σ-Conjugation and H-Bond-Directed Supramolecular Self-Assembly: Key Features for Efficient Long-Lived Room Temperature Phosphorescent Organic Molecular Crystals

MolPackL: Quantification and Interpretation of Intermolecular Interactions Driven by Molecular Packing

In organic optoelectronic devices, the properties of the aggregated organic materials depend not only on individual molecules or monomers but also significantly on their packing modes. Different from their inorganic counterparts linked by explicit covalent bonds, organic solids exhibit intricate and numerous intermolecular interactions (IMIs). Due to the intrinsic complexity and disorder of IMIs, identifying and understanding them is a formidable challenge in experimental, theoretical, and data-driven approaches. In this work, we constructed an innovative algorithm framework, Molecular Packing Learning (MolPackL), which can accurately quantify elusive IMIs using contact density histograms (CDHs) and efficiently extract intermolecular features for further property prediction of organic solids. It performs satisfactorily in training predictive models of IMI-related properties in molecular crystals. Particularly, the band gap predictive model based on MolPackL achieved the best-reported performance, with an MAE of 0.20 eV and an impressive R2 of 0.92. Class activation mapping (CAM) visually demonstrates MolPackL's accurate identification of effective interaction sites as the molecular packing changes. What is more, the elemental importance analysis verified that the superior score benefits from MolPackL's ability to comprehensively consider multiple influencing factors of IMIs. In summary, MolPackL provides a new framework for quantitative assessment and understanding of the effect of IMIs. The development of MolPackL marks a significant advancement in establishing predictive models of molecular aggregates, deepening the comprehension of IMIs on the material properties. Given the superior performance, we believe that MolPackL will also become a powerful tool in the design of high-performance organic optoelectronic materials.

Enhancing Purely Organic Room Temperature Phosphorescence via Supramolecular Self-Assembly

Long-lived and highly efficient room temperature phosphorescence (RTP) materials are in high demand for practical applications in lighting and display, security signboards, and anti-counterfeiting. Achieving RTP in aqueous solutions, near-infrared (NIR) phosphorescence emission, and NIR-excited RTP are crucial for applications in bio-imaging, but these goals pose significant challenges. Supramolecular self-assembly provides an effective strategy to address the above problems. This review focuses on the recent advances in the enhancement of RTP via supramolecular self-assembly, covering four key aspects: small molecular self-assembly, cocrystals, the self-assembly of macrocyclic hosts and guests, and multi-stage supramolecular self-assembly. This review not only highlights progress in these areas but also underscores the prominent challenges associated with developing supramolecular RTP materials. The resulting strategies for the development of high-performance supramolecular RTP materials are discussed, aiming to satisfy the practical applications of RTP materials in biomedical science.

Large-Scale Preparation for Multicolor Stimulus-Responsive Room-Temperature Phosphorescence Paper via Cellulose Heterogeneous Reaction

The large-scale preparation of sustainable room-temperature phosphorescence (RTP) materials, particularly those with stimulus-response properties, is attractive but remains challenging. This study develops a facile heterogeneous B─O covalent bonding strategy to anchor arylboronic acid chromophores to cellulose chains using pure water as a solvent, resulting in multicolor RTP cellulose. The rigid environment provided by the B─O covalent bonds and hydrogen bonds promotes the triplet population and suppresses quenching, leading to an excellent lifetime of 1.42 s for the target RTP cellulose. By increasing the degree of chromophore conjugation, the afterglow colors can be tuned from blue to green and then to red. Motivated by this finding, a papermaking production line is built to convert paper pulp reacted with an arylboronic acid additive into multicolor RTP paper on a large scale. Furthermore, the RTP paper is sensitive to water because of the destruction of hydrogen bonds, and the stimuli-response can be repeated in response to water/heat stimuli. The RTP paper can be folded into 3D afterglow origami handicrafts and anti-counterfeiting packing boxes or used for stimulus-responsive information encryption. This success paves the way for the development of large-scale, eco-friendly, and practical stimuli-responsive RTP materials.

Redox-Responsive Lipidic Prodrug Nano-Delivery System Improves Antitumor Effect of Curcumin Derivative C210

The poor bioavailability of curcumin and its derivatives limits their antitumor efficacy and clinical translation. Although curcumin derivative C210 has more potent antitumor activity than curcumin, it has a similar deficiency to curcumin. In order to improve its bioavailability and accordingly enhance its antitumor activity in vivo, we developed a redox-responsive lipidic prodrug nano-delivery system of C210. Briefly, we synthesized three conjugates of C210 and oleyl alcohol (OA) via different linkages containing single sulfur/disulfide/carbon bonds and prepared their nanoparticles using a nanoprecipitation method. The prodrugs required only a very small amount of DSPE-PEG2000 as a stabilizer to self-assemble in aqueous solution to form nanoparticles (NPs) with a high drug loading capacity (~50%). Among them, the prodrug (single sulfur bond) nanoparticles (C210-S-OA NPs) were the most sensitive to the intracellular redox level of cancer cells; therefore, they could rapidly release C210 in cancer cells and thus had the strongest cytotoxicity to cancer cells. Furthermore, C210-S-OA NPs exerted a dramatic improvement in its pharmacokinetic behavior; that is, the area under the curve (AUC), mean retention time and accumulation in tumor tissue were 10, 7 and 3 folds that of free C210, respectively. Thus, C210-S-OA NPs exhibited the strongest antitumor activity in vivo than C210 or other prodrug NPs in mouse models of breast cancer and liver cancer. The results demonstrated that the novel prodrug self-assembled redox-responsive nano-delivery platform was able to improve the bioavailability and antitumor activity of curcumin derivative C210, which provides a basis for further clinical applications of curcumin and its derivatives.

D-O-A based organic phosphors for both aggregation-induced electrophosphorescence and host-free sensitization

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes.

Critical roles of linker length in determining the chemical and self-assembly stability of SN38 homodimeric nanoprodrugs

Homodimeric prodrug nanoassemblies (HDPNs) have been widely studied for efficient cancer therapy by virtue of their ultra-high drug loading and distinct nanostructure. However, the development of SN38 HDPNs is still a great challenge due to the rigid planar aromatic ring structure. Improving the structural flexibility of homodimeric prodrugs by increasing the linker length may be a potential strategy for constructing SN38 HDPNs. Herein, three SN38 homodimeric prodrugs with different linker lengths were synthesized. The number of carbon atoms from the disulfide bond to the adjacent ester bond is 1 (denoted as α-SN38-SS-SN38), 2 (β-SN38-SS-SN38), and 3 (γ-SN38-SS-SN38), respectively. Interestingly, we found that α-SN38-SS-SN38 exhibited extremely low yield and poor chemical stability. Additionally, β-SN38-SS-SN38 demonstrated suitable chemical stability but poor self-assembly stability. In comparison, γ-SN38-SS-SN38 possessed good chemical and self-assembly stability, thereby improving the tumor accumulation and antitumor efficacy of SN38. We developed the SN38 HDPNs for the first time and illustrated the underlying molecular mechanism of increasing the linker length to enhance the chemical and self-assembly stability of homodimeric prodrugs. These findings would provide new insights for the rational design of HDPNs with superior performance.

Controlled Growth and Self-Assembly of Multiscale Organic Semiconductor

Currently, organic semiconductors (OSs) are widely used as active components in practical devices related to energy storage and conversion, optoelectronics, catalysis, and biological sensors, etc. To satisfy the actual requirements of different types of devices, chemical structure design and self-assembly process control have been synergistically performed. The morphology and other basic properties of multiscale OS components are governed on a broad scale from nanometers to macroscopic micrometers. Herein, the up-to-date design strategies for fabricating multiscale OSs are comprehensively reviewed. Related representative works are introduced, applications in practical devices are discussed, and future research directions are presented. Design strategies combining the advances in organic synthetic chemistry and supramolecular assembly technology perform an integral role in the development of a new generation of multiscale OSs.

Halogen-doped phosphorescent carbon dots for grayscale patterning

Flexible organic materials that exhibit dynamic ultralong room temperature phosphorescence (DURTP) via photoactivation have attracted increasing research interest for their fascinating functions of reversibly writing-reading-erasing graphic information in the form of a long afterglow. However, due to the existence of a nonnegligible activation threshold for the initial exposure dose, the display mode of these materials has thus far been limited to binary patterns. By resorting to halogen element doping of carbon dots (CDs) to enhance intersystem crossing and reduce the activation threshold, we were able to produce, for the first time, a transparent, flexible, and fully programmable DURTP composite film with a reliable grayscale display capacity. Examples of promising applications in UV photography and highly confidential steganography were constructed, partially demonstrating the broad future applications of this material as a programmable platform with a high optical information density.

Design of Stimuli-Responsive Phenothiazine Derivatives with Triplet-Related Dual Emission and High-Contrast Mechanochromism Guided by Polymorph Prediction

The development of high-contrast stimulus-responsive materials with excited triplet emission is of great significance for anti-counterfeiting, sensor and memory applications, but remains a challenge. Here, we report a strategy for the rational design of stimulus-responsive phenothiazine derivatives with triplet-related dual emissions and high-contrast mechanochromism guided by Polymorph Prediction. The designed phenothiazine derivatives have the characters of simple structures, a facile synthetic procedure, and a good crystalline nature. We found that the crystals of those derivatives with the potential to form both quasi-axial (ax) and quasi-equatorial (eq) conformations could undergo conformation transition and show significant emission difference (Δλ_em >100 nm) under mechanical force. Meanwhile, all these phenothiazine derivatives exhibit aggregation-induced emission and emit room-temperature phosphorescence or thermally activated delayed fluorescence. The significant luminescent change of these materials under different stimuli gives them promise for applications in encryption and anti-counterfeiting.

Irreversible Humidity-Responsive Phosphorescence Materials from Cellulose for Advanced Anti-Counterfeiting and Environmental Monitoring

Organic phosphorescence materials have many unique advantages, such as a large Stokes shift, high signal-to-noise ratio, and no interference from background fluorescence and scattered light. But, they generally lack responsiveness. Herein, we developed a new type of biopolymer-based phosphorescence materials with excellent processability and irreversible humidity-responsiveness, via introducing the imidazolium cation to cellulose chain. In the resultant cellulose derivatives, the imidazolium cation promotes the intersystem crossing, meanwhile the cation, chloride anion, and hydroxyl group form multiple hydrogen bonding interactions and electrostatic attraction interactions, which successfully inhibit the nonradiative transitions. As a result, the ionic cellulose derivatives exhibit green phosphorescence at room temperature and can be processed into phosphorescent films, coatings, and patterns. More interestingly, their phosphorescence emission changes when the different processing solvents are used. The ionic cellulose derivatives processed with acetone have a negligible phosphorescence, while they give an irreversible humidity-responsive phosphorescence, which means that the ionic cellulose derivatives processed with acetone exhibit significantly enhanced phosphorescence once they meet water vapor. Such novel irreversible responsive phosphorescence materials have huge potential in advanced anticounterfeiting, information encryption, molecular logic gates, smart tags, and process monitoring.

Structurally Nontraditional Bipolar Hosts for RGB Phosphorescent OLEDs: Boosted by a "Butterfly-Shaped" Medium-Ring Acceptor

The emitting layer based on a host-guest system plays a crucial role in organic light-emitting diodes (OLEDs). While emitters have witnessed rapid progress in structural diversity, hosts still rely heavily on traditional structures and are underdeveloped. Herein a "medium-ring" strategy has been put forward to design structurally nontraditional host molecules, which are not only rotatable enough to suppress close π-π stacking, thus reducing exciton annihilation, but also rigid enough to prevent excessive conformational flipping, thus inhibiting non-radiative decay. Accordingly, a brand-new type of bipolar hosts with a twisted "butterfly-shaped heptagonal acceptor (EtBP), which features an electron-deficient benzophenone fragment with a flexible ethylidene bridge, has been developed. With satisfactory morphological stability and well-balanced hole- and electron-transporting properties, the EtBP-based bipolar hosts enable high-performance RGB phosphorescent OLEDs with small efficiency roll-off, which are superior to those of acyclic benzophenone-based devices.

Three in One: Stimuli-Responsive Fluorescence, Solid-State Emission, and Dual-Organelle Imaging Using a Pyrene-Benzophenone Derivative

Small organic luminogens, owing to their contrasting stimuli-responsive fluorescence in solution along with strong emission in aggregated and solidstates, have been employed in optoelectronic devices, sensors, and bioimaging. Pyrene derivatives usually exhibit strong fluorescence and concentration-dependent excimer/aggregate emission in solution. However, the impacts of microenvironments on the monomer and aggregate emission bands and their relative intensities in solution, solid, and supramolecular aggregates are intriguing. The present study delineates a trade-off between the monomer and aggregate emissions of a pyrene-benzophenone derivative (ABzPy) in solution, in the solid-state, and in nanoaggregates through a combined spectroscopic and microscopic approach. The impact of external stimuli (viscosity, pH) on the aggregate emission was demonstrated using steady-state and time-resolved spectroscopy, including fluorescence correlation spectroscopy and fluorescence anisotropy decay analysis. The aggregate formation was noticed at a higher concentration (>10 μM) in solution, at 77 K (5 μM), and in the solid-state due to the π-π stacking interactions (3.6 Å) between two ABzPy molecules. In contrast, no aggregate formation was observed in the viscous medium as well as in a micellar environment even at a higher concentration of ABzPy (50 μM). The crystal structure analysis further shed light on the intermolecular hydrogen-bonding-assisted solid-state emission, which was found to be highly sensitive toward external stimuli like pH and mechanical forces. The broad emission band comprising both monomer and aggregate in the aqueous dispersion of nanoaggregates was used for the specific cellular imaging of lysosomes and lipid droplets, respectively.

Tunable Second-Level Room-Temperature Phosphorescence of Solid Supramolecules between Acrylamide-Phenylpyridium Copolymers and Cucurbit[7]uril

A series of solid supramolecules based on acrylamide-phenylpyridium copolymers with various substituent groups (P-R: R=-CN, -CO₂ Et, -Me, -CF₃ ) and cucurbit[7]uril (CB[7]) are constructed to exhibit tunable second-level (from 0.9 s to 2.2 s) room-temperature phosphorescence (RTP) in the amorphous state. Compared with other solid supramolecules P-R/CB[7] (R=-CN, -CO₂ Et, -Me), P-CF₃ /CB[7] displays the longest lifetime (2.2 s), which is probably attributed to the fluorophilic interaction of cucurbiturils leading to a uncommon host-guest interaction between 4-phenylpyridium with -CF₃ and CB[7]. Furthermore, the RTP solid supramolecular assembly (donors) can further react with organic dyes Eosin Y or SR101 (acceptors) to form ternary supramolecular systems featuring ultralong phosphorescence energy transfer (PpET) and visible delayed fluorescence (yellow for EY at 568 nm and red for SR101 at 620 nm). Significantly, the ultralong multicolor PpET supramolecular assembly can be further applied in fields of anti-counterfeiting and information encryption and painting.

Spin-orbital coupling and slow phonon effects enabled persistent photoluminescence in organic crystal under isomer doping

When periodically packing the intramolecular donor-acceptor structures to form ferroelectric-like lattice identified by second harmonic generation, our CD49 molecular crystal shows long-wavelength persistent photoluminescence peaked at 542 nm with the lifetime of 0.43 s, in addition to the short-wavelength prompt photoluminescence peaked at 363 nm with the lifetime of 0.45 ns. Interestingly, the long-wavelength persistent photoluminescence demonstrates magnetic field effects, showing as crystalline intermolecular charge-transfer excitons with singlet spin characteristics formed within ferroelectric-like lattice based on internal minority/majority carrier-balancing mechanism activated by isomer doping effects towards increasing electron-hole pairing probability. Our photoinduced Raman spectroscopy reveals the unusual slow relaxation of photoexcited lattice vibrations, indicating slow phonon effects occurring in ferroelectric-like lattice. Here, we show that crystalline intermolecular charge-transfer excitons are interacted with ferroelectric-like lattice, leading to exciton-lattice coupling within periodically packed intramolecular donor-acceptor structures to evolve ultralong-lived crystalline light-emitting states through slow phonon effects in ferroelectric light-emitting organic crystal.