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.     

Manipulating the Ultralong Organic Phosphorescence of Small Molecular Crystals

Ultralong organic phosphorescence (UOP) of metal-free organic materials has received considerable attention recently owing to their long-lived emission lifetimes, and the fact that they present an attractive alternative to persistent luminescence in inorganic phosphors. Enormous research effort has been devoted on improving UOP performance in metal-free organic phosphors by promoting the intersystem crossing (ISC) process and suppressing the non-radiative decay of triplet state excitons. This minireview summarizes the recent advances in the rational approaches for manipulating the UOP properties of small molecular crystals, such as phosphorescence lifetime, efficiency, and emission colors. Finally, the present challenges and future development of this field are proposed. This review will provide a guideline to rationally design more advanced metal-free organic phosphorescence materials for potential applications.     

Dynamic Ultralong Organic Phosphorescence by Photoactivation

Smart materials with ultralong phosphorescence are rarely investigated and reported. Herein we report on a series of molecules with unique dynamic ultralong organic phosphorescence (UOP) features, enabled by manipulating intermolecular interactions through UV light irradiation. Our experimental data reveal that prolonged irradiation of single‐component organic phosphors of PCzT, BCzT, and FCzT under ambient conditions can activate UOP with emission lifetimes spanning from 1.8 to 1330 ms. These phosphors can also be deactivated back to their original states with short‐lived phosphorescence by UV irradiation for 3 h at room temperature or through thermal treatment. Additionally, the dynamic UOP was applied successfully for a visual anti‐counterfeiting application. These findings may provide unique insight into dynamic molecular motion for optical processing and expand the scope of smart‐response materials for broader applications.     

Manipulating the Stacking of Triplet Chromophores in the Crystal Form for Ultralong Organic Phosphorescence

Provided here is evidence showing that the stacking between triplet chromophores plays a critical role in ultralong organic phosphorescence (UOP) generation within a crystal. By varying the structure of a functional unit, and different on‐off UOP behavior was observed for each structure. Remarkably, 24CPhCz, having the strongest intermolecular interaction between carbazole units exhibited the most impressive UOP with a long lifetime of 1.06 s and a phosphorescence quantum yield of 2.5 %. 34CPhCz showed dual‐emission UOP and thermally activated delayed fluorescence (TADF) with a moderately decreased phosphorescence lifetime of 770 ms, while 35CPhCz only displayed TADF owing to the absence of strong electronic coupling between triplet chromophores. This study provides an explanation for UOP generation in crystal and new guidelines for obtaining UOP materials.     

Subtle structure tailoring of metal-free triazine luminogens for highly efficient ultralong organic phosphorescence

Ultralong organic phosphorescent materials have invoked considerable attention for their great potential in sensing, data encryption, information anti-counterfeiting and so forth. However, effective ways to achieve highly efficient ultralong organic phosphorescence (UOP) in metal-free organic materials remain a great challenge. Herein, we designed three isomers based on asymmetric triazines with various bromine substituted positions. Impressively, phosphorescence efficiency of p-BrAT in solid state can reach up to 9.7% with a long lifetime of 386 ms, which was one of the highest efficient UOP materials reported so far. Theoretical calculations further demonstrated that para-substitution exhibited the most effective radiative transition for triplet excitons. These results will provide an effective approach to achieving highly efficient UOP materials.     

Subtle structure tailoring of metal-free triazine luminogens for highly efficient ultralong organic phosphorescence

Highly efficient ultralong organic phosphorescence (UOP) based on a series of metal-free triazine luminogens was achieved via subtly structural tailoring of bromine substituted positions.Impressively,p-BrAT in solid state displayed high phosphorescence efficiency up to 9.7% with a long lifetime of 386 ms,which was one of the highest efficient UOP materials reported so far in metal-free compounds.     

Ultralong Phosphorescence from Organic Ionic Crystals under Ambient Conditions

A new type of materials, organic salts in the crystal state, have ultralong organic phosphorescence (UOP) under ambient conditions. The change of cations (NH₄⁺, Na⁺, or K⁺) in these phosphors gives access to tunable UOP colors ranging from sky blue to yellow green, along with ultralong emission lifetimes of over 504 ms. Single‐crystal analysis reveals that unique ionic bonding can promote an ordered arrangement of organic salts in crystal state, which then can facilitate molecular aggregation for UOP generation. Additionally, reversible ultralong phosphorescence can be realized through the alternative employment of fuming gases (ammonia and hydrogen chloride), demonstrating its potential as a candidate for visual ammonic or hydrogen chloride gas sensing. The results provide an environmental responsible and practicable synthetic approach to expanding the scope of ultralong organic phosphorescent materials as well as their applications.     

Regioisomerism effect (RIE) on optimizing ultralong organic phosphorescence lifetimes

Regioisomerism effect was disclosed on optimizing ultralongorganic phosphorescence life times of three crystalline dicarbazol-9-yl pyrazine-based regioisomers (p-DCzP,m-DCzP,and o-DCzP) with para-,meta-, and ortho-convergent substitutions.It is revealed that regioisomerism effect could be an effective strategy for the deep understanding of UOP materials.     

Boosting the Quantum Efficiency of Ultralong Organic Phosphorescence up to 52 % via Intramolecular Halogen Bonding

Ultralong organic phosphorescence (UOP) has attracted increasing attention due to its potential applications in optoelectronics, bioelectronics, and security protection. However, achieving UOP with high quantum efficiency (QE) over 20 % is still full of challenges due to intersystem crossing (ISC) and fast non-radiative transitions in organic molecules. Here, we present a novel strategy to enhance the QE of UOP materials by modulating intramolecular halogen bonding via structural isomerism. The QE of CzS2Br reaches up to 52.10 %, which is the highest afterglow efficiency reported so far. The crucial reason for the extraordinary QE is intramolecular halogen bonding, which can not only effectively enhance ISC by promoting spin–orbit coupling, but also greatly confine motions of excited molecules to restrict non-radiative pathways. This work provides a reasonable strategy to develop highly efficient UOP materials for practical applications.     

Boosting the Quantum Efficiency of Ultralong Organic Phosphorescence up to 52 % via Intramolecular Halogen Bonding

Ultralong organic phosphorescence (UOP) has attracted increasing attention due to its potential applications in optoelectronics, bioelectronics, and security protection. However, achieving UOP with high quantum efficiency (QE) over 20 % is still full of challenges due to intersystem crossing (ISC) and fast non‐radiative transitions in organic molecules. Here, we present a novel strategy to enhance the QE of UOP materials by modulating intramolecular halogen bonding via structural isomerism. The QE of CzS2Br reaches up to 52.10 %, which is the highest afterglow efficiency reported so far. The crucial reason for the extraordinary QE is intramolecular halogen bonding, which can not only effectively enhance ISC by promoting spin–orbit coupling, but also greatly confine motions of excited molecules to restrict non‐radiative pathways. This work provides a reasonable strategy to develop highly efficient UOP materials for practical applications.     

Hydrogen‐Bonded Organic Aromatic Frameworks for Ultralong Phosphorescence by Intralayer π–π Interactions

Ultralong organic phosphorescence (UOP) based on metal‐free porous materials is rarely reported owing to rapid nonradiative transition under ambient conditions. In this study, hydrogen‐bonded organic aromatic frameworks (HOAFs) with different pore sizes were constructed through strong intralayer π–π interactions to enable ultralong phosphorescence in metal‐free porous materials under ambient conditions for the first time. Impressively, yellow UOP with a lifetime of 79.8 ms observed for PhTCz‐1 lasted for several seconds upon ceasing the excitation. For PhTCz‐2 and PhTCz‐3, on account of oxygen‐dependent phosphorescence quenching, UOP could only be visualized in N₂, thus demonstrating the potential of phosphorescent porous materials for oxygen sensing. This result not only outlines a principle for the design of new HOFs with high thermal stability, but also expands the scope of metal‐free luminescent materials with the property of UOP.     

Regioisomerism effect (RIE) on optimizing ultralong organic phosphorescence lifetimes

Organic phosphorescence materials demonstrate potential optoelectronic applications due to their remarkably ultralong organic phosphorescence (UOP) lifetime and abundant optical characteristics prior to the fluorescence materials. For a better insight into the intrinsic relationship among regioisomeric molecules, crystalline interactions, and phosphorescence properties, three crystalline dicarbazol-9-yl pyrazine-based regioisomers with para-, meta-, and ortho-convergent substitutions (p-DCzP, m-DCzP, and o-DCzP) were designed and presented gradually increased UOP lifetimes prolonging from 63.14, 127.93 to 350.46 ms, respectively, due to the regioisomerism effect (RIE) which would be an effective strategy for better understanding of structure-property of UOP materials.     

Crosslink-enhanced strategy to achieve multicolor long-lived room temperature phosphorescent films with excellent photostability

Room temperature phosphorescence (RTP) films have recently attracted increasing attention due to their excellent luminescent properties for information encryption, optoelectronic devices, and sensors. However, polyvinyl alcohol (PVA) films with abundant hydrogen bonds to suppress triplet energy dissipation suffered from the humidity induced phosphorescence quenching under storage in the air for a long time. In this work, poly(acrylic acid) (PAA) was selected to crosslink PVA matrix through esterification reactions for preparing water resistant RTP films. The blue, cyan, and orange emissive RTP films were successfully obtained by incorporating three different organic compounds into PVA-PAA crosslinking films. Crosslinking strategy significantly improved the phosphorescence emissions of the doped films, and effectively blocked the absorption of water molecular, leading to the excellent photostability of the developed films. As a proof of concept, the white light phosphorescence film and anti-counterfeiting applications were successfully demonstrated.     

Light‐Controlled Formation of Vesicles and Supramolecular Organogels by a Cholesterol‐Bearing Amphiphilic Molecular Switch

A new responsive material composed of an amphiphilic light‐switchable dithienylethene unit functionalized with a hydrophobic cholesterol unit and a hydrophilic poly(ethylene glycol)‐modified pyridinium group has been designed. This unique single‐molecule system shows responsive light‐switchable self‐assembly in both water and organic solvents. Light‐triggered reversible vesicle formation in aqueous solutions is reported. The molecule shows a different behavior in apolar aromatic solvents, in which light‐controlled formation of organogel fibers is observed. The light‐triggered aggregation behavior of this molecule demonstrates that control of a supramolecular structure with light can be achieved in both aqueous and organic media and that this ability can be present in a single molecule. This opens the way toward the effective development of new strategies in soft nanotechnology for applications in controlled chemical release systems.     

Color-tunable ultralong organic phosphorescence materials for visual UV-light detection

Ultralong organic phosphorescence(UOP) materials have roused considerable attention in the field of photonics and optoelectronics owing to the feature of long-lived emission lifetimes. However, to develop UOP materials with color-tunability is still a formidable challenge. Here, we report a class of UOP materials containing carbonyl, amino or amide groups, exhibiting colortunable persistent luminescence ranging from blue(458 nm) to yellow-green(508 nm) under different UV wavelength excitation. Taken theoretical and experimental results together, we conclude that the excitation dependent color-tunable UOP emission is ascribed to multiple emission centers from single molecular and aggregated states in crystal. Given color-tunable UOP feature, these materials are used to successfully realize visual UV-light detection. This finding not only provides a strategy to design new organic phosphorescent molecules with colorful emission, but also extends the scope of the applications of purely organic phosphorescent materials.     

Visible-light-excited long-lived organic room-temperature phosphorescence of phenanthroline derivatives in PVA matrix by H-bonding interaction for security applications

Organic room-temperature phosphorescence (RTP) materials are very attractive, but there is still a challenge to achieve RTP for their practical applications under visible light excitation (λ > 400 nm) because of the implement for the most organic RTP is under ultraviolet light. Herein, a simple tactics for inhibiting the vibrational dissipation of three amorphous phenanthroline derivatives by doping them into polyvinyl alcohol (PVA) matrix was utilized to afford visible-light excitation RTP. By using this method, on account of the mutual H-bonding and confinement effect with PVA matrix, a series of organic RTP materials with blue-green phosphorescence emission were obtained under visible-light excitation. The afterglow colors of RTP materials can be adjusted by co-doping the available fluorescence dyes (RhB or Rh6G) into the PVA films through a triplet-to-singlet Förster resonance energy transfer. However, the H-bonding is easily broken by water molecules resulting in the RTP phenomenon disappears. Hence, Aphen-epoxy resin composite system was constructed to overcome this drawback. It is shown that the composite still has good phosphorescence properties after soaking in water for 7 days. The superior RTP of the amorphous phenanthroline derivatives in processable polymer matrices endows these materials with a highly potential for the night warning clothing coating and information encryption.     

A Conventional Surfactant Becomes CO2‐Responsive in the Presence of Switchable Water Additives

We have developed a new benign means of reversibly breaking emulsions and latexes by using “switchable water”, an aqueous solution of switchable ionic strength. The conventional surfactant sodium dodecyl sulfate (SDS) is not normally stimuli‐responsive when CO₂ is used as the stimulus but becomes CO₂‐responsive or “switchable” in the presence of a switchable water additive. In particular, changes in the air/water surface tension and oil/water interfacial tension can be triggered by addition and removal of CO₂. A switchable water additive, N,N‐dimethylethanolamine (DMEA), was found to be an effective and efficient additive for the reversible reduction of interfacial tension and can lower the tension of the dodecane/water interface in the presence of SDS surfactant to ultra‐low values at very low additive concentrations. Switchable water was successfully used to reversibly break an emulsion containing SDS as surfactant, and dodecane as organic liquid. Also, the addition of CO₂ and switchable water can result in aggregation of polystyrene (PS) latexes; the later removal of CO₂ neutralizes the DMEA and decreases the ionic strength allowing for the aggregated PS latex to be redispersed and recovered in its original state.     

Visible Light‐Triggered Photoswitchable Diarylethene‐Based Iridium(III) Complexes for Imaging Living Cells

A novel diarylethene‐based iridium(III) complex was synthesized as a phosphorescence probe for monitoring living cells. The switchable phosphorescence complex in solution and within living cells was controlled by two distinguishable visible‐light irradiations, which suggests that this complex can be developed as a promising probe with weak photodamage for biological samples.     

Modified Electrodes and Electrochemical Systems Switchable by Temperature Changes

This article is an overview of extensive research efforts in the area of temperature‐controlled electrochemical systems. Electrochemical reactions, including electrocatalytic and bioelectrocatalytic processes, have been reversibly activated and inhibited by temperature changes. This was achieved by modification of electrode surfaces with thermo‐sensitive polymers (e.g., poly(N‐isopropylacrylamide), PNIPAM) which are reversibly switched by temperature changes between two different structures: swollen expanded coil conformation and shrunken collapsed globule state. While the swollen hydrophilic state allows penetration of redox species to the electrode conducting support and activates electrochemical reactions, the collapsed hydrophobic state isolates the electrode surface and inhibits electrochemical processes. Electrodes modified with the thermo‐switchable polymers have been additionally functionalized with photo‐switchable molecules (e.g., spiropyran derivatives) to achieve double‐controlled electrochemical reactions switchable by temperature changes and light signals. Incorporation of metallic nanoparticles or graphene species in the temperature‐sensitive polymer films resulted in sophisticated features and multi‐signal controlled behavior of the nano‐composite systems.     

Growth of porous anodic alumina films in hot phosphate–glycerol electrolyte

Growth of porous anodic alumina films has been examined at 10 V in hot phosphate-containing glycerol electrolyte containing 0.1 to 0.57 mass% water. The growth rate of the films is highly dependent upon the water content of the electrolyte, reducing markedly at a water content of 0.1 mass%, an opposite trend to that found previously for the formation of porous films on titanium and niobium. Chemical dissolution of the anodic alumina is also suppressed in electrolyte of low water content. GDOES depth profiles revealed that an increased water content of the electrolyte promoted the incorporation of phosphorus species into the films, although chemical dissolution reduced the amounts of phosphorus in the outer regions. Carbon species also appeared to be present in films, particularly at lower water content. Using a niobium oxide outer layer to suppress chemical dissolution resulted in films that were about 1.2 times the thickness of the consumed aluminium for an electrolyte containing 0.25 mass% water. The expansion suggests a possible contribution of field-assisted flow of film material in the growth of the porous anodic film.