An Organophosphorescence Probe with Ultralong Lifetime and Intrinsic Tissue Selectivity for Specific Tumor Imaging and Guided Tumor Surgery.

Organic phosphorescent materials are excellent candidates for use in tumor imaging. However, a systematic comparison of the effects of the intensity, lifetime, and wavelength of phosphorescent emissions on bioimaging performance has not yet been undertaken. In addition, there have been few reports on organic phosphorescent materials that specifically distinguish tumors from normal tissues. This study addresses these gaps and reveals that longer lifetimes effectively increase the signal intensity, whereas longer wavelengths enhance the penetration depth. Conversely, a strong emission intensity with a short lifetime does not necessarily yield robust imaging signals. Building upon these findings, an organo-phosphorescent material with a lifetime of 0.94 s was designed for tumor imaging. Remarkably, the phosphorescent signals of various organic nanoparticles are nearly extinguished in blood-rich organs because of the quenching effect of iron ions. Moreover, for the first time, we demonstrated that iron ions universally quench the phosphorescence of organic room-temperature phosphorescent materials, which is an inherent property of such substances. Leveraging this property, both the normal liver and hepatitis tissues exhibit negligible phosphorescent signals, whereas liver tumors display intense phosphorescence. Therefore, phosphorescent materials, unlike chemiluminescent or fluorescent materials, can exploit this unique inherent property to selectively distinguish liver tumor tissues from normal tissues without additional modifications or treatments.

Recent progress in ion-regulated organic room-temperature phosphorescence.

Organic room-temperature phosphorescence (RTP) materials have attracted considerable attention for their extended afterglow at ambient conditions, eco-friendliness, and wide-ranging applications in bio-imaging, data storage, security inks, and emergency illumination. Significant advancements have been achieved in recent years in developing highly efficient RTP materials by manipulating the intermolecular interactions. In this perspective, we have summarized recent advances in ion-regulated organic RTP materials based on the roles and interactions of ions, including the ion-π interactions, electrostatic interactions, and coordinate interactions. Subsequently, the current challenges and prospects of utilizing ionic interactions for inducing and modulating the phosphorescent properties are presented. It is anticipated that this perspective will provide basic guidelines for fabricating novel ionic RTP materials and further extend their application potential.

Twofold rigidity activates ultralong organic high-temperature phosphorescence.

A strategy is pioneered for achieving high-temperature phosphorescence using planar rigid molecules as guests and rigid polymers as host matrix. The planar rigid configuration can resist the thermal vibration of the guest at high temperatures, and the rigidity of the matrix further enhances the high-temperature resistance of the guest. The doped materials exhibit an afterglow of 40 s at 293 K, 20 s at 373 K, 6 s at 413 K, and a 1 s afterglow at 433 K. The experimental results indicate that as the rotational ability of the groups connected to the guests gradually increases, the high-temperature phosphorescence performance of the doped materials gradually decreases. In addition, utilizing the property of doped materials that can emit phosphorescence at high temperatures and in high smoke, the attempt is made to use organic phosphorescence materials to identify rescue workers and trapped personnel in fires.

π-π Interaction-Induced Organic Long-wavelength Room-Temperature Phosphorescence for In Vivo Atherosclerotic Plaque Imaging.

Room-temperature phosphorescent (RTP) materials have great potential for in vivo imaging because they can circumvent the autofluorescence of biological tissues. In this study, a class of organic-doped long-wavelength (≈600 nm) RTP materials with benzo[c][1,2,5] thiadiazole as a guest was constructed. Both host and guest molecules have simple structures and can be directly purchased commercially at a low cost. Owing to the long phosphorescence wavelength of the doping system, it exhibited good tissue penetration (10 mm). Notably, these RTP nanoparticles were successfully used to image atherosclerotic plaques, with a signal-to-background ratio (SBR) of 44.52. This study provides a new approach for constructing inexpensive red organic phosphorescent materials and a new method for imaging cardiovascular diseases using these materials.

Solid-State Luminescence Stimulus-Responsive Property and Doped RTP Emission of Novel 7a,8,10,11-Tetrahydro-9H- pyrido[2',1':2,3][1,3]oxazino[6,5,4-ij]isoquinoline Derivative.

A novel 7a,8,10,11-tetrahydro-9H-pyrido[2',1':2,3][1,3]-oxazino[6,5,4-ij]isoquinoline derivative (POIQ) is accidentally obtained from an isoquinoline derivative and iodine in dimethyl sulfoxide, which is demonstrated to undergo a mechanism of demethylation and thus intramolecular nucleophilic substitution. POIQ with twisted molecular conformation and loose stacking arrangement shows multifunctional optical properties including dual-state emission, mechanochromic, and solid-state acidochromic activities. Furthermore, an organic room temperature phosphorescence (RTP) doped system with green afterglow of 2 s is constructed using POIQ as the guest and easily available phenyl benzoate as the host, in which the host molecules assist in the transfer of the triplet excitons of the guest molecules. Rewritable optical recording media and information encryption are also realized based on multifunctional optical properties of this compound. This work provides inspiration for the development of N,O-containing fused-ring compounds with fluorescence/RTP properties.

Stimulus-Responsive Organic Phosphorescence Materials Based on Small Molecular Host-Guest Doped Systems.

Small molecular host-guest doped materials exhibit superiority toward high-efficiency room-temperature phosphorescence (RTP) materials due to their structural design diversity and ease of preparation. Dynamic RTP materials display excellent characteristics, such as good reversibility, quick response, and tunable luminescence ability, making them applicable to various cutting-edge technologies. Herein, we summarize the advances in host-guest doped dynamic RTP materials that respond to external and internal stimuli and present some insights into the molecular design strategies and underlying mechanisms. Subsequently, specific viewpoints are described regarding this promising field for the development of dynamic RTP materials. This Perspective is highly beneficial for future intelligent applications of dynamic RTP systems.

Guest-activated quaternary ammonium salt hosts emit room temperature phosphorescence.

A novel doped system based on quaternary ammonium salts as hosts was established. Interestingly, it is the guest-activated hosts that emit room temperature phosphorescence, rather than the host-assisted guests in traditional doped systems.

Unexpected synthesis, delayed emission and solid-state acidochromism of novel 2,7-naphthyridine derivatives obtained from 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile.

Two novel 2,7-naphthyridine derivatives are unexpectedly synthesized by the reaction of 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile and benzylamine, and are achieved through different ring-closing mechanisms. These two derivatives with twisted molecular conformations display phosphorescence, thermally activated delayed fluorescence, and high contrast solid-state acidochromism due to special chemical structures.

Metal Ions as the Third Component Coordinate with the Guest to Stereoscopically Enhance the Phosphorescence Properties of Doped Materials.

The construction of multicomponent doped systems is an important direction for the development of phosphorescence materials. Herein, benzophenone is selected as the host, phenylquinoline isomers are designed as guests, and seven metal ions are selected as the third component (Al3+, Cu+/2+, Zn2+, Ga3+, Ag+, Cd2+, and In3+) to construct the three-component doped system. Ag+ and Cd2+ can considerably increase the emission intensity up to 38 times, and the highest phosphorescence quantum efficiency reaches 70%. Al3+, Ga3+, and In3+ can prolong the emission wavelength, and the phosphorescence wavelength can be red-shifted up to 60 nm. Cu2+, Ga3+, and In3+ can extend the phosphorescence lifetime by a maximum of 3.6 times. A series of experiments demonstrated that the coordination of metals and guests is the key to improve the phosphorescence properties. This work presents a simple and effective strategy to enhance the phosphorescence properties of doped materials.

Boosted Productivity in Single-Tile-Based DNA Polyhedra Assembly by Simple Cation Replacement.

Cations such as divalent magnesium ion (Mg2+ ) play an essential role in DNA self-assembly. However, the strong electrostatic shielding effect of Mg2+ would be disadvantageous in some situations that require relatively weak interactions to allow a highly reversible error-correcting mechanism in the process of assembly. Herein, by substituting the conventional divalent Mg2+ with monovalent sodium ion (Na+ ), we have achieved one-pot high-yield assembly of tile-based DNA polyhedra at micromolar concentration of tiles, at least 10 times higher than the DNA concentrations reported previously. This strategy takes advantage of coexisting counterions and is expected to surmount the major obstacle to potential applications of such DNA nanostructures: large-scale production.

Halogen Bonding: A New Platform for Achieving Multi-Stimuli-Responsive Persistent Phosphorescence.

Monotonous luminescence has always been a major factor limiting the application of organic room-temperature phosphorescence (RTP) materials. Enhancing and regulating the intermolecular interactions between the host and guest is an effective strategy to achieve excellent phosphorescence performance. In this study, intermolecular halogen bonding (CN⋅⋅⋅Br) was introduced into the host-guest RTP system. The interaction promoted intersystem crossing and stabilized the triplet excitons, thus helping to achieve strong phosphorescence emission. In addition, the weak intermolecular interaction of halogen bonding is sensitive to external stimuli such as heat, mechanical force, and X-rays. Therefore, the triplet excitons were easily quenched and colorimetric multi-stimuli responsive behaviors were realized, which greatly enriched the luminescence functionality of the RTP materials. This method provides a new platform for the future design of responsive RTP materials based on weak intermolecular interactions between the host and guest molecules.

Construction of Mechanofluorochromic and Aggregation-Induced Emission Materials Based on 4-Substituted Isoquinoline Derivatives.

Although many organic mechanofluorochromic (MFC) materials have been reported, the design strategy and formation mechanism are still unclear, and thus some of their discoveries are based on chance or a result of blind screening of some compounds. Herein, we show a strategy for constructing MFC materials from a multisubstituted isoquinoline compound with excellent crystallinity. The introduction of bromine atom at 4-position realizes the morphological change from crystalline state to amorphous state under the stimulation of external pressure, but it is not enough to generate MFC phenomenon. Similarly, although naphthalene, benzofuran, and benzothiophene endow the resultant isoquinolines with twisted molecular conformations and aggregation-induced emission (AIE) activities, no obvious solid-state emission color changes are observed. However, the introduction of 2-benzylidenemalononitrile and (E)-2-cyano-3-phenylacrylate leads not only to the AIE activities of IQ-M and IQ-A, but also to their outstanding and reversible MFC properties. The MFC activities of these two derivatives are demonstrated to come from more twisted molecular conformations, larger deformation spaces, and stronger intramolecular charge transfer compared with the other isoquinolines. This work offers important reference value for the construction of MFC and AIE materials from traditional fluorophores.

Guest-host doped strategy for constructing ultralong-lifetime near-infrared organic phosphorescence materials for bioimaging.

Organic near-infrared room temperature phosphorescence materials have unparalleled advantages in bioimaging due to their excellent penetrability. However, limited by the energy gap law, the near-infrared phosphorescence materials (>650 nm) are very rare, moreover, the phosphorescence lifetimes of these materials are very short. In this work, we have obtained organic room temperature phosphorescence materials with long wavelengths (600/657-681/732 nm) and long lifetimes (102-324 ms) for the first time through the guest-host doped strategy. The guest molecule has sufficient conjugation to reduce the lowest triplet energy level and the host assists the guest in exciton transfer and inhibits the non-radiative transition of guest excitons. These materials exhibit good tissue penetration in bioimaging. Thanks to the characteristic of long lifetime and long wavelength emissive phosphorescence materials, the tumor imaging in living mice with a signal to background ratio value as high as 43 is successfully realized. This work provides a practical solution for the construction of organic phosphorescence materials with both long wavelengths and long lifetimes.

Selenium atoms induce organic doped systems to produce pure phosphorescence emission.

A host-guest system is constructed using a guest containing two selenium atoms. The selenium atoms can increase the spin-orbit coupling constant and the conjugation degree, thereby increasing the emission wavelength, and making the materials show only phosphorescence emission.

Influence of Guest/Host Morphology on Room Temperature Phosphorescence Properties of Pure Organic Doped Systems.

Guest/host phosphorescence materials have attracted much attention; traditionally, researchers have focused on the influence of the electronic properties and energy levels of the molecules on the phosphorescence activities. However, the effects of the morphology on the phosphorescence properties are ignored. Herein, three isoquinoline guests with different aliphatic rings and three hosts are selected to construct guest/host materials. Experimental results confirm that the guests are dispersed in the host in the form of clusters. More importantly, the morphologies of the guest/host directly affect the phosphorescence properties. In these systems, the guests have strong intermolecular interactions, which are beneficial to stabilize the triplet excitons; meanwhile, the hosts should have weak intermolecular interactions with easily changed morphology to accept the guest clusters, which synergistically ensure that the doped materials have excellent RTP properties. This is the first work focusing on the effect of molecular morphology on the phosphorescence characteristics of guest/host systems.

Efficient and organic host-guest room-temperature phosphorescence: tunable triplet-singlet crossing and theoretical calculations for molecular packing.

Organic host-guest doped materials exhibiting the room temperature phosphorescence (RTP) phenomenon have attracted considerable attention. However, it is still challenging to investigate their corresponding luminescence mechanism, because for host-guest systems, it is very difficult to obtain single crystals compared to single-component or co-crystal component materials. Herein, we developed a series of organic doped materials with triphenylamine (TPA) as the host and TPA derivatives with different electron-donating groups as guests. The doped materials showed strong fluorescence, thermally activated delayed fluorescence (τ: 39-47 ms), and efficient room temperature phosphorescence (Φ phos: 7.3-9.1%; τ: 170-262 ms). The intensity ratio between the delayed fluorescence and phosphorescence was tuned by the guest species and concentration. Molecular dynamics simulations were used to simulate the molecular conformation of guest molecules in the host matrix and the interaction between the host and guest molecules. Therefore, the photophysical properties were calculated using the QM/MM model. This work provides a new concept for the study of molecular packing of guest molecules in the host matrix.

Excitation-Dependent Triplet-Singlet Intensity from Organic Host-Guest Materials: Tunable Color, White-Light Emission, and Room-Temperature Phosphorescence.

A series of organic host-guest materials with multifunctional luminescence were constructed. Four isoquinoline derivatives were used as the guests, and benzophenone was used as the host. The doped system exhibited excellent dual emission with cyan fluorescence and orange-yellow room-temperature phosphorescence, and the dual emission could be combined into almost pure white-light emission. Importantly, the relative intensity of the fluorescence-phosphorescence could be adjusted by changing the excitation wavelength, with the phosphorescence intensity being significantly higher than the fluorescence intensity under shorter excitation wavelengths and vice versa under longer excitation wavelengths. Therefore, three-color emission switching among cyan, white, and orange could be achieved by simply adjusting the excitation wavelength. The results of experimental and theoretical calculations indicated that the excitation-dependent emission colors were caused by different transfer paths for excitons under different excitation wavelengths. These materials with multifunctional luminescence could be used as writable inks for advanced anticounterfeiting.

Multifunctional properties of a star-shaped triphenylamine-benzene-1,3,5-tricarbohydrazide fluorescent molecule containing multiple flexible chains.

A star-shaped triphenylamine-benzene-1,3,5-tricarbohydrazide molecule with a twisted molecular conformation was found to display amazing multifunctional optical properties. The design of peripheral triphenylamine units and a central benzene connected with hydrazide groups leads to the formation of rare polymorphic properties in the presence of multiple flexible chains. Two polymorphs with different fluorescence colors exhibited bathochromic mechanofluorochromic activities with high contrast due to a crystalline-to-amorphous transition.

Tunable Phosphorescence/Fluorescence Dual Emissions of Organic Isoquinoline-Benzophenone Doped Systems by Alkoxy Engineering.

Dual/multi-component organic doped systems with room-temperature phosphorescence (RTP) properties have been developed. However, the unknown luminescence mechanism still greatly limits the development of the doped materials. Herein, a new doped system exhibiting phosphorescence/fluorescence dual emission (Φphos =4-24 % and τphos =101-343 ms) is successfully constructed through prediction and design. A series of isoquinoline derivatives with different alkoxy chains were selected as the guests. Benzophenone was chosen as the host owing to the characteristics of low melting point and good crystallinity. The alkoxy chain lengths of the guests are first reported to be used to control the fluorescence and phosphorescence intensities of the doped materials, which results in different prompt emission colors. Additionally, the doped ratio of the guest and host can also control the luminous intensities of the materials. In particular, the doped materials still exhibit phosphorescent properties even if the ratio of the guest/host is as low as 1:100 000.

An Unexpected 4,5-Diphenyl-2,7-naphthyridine Derivative with Aggregation-Induced Emission and Mechanofluorochromic Properties Obtained from a 3,5-Diphenyl-4H-pyran Derivative.

For a specific fluorescent molecule, the increase of molecular conformation distortion is beneficial to endow it with aggregation-induced emission (AIE) and mechanofluorochromic (MFC) properties. Herein, 3,5-diphenyl-4H-pyran derivative 5 and 4,5-diphenyl-2,7-naphthidine derivative 7 with highly twisted conformations were synthesized. For compound 5, although the introduction of phenyl rings with large steric hindrance at 3 and 5 positions of the 4H-pyran skeleton realized the transformation from aggregation-induced quenching (ACQ)-active molecule to AIE-active molecule, it only showed a low-contrast MFC activity. Compound 7 was accidentally obtained from compound 5 and n-butylamine via a ring-opening and subsequent intramolecular ring-closing mechanism. Compound 7 was confirmed to have a highly twisted molecular conformation by the crystal structural analysis and exhibited AIE activity originated from the restriction of intramolecular rotation. Furthermore, compound 7 exhibited reversible high-contrast MFC activity. Upon grinding, the change of solid-state fluorescence color from orange to yellow was confirmed to be due to the partial destruction of crystal structure. This work provides new ideas for the design and synthesis of novel AIE-active and MFC-active fluorescent molecules based on ACQ-active parent molecules.