-shifts to red region and switches on TADF mechanism to improve afterglow efficiency to 13.1 % and maintain afterglow lifetime of 0.1 s. Such high-performance afterglow materials have been rarely explored in reported studies.

Enhancing room-temperature phosphorescence via intermolecular charge transfer in dopant-matrix systems.

Some specific organic dopants have been found to form intermolecular charge transfer complexes with phosphorescence-inactive organic matrices to mediate intersystem crossing of the organic matrices and thus activate room-temperature phosphorescence of the organic matrices. This method of boosting intersystem crossing paves the way for high-performance organic room-temperature phosphorescent materials.

Boosting Organic Afterglow Performance via a Two-Component Design Strategy Extracted from Macromolecular Self-Assembly.

Because intersystem crossing and phosphorescence decay are spin-forbidden in organic systems, it is challenging to obtain high-performance organic afterglow materials. Inspired by two-component design strategy from macromolecular self-assembly, here we report the utilization of synthetic polymers to control the excited state properties of difluoroboron ß-diketonate (BF2bdk) and deuterated BF2bdk compounds for the fabrication of room-temperature organic afterglow materials. The polymer component can interact with BF2bdk excited states by dipole-dipole interactions, lower BF2bdk S1 levels with insignificant effect on T1 levels, reduce ΔEST, and thus enhance intersystem crossing of BF2bdk excited states. The polymer component can also suppress intramolecular motion of BF2bdk triplets and protect BF2bdk triplets from oxygen quenching. The obtained BF2bdk-polymer afterglow materials exhibit emission lifetimes up to 2.2 s and high photoluminescence quantum yields under ambient conditions, display excellent processability and flexibility, and can function as efficient donors for excited state energy transfer to construct red afterglow materials.

Manipulation of Triplet Excited States in Two-Component Systems for High-Performance Organic Afterglow Materials.

The past several years have witnessed the tremendous development of novel chemical structures, new design strategies and intriguing applications in the field of room-temperature phosphorescence (RTP) and organic afterglow materials. This Review article focuses on recent advancements of high-performance organic afterglow materials obtained by two-component design strategies such as a dopant-matrix, donor-acceptor, sensitization, and energy-transfer strategies. Based on some cutting-edge studies, organic afterglow efficiency has been largely improved, exceeding 90 % in several cases. Organic afterglow durations reach tens of seconds in phosphorescence systems and hours in donor-acceptor systems. Organic afterglow brightness outcompetes some inorganic afterglow materials in the first several seconds after ceasing excitation source. Organic afterglow colors cover the whole visible regions and extend to near-infrared regions with respectful afterglow efficiency. On the basis of these achievements, researchers demonstrate promising applications of organic afterglow materials in diverse fields, which has also been reviewed.

Intense Organic Afterglow Enabled by Molecular Engineering in Dopant-Matrix Systems.

We report intense dopant-matrix afterglow systems with an afterglow efficiency (ΦAG) of 47% and an afterglow lifetime (τAG) of 1.3 s. Luminescent difluoroboron ß-diketonate (BF2bdk) dopants and their deuterated counterparts are designed with naphthalene and carboxylic acid groups. After doping into benzoic acid (BA) matrices, room-temperature afterglow brightness and afterglow duration of the BF2bdk-BA materials have unexpectedly been found to reach the levels of those at 77 K, which indicates that hydrogen bonding between BF2bdk and BA, as well as the deuteration technique, can reduce knr + kq of BF2bdk triplets to very small values even at room temperature. Detailed studies reveal that the BF2bdk possesses typical 1ICT characters in the S1 state and distinct 3LE composition in the T1 state, and thus shows a high ΦISC and a small kP to obtain a high ΦAG and a long τAG. Besides, triplet-triplet annihilation has been found in the dopant-matrix system at high doping concentrations to further increase ΦAG.

Manipulation of Organic Afterglow by Thermodynamic and Kinetic Control.

The fabrication of room-temperature organic phosphorescence and afterglow materials, as well as the transformation of their photophysical properties, has emerged as an important topic in the research field of luminescent materials. Here, we report the establishment of energy landscapes in dopant-matrix organic afterglow systems where the aggregation states of luminescent dopants can be controlled by doping concentrations in the matrices and the methods of preparing the materials. Through manipulation by thermodynamic and kinetic control, dopant-matrix afterglow materials with different aggregation states and diverse afterglow properties can be obtained. The conversion from metastable aggregation state to thermodynamic stable aggregation state of the dopant-matrix afterglow materials to leads to the emergence of intriguing afterglow transformation behavior triggered by thermal and solvent annealing. The thermodynamically unfavorable reversible afterglow transformation process can also be achieved by coupling the dopant-matrix afterglow system to mechanical forces.

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) ß-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.

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 (kRISC ) to simultaneously improve afterglow quantum yields and maintain afterglow emission lifetime. Difluoroboron ß-diketonate (BF2 bdk) compounds are designed with multiple electron-donating groups to possess moderate kRISC 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.

Hard yet Flexible Transparent Omniphobic GPOSS Coatings Modified with Perfluorinated Agents.

Transparent materials with glasslike hardness and polymer-like flexibility are highly useful but rare. This paper reports the incorporation of the low-surface-tension pentafluoropropionic acid (FC2-COOH) or tridecafluoroheptanoic acid (FC6-COOH) into a 3-glycidyloxypropyl polyhedral oligomeric silsesquioxane (GPOSS) coating to yield hard/flexible omniphobic coatings. To avoid the macrophase separation of these additives from GPOSS and thus maintain the coating's high transparency, they are first reacted with excess GPOSS via the opening of the glycidyl rings with the carboxy groups to produce mixtures of GPOSS and GPOSS-FC2 or GPOSS-FC6. The fluorinated GPOSS mixtures are then photochemically cured. This study investigates the influence of the type and amount of a fluorinated agent used on the wetting and mechanical properties of the coatings. The wetting properties studied include surface energies, liquid sliding behavior, and repellency against an artificial fingerprint liquid. Meanwhile, the mechanical properties include pencil hardness, Young's modulus, hardness, and resistance to abrasion by steel wool and cheesecloth. Aside from producing coatings that may serve as a viable alternative for the currently used hard/flexible coatings in foldable smartphones, this paper provides guidelines for producing coatings with further improved omniphobicity and wear resistance.

Achieving Purely-Organic Room-Temperature Aqueous Phosphorescence via a Two-Component Macromolecular Self-Assembly Strategy.

Manipulation of supramolecular behaviors and aggregation states represents an important topic in devising intriguing photofunctional systems. Here we report a two-component macromolecular self-assembly strategy for achieving aqueous room-temperature phosphorescence (RTP) in purely organic systems. Amphiphilic triblock copolymers are used to modulate the self-assembly of planar RTP molecules in aqueous solution, leading to the formation of sheet-like RTP objects with well-defined morphology, uniform crystalline nanostructures and excellent aqueous dispersity. In contrast, the addition of the planar RTP molecules into aqueous medium only leads to precipitation and quenching of RTP properties. Powder X-ray diffraction and single-crystal X-ray diffraction studies reveal that the amphiphilic triblock copolymers can assist supramolecular columnar packing of the planar RTP molecules where multiple non-covalent interactions stabilize the triplet excited states. Interestingly, it is found that luminescent signals of the sheet-like RTP objects can be extracted from strong fluorescent environments by phosphorescence mode and emission lifetime measurement.

Heterochiral Self-Discrimination-Driven Supramolecular Self-Assembly of Decanuclear Gold(I)-Sulfido Complexes into 2D Nanostructures with Chiral Anions-Tuned Morphologies.

Chiral self-recognition and self-discrimination are of vital importance to biological processes. In this work, 2D regular rhombic nanocrystals (RS-NC) were fabricated through heterochiral self-discrimination between chiral polynuclear gold(I)-sulfido complex enantiomers, [(R-BINAP)4 Au10 S4 ]Cl2 (R-Au10 ) and [(S-BINAP)4 Au10 S4 ]Cl2 (S-Au10 ), in MeOH without the need for any surfactants or templates. The monitoring of nanocrystals (NCs) formation by TEM and DLS has uncovered the self-assembly process and shape evolution of the NCs and revealed a screw-dislocation dictated spiral growth of the rhombic NCs. Upon addition of chiral anions, the morphology of the gold NCs was found to change from rhombic to strip and quasi-hexagonal nanosheets, arising from reverse and rotational layer-by-layer stacking to give the bilayer NCs. By applying a high temperature, rhombic gold nanoisland films were obtained from the rhombic NCs. The current study has provided a simple strategy towards the construction of regular geometric 2D NCs as well as their chiral anion-tuned and reverse and rotational stacking-determined morphology change by heterochiral self-discrimination.

Platinum(II) Probes for Sensing Polyelectrolyte Lengths and Architectures.

Platinum(II) polypyridine complexes of a square-planar geometry have been used as spectroscopic reporters for quantification of various charged species through non-covalent metal-metal interactions. The characterization of molecular weights and architectures of polyelectrolytes represents a challenging task in polymer science. Here, we report the utilization of platinum(II) complex probes and non-covalent metal-metal interactions for sensing polyelectrolyte lengths and architectures. It is found that the platinum(II) probes can bind to linear polyelectrolytes via electrostatic attractions and give rise to significant spectroscopic changes associated with the formation of metal-metal interactions, and the extent of the spectroscopic changes is found to increase with the lengths of the linear polyelectrolytes. Besides, the platinum(II) probes have been found to co-assemble with the linear polyelectrolytes to form well-defined nanofibers, and the lengths of the linear polyelectrolytes can be directly estimated from the diameter of the nanofibers under transmission electron microscopy observation. Interestingly, upon mixing with the platinum(II) probes, polyelectrolytes with bottlebrush architectures have been found to exhibit larger spectroscopic changes than linear polyelectrolytes with the same chemical composition. Combined with the reported theoretical studies on counterion condensation of polyelectrolytes, the platinum(II) complexes are found to function as spectroscopic probes for sensing the charge densities of the polyelectrolytes with different lengths and diverse architectures. Moreover, platinum(II) probes pre-organized in nanostructured aggregates have been found to intercalate into double-stranded DNA, which are naturally occurring biological polyelectrolytes with helical architectures and intercalation sites, to give significant enhancement of spectroscopic changes when compared to the intercalation of monomeric platinum(II) probes into double-stranded DNA.