High Phosphorescence Quantum Yield Research Articles

Ultrafast dynamics of mCP and Br-mCP: Insights from transient absorption spectroscopy

Heavy atom activated organic room-temperature phosphorescence (RTP) has attracted considerable interest due to its high phosphorescence quantum yield and prolonged lifetime. This research provides a detailed analysis of the transient absorption spectroscopy of 1,3-Bis(N-carbazolyl)benzene (mCP) and 9,9'-(5-Bromo-1,3-phenylene)bis(9H-carbazole) (Br-mCP) in toluene solution. In the femtosecond transient absorption (fs-TA) spectroscopy of mCP, the excited state absorption (ESA) signal decreases at 630 nm while the triplet-triplet absorption (TTA) signal increases at 420 nm. Meanwhile, the isosbestic point observed at 455 nm indicates an intersystem crossing (ISC) lifetime of 15.4 ns. Moving on to the nanosecond transient absorption (ns-TA) spectroscopy, the TTA signal reaches its peak at 27.3 ns before decreasing, with the triplet lifetime of mCP measured at 2.8 μs. Br-mCP exhibits a similar dynamic evolution to mCP, but with a quicker ISC process (9.4 ns) and a longer triplet lifetime (3.9 μs). The quicker ISC process in Br-mCP is ascribed to the presence of heavy atom in the molecular structure, leading to an enhanced spin-orbit coupling constant (ξ(S1, T3)Br-mCP = 1.371 cm-1 > ξ(S1, T4)mCP = 0.060 cm-1). The prolonged triplet lifetime of Br-mCP (3.9 μs > 2.8 μs) results from its lower reorganization energy, effectively reducing non-radiative vibrational energy losses within the molecule. This work significantly enhances our understanding of RTP materials incorporating heavy atoms.

Enabling efficient and ultralong room-temperature phosphorescence from organic luminogens by locking the molecular conformation in polymer matrix

Tackling the challenge of developing ultralong organic phosphorescence (UOP) materials with a high phosphorescence quantum yield (Φphos.) and an ultralong phosphorescence lifetime (τphos.) under ambient conditions is urgently needed. Herein, typical organic luminogens with simple chemical structures, namely, triphenylamine (TPA), 9-phenylcarbazole (PCz), and indolo[3,2,1-jk]carbazole (ICz), are doped into a melamine–formaldehyde (MF) polymer matrix with a compact three-dimensional covalent network to prepare UOP materials, respectively. Both experiments and theoretical calculations suggest that restricting intramolecular motions to suppress the nonradiative decay of triplet excitons plays a critical role in achieving ultralong room-temperature phosphorescence from organic molecules in polymer matrices. The luminophore ICz with a planar and rigid chemical structure, constructed by locking the molecular conformation of TPA via carbon–carbon single bonds, exhibits a bright organic afterglow with a Φphos. up to 38.31 % and a τphos. up to 2.73 s in the MF polymer under ambient conditions, representing one of the most excellent polymer-based organic afterglow materials in comprehensive UOP performance. The gradual enhancement in UOP of the resulting luminescent materials has led to their successful use in multi-level anti-counterfeiting. This work provides an effective strategy for developing organic afterglow materials with both high Φphos. and τphos. values.

Construction of Binary Matrix for Efficient Room Temperature Phosphorescence Emission

AbstractDespite the extensive research on room temperature phosphorescent (RTP) materials, it remains a great challenge to further improve the photophysical properties of RTP materials. In this study, the RTP emission of guest molecule is significantly enhanced by constructing binary matrices containing cyanuric acid (CA) and amino‐containing compounds. Systematic studies show that the strong interaction between the two components of binary matrix induced variations in the guest molecular configuration and excited state electron distribution, thus facilitating the production of more triplet excitons. Furthermore, the binary matrix also exhibits stronger domain‐limiting effect compared to the CA mono‐matrix, effectively inhibits the energy loss of triplet excitons due to quenching and non‐radiative transitions. The prepared binary matrix RTP materials present ultralong phosphorescence lifetime and high phosphorescence quantum yield (up to 3.21 s and 7.31%, respectively), and even achieve bright RTP emission in a variety of organic solvents and aqueous media. Moreover, the RTP emission intensity of the best binary matrix composite can reach more than 28 times that of the CA mono‐matrix composite, and the RTP lifetime can be extended by 1.51 s.

A co-doping strategy to fabricate ultralong organic room temperature phosphorescence (ORTP) materials: Designing, preparation and advanced applications

Isophthalic acid (IPA) is a star phosphorescence molecule, which is a commercially available raw material with simple chemical structure, but is of good phosphorescence performance. However, the great research vacancy is still maintained because of its limited applications. Absolutely, polymer-matrix strategy is a common method to produce phosphorescence amorphous material by dispersing IPA into matrix such as polyvinyl alcohol (PVA). But how to further optimize the phosphorescence property of the resulted doping material (PVA-IPA)? Up to now, this question is new and very little attention has been paid. In this work, a co-doping strategy was explored, that is, charging the second dopant of ClCH2COOH into PVA-IPA was verified as a promising method to further enhance the phosphorescence property of PVA-IPA, leading to the co-doping material PVA-IPA-ClCH2COOH with ultralong phosphorescence lifetime as 500 ms and high phosphorescence quantum yield (ΦP) as 23.7%. Depending on these promising phosphorescence behaviors, PVA-IPA-ClCH2COOH was successfully applied in the fields of information anti-counterfeiting and artificial light harvest.

Directed Chiral Self‐Assembly of Purely Organic Phosphors for Room‐Temperature Circularly Polarized Phosphorescence

AbstractCircularly polarized phosphorescence (CPP) is increasingly recognized in materials science for its unique applications in optoelectronic devices, chiral recognition, and bioimaging. This study underscores a novel directed chiral self‐assembly strategy of purely organic phosphors into supramolecular nanostructures to achieve bright room‐temperature circularly polarized phosphorescence (RT‐CPP). RT‐CPP molecules are built on an aromatic carbonyl structure having also Br to mix (n,π*) and (π,π*) characters and to enable the heavy atom effect. Side chains are rationally designed to have strong hydrogen bonding, van der Waals interactions, and a chiral center for directed chiral self‐assembly into supramolecular nanostructures. The tightly packed resulting supramolecular nanostructures also impower efficient suppression of molecular motions, thereby minimizing non‐radiative decay and facilitating bright CPP emission at room temperature. The developed self‐assembled supramolecular structures exhibit RT‐CPP with the dissymmetry factor (glum) of ≈10−3, a high phosphorescence quantum yield of 4.1%, and a rapid triplet decay time of 180 microseconds. The presented molecular design principle enabling RT‐CPP from purely organic phosphors may pave the way for novel photonic materials.

Multiemitting Ultralong Phosphorescent Carbonized Polymer Dots via Synergistic Enhancement Structure Design.

Advancing a metal-free room temperature phosphorescent (RTP) material that exhibits multicolor emission, remarkable RTP lifetime, and high quantum yield still faces the challenge of achieving intersystem crossing between singly and triplet excited states, as well as the rapid decay of triplet excited states due to nonradiative losses. In this study, a novel strategy is proposed to address these limitations by incorporating o-phenylenediamine, which generates multiple luminescent centers, and long-chain polyacrylic acid to synthesize carbonized polymer dots (CPDs). These CPDs are then embedded in a rigid B2O3 matrix, effectively limiting nonradiative losses through the synergistic effects of polymer cross-linking and the rigid matrix. The resulting CPD-based materials exhibit remarkable ultralong phosphorescence in shades of blue and lime green, with a visible lifetime of up to 49 s and a high phosphorescence quantum yield. Simultaneously, this study demonstrates the practical applicability of these excellent material properties in anti-counterfeiting and information encryption.

Spin-Vibronic Intersystem Crossing and Molecular Packing Effects in Heavy Atom Free Organic Phosphor.

We present a detailed investigation into the excited state properties of a planar D3h symmetric azatriangulenetrione, HTANGO, which has received significant interest due to its high solid-state phosphorescence quantum yield and therefore potential as an organic room temperature phosphorescent (ORTP) dye. Using a model linear vibronic coupling Hamiltonian in combination with quantum dynamics simulations, we observe that intersystem crossing (ISC) in HTANGO occurs with a rate of ∼1010 s-1, comparable to benzophenone, an archetypal molecule for fast ISC in heavy metal free molecules. Our simulations demonstrate that the mechanism for fast ISC is associated with the high density of excited triplet states which lie in close proximity to the lowest singlet states, offering multiple channels into the triplet manifold facilitating rapid population transfer. Finally, to rationalize the solid-state emission properties, we use quantum chemistry to investigate the excited state surfaces of the HTANGO dimer, highlighting the influence and importance of the rotational alignment between the two HTANGO molecules in the solid state and how this contributes to high phosphorescence quantum yield.

Multi‐Color Pure Organic Room Temperature Phosphorescent Materials with Long Lifetime and High Efficiency

AbstractOrganic room temperature phosphorescent (ORTP) materials have garnered significant interest in the fields of anti‐counterfeiting, optical display, and bio‐imaging owing to their distinctive optical properties. However, a major drawback of most existing ORTP materials is their short phosphorescence lifetime and low quantum yields (QYs), which greatly limit their applicability across multiple fields. In this paper, a covalently assisted host‐guest doping strategy that involves embedding three aminobenzoic acids with different carboxylate substitution positions into a cyanuric acid (CA) matrix through covalent bonding using microwave heating is proposed. All three prepared ORTP materials exhibit long phosphorescence lifetime exceeding 600 ms and high phosphorescence quantum yields (PhQYs) surpassing 20%. Among them, the composite of 2‐aminoterephthalic acid (2‐A) anuric acid stands out with its unique blue phosphorescence, boasting an exceptional absolute photoluminescence quantum yield (PLQY) of 98.95% and remarkable phosphorescence quantum yield (PhQY) of 76.42%, along with a long lifetime of 800 ms. Importantly, these high‐performance ORTP materials have been successfully utilized in anti‐counterfeiting and display applications.

Colorful Ultralong Room Temperature Phosphorescent Afterglow with Excitation Wavelength Dependence Based on Boric Acid Matrix

AbstractRoom temperature phosphorescent (RTP) materials have triggered wide interests because of their excellent performance and various promising applications. However, conventional RTP materials possessing color‐tunable and ultralong afterglow often suffer from low phosphorescent emission efficiency. Herein, a long lifetime and high‐efficiency RTP emission system composed of boric acid as the host matrix and organic phosphors as guest molecules is constructed by suppressing the non‐radiative transition process and promoting the triplet exciton of the phosphors. The synergistic effect of the physically limited domain and supramolecular anchoring also contributes to the ultralong lifetime (up to 1.85 s) and high phosphorescence quantum yield (up to 53%). The afterglow can be visually observed for 30 s. With a large overlap of π‐conjugated chromophores, the emission peak of RTP redshifted, realizing cyan, green, and red afterglow in the monochromatic domain. In addition, the emission of colorful afterglow and white afterglow is adjustable with the different co‐doping ratios. Finally, the application of RTP materials to anti‐counterfeiting encryption is demonstrated.

Controllable Ultralong Phosphorescence through Substituent Modulation for Dynamic Anti‐Counterfeiting

AbstractThe development of highly stable and ultra‐long organic room temperature phosphorescence (RTP) materials holds great promise for applications in anti‐counterfeiting and information protection. To improve the encryption level, the exploration of organic materials with tunable phosphorescence and afterglow features is in urgent need. Hereby, a series of long‐lived organic systems with RTP is developed by incorporating benzocarbazole derivatives into a polyvinyl alcohol (PVA) matrix (BCz@PVA). Notably, the BCz@PVA film exhibits outstanding RTP behavior with an ultralong phosphorescence lifetime (τp) of 2.09 s, high phosphorescence quantum yield (Φp) of 46.335%, and an ultra‐long afterglow duration of 15 s. Moreover, the BCz@PVA film maintains excellent RTP performance even after being placed in ambient conditions for 60 days. Theoretical calculations reveal that the excellent RTP performance of BCz@PVA film is attributed to the stronger intermolecular interactions, the smaller energy gap (ΔEst) between the singlet and triplet states, and stable molecular stacking mode. Furthermore, color‐tunable photoluminescence (PL), distinct τp, and afterglow duration are successfully achieved by adjusting the position of the Br substituent on the benzene ring. Based on their diverse RTP performances and excellent stability, the corresponding BCz@PVA film provides successful application for multi‐level high‐security anti‐counterfeiting and information protection.

Pyrolysis of Al-Based Metal-Organic Frameworks to Carbon Dot-Porous Al2 O3 Composites With Time-Dependent Phosphorescence Colors for Advanced Information Encryption.

Phosphorescent materials with time-dependent phosphorescence colors (TDPCs) have great potential in advanced optical applications. Synthesis of such materials is attractive but challenging. Here, a series of carbon dot-porous Al2 O3 composites exhibiting distinctive TDPC characteristics is prepared by high-temperature pyrolysis of Al-based metal-organic frameworks NH2 -MIL-101(Al). The composite synthesized at 700 °C (CDs@Al2 O3 -700) shows an obvious change in phosphorescence color from blue to green after removing the excitation light of 280nm. Photophysical analysis reveals that two emission centers in CDs, namely carbon core and surface states, are responsible for the short-lived blue phosphorescence (96ms) and long-lived green phosphorescence (911ms), respectively. The combination of blue and green phosphorescence with different decay rates triggering the interesting TDPC phenomenon. CDs@Al2 O3 -700 has a significantly high phosphorescence quantum yield of up to 41.7% and possesses an excellent optical stability against water, organic solvents, and strong oxidants, which benefits from the multi-confinement of CDs by the porous Al2 O3 matrix through rigid network, strong space constraint, and stable covalent bonding. Based on the TDPC property, multilevel coding patterns composed of CDs@Al2 O3 are successfully fabricated for advanced dynamic information encryption.

Radioluminescent Cu-Au Metal Nanoclusters: Synthesis and Self-Assembly for Efficient X-ray Scintillation and Imaging.

Zero-dimensional (0D) scintillation materials have drawn tremendous attention due to their inherent advantages in the fabrication of flexible high-energy radiation scintillation screens by solution processes. Although considerable progress has been made in the development of 0D scintillators, such as the current leading lead-halide perovskite nanocrystals and quantum dots, challenges still persist, including potential issues with self-absorption, air stability, and eco-friendliness. Here, we present a strategy to overcome those limitations by synthesis and self-assembly of a new class of scintillators based on metal nanoclusters. We demonstrate the gram-scale synthesis of an atomically precise nanocluster with a Cu-Au alloy core exhibiting high phosphorescence quantum yield, aggregation-induced emission enhancement (AIEE) behavior, and intense radioluminescence. By controlling solvent interactions, the AIEE-active nanoclusters were self-assembled into submicron spherical superparticles in solution, which we exploited as a novel building block for flexible particle-deposited scintillation films with high-resolution X-ray imaging performance. This work reveals metal nanoclusters and their self-assembled superstructures as a promising class of scintillators for practical applications in high-energy radiation detection and imaging.

Microemulsion-Based Fabrication of Organic Nanocrystals for Persistent Phosphorescence Bioimaging

Persistent phosphorescence eliminates the need for light excitation and thus avoids the issue of autofluorescence, holding great promise in various fields. To achieve bright phosphorescence emission, many methods were developed to confine most organic persistent phosphorescent materials in a rigid environment aiming to quench nonradiative relaxation pathways; among them, the nanocrystal method is a good candidate which can rigidify the molecules as well as offer the desirable water dispersity and size for further bioapplications. However, the current efficient preparation of phosphorescent nanocrystals still remains challenging. This study reports an efficient microemulsion-based method for the fabrication of phosphorescent nanocrystals with a desired diameter in the nanosize range (below 200 nm), a high phosphorescence quantum yield of about 6.5%, and ultralong persistent phosphorescence to the timescale after the removal of the external light source, making it easy for the commercial imaging system to detect, which is suitable for practical bioimaging. Furthermore, the synthesized nanocrystals with biocompatibility were utilized directly for in vitro imaging, showing effective cellular uptake and bright phosphorescence emission, which provides a reasonable strategy to develop a phosphorescent nanocrystal for application.

Photodynamics of the Molecular Ruby [Cr(ddpd)2]3.

The introduction of strong-field ligands can enable luminescence in first-row transition-metal complexes. In this way, earth-abundant near-infrared emitters can be obtained using early 3d metals. A prime example is the molecular ruby [Cr(ddpd)2]3+ (ddpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine) that can achieve high phosphorescence quantum yields at room temperature in aqueous solution. To understand these remarkable properties, here, we simulate its photodynamics in water using trajectory surface hopping on linear vibronic coupling potentials parametrized from multiconfigurational CASSCF/CASPT2 calculations. We find that after excitation to the second absorption band, a relaxation cascade through metal-centered states occurs. After an initial back-and-forth intersystem crossing with higher-lying doublet states, the complex relaxes through a manifold of quartet metal-centered states to the low-lying doublet metal-centered states which are responsible for the experimentally observed emission. These electronic processes are driven by an elongation of the Cr-ligand bond lengths as well as the twisting motion of the trans-coordinated pyridine units in the ddpd ligands. The low-lying doublet states are reached within 1-2 ps and are close in geometry to the doublet minima, thus explaining the high phosphorescence quantum yield of the molecular ruby [Cr(ddpd)2]3+.

Ultralong Room-Temperature Phosphorescence of Boron Carbon Oxynitride Nanodots Encapsulated in Pyrophosphate in Dry and Wet States for Fingerprint Detection and Information Protection

Room-temperature phosphorescence (RTP) materials have attracted wide interest due to their long lifetime and free from background autofluorescence. Nevertheless, simultaneous activation of stable long-lived RTP emission in both solid and aqueous phases remains a tremendous challenge. Herein, a molten salt method to synthesize boron carbon oxynitride nanodot-based RTP composites (BCNO nanodots@pyrophosphate) was carried out by employing pyrophosphate as the inert shell for BCNO nanodots. The BCNO nanodots@pyrophosphate1 with the average size of 3.69 nm show bright-green RTP because the introduction of phosphorus is beneficial to the intersystem crossing process and increases the RTP emission. What is more, whether in solid or aqueous dispersion, BCNO nanodots@pyrophosphate1 retains good phosphorescent properties with a high phosphorescence quantum yield (29.5% and 18.6%) and a long lifetime (1.39 and 1.29 s), which lasts over 15 s to the naked eye. This is the first report on BCNO nanodots with RTP in aqueous solution. The unique RTP characteristics allow BCNO nanodots@pyrophosphate as a hopeful indicator for detection of latent fingerprints with high contrast and multilevel information protection.

New Phthalic Anhydride‐Based Room‐Temperature Phosphorescence Emitter with Lifetime Longer Than One Second

AbstractOrganic room‐temperature phosphorescence (RTP) materials have attracted much attention in recent years due to their potential applications. However, the development of organic RTP emitters with a long lifetime and high quantum yield remains a great challenge owing to the weak molecular spin–orbit coupling and high sensitivity to oxygen. In this paper, a new purely organic RTP emitter, 3,3″,4,4″‐diphenylsulfonetetracarboxylic dianhydride (DPS), is reported which shows an excitingly ultralong lifetime up to 1.08 s and high phosphorescence quantum yield of 8%. When anhydride units in DPS are transformed into imides, the RTP performance in terms of lifetime and quantum yield is decreased. The presence of multiple intermolecular interactions is favorable for the restriction of nonradiative decay and the promotion of spin–orbit coupling, which is further corroborated by theoretical calculations. The studies demonstrate that DPS is a promising structural motif for developing high‐performance organic RTP emitters.

Organic Phosphorescence Lasing Based on a Thermally Activated Delayed Fluorescence Emitter.

Organic phosphorescence materials provide an opportunity to use triplets for lasing. However, population inversion based on phosphorescence is hard to establish, owing to low luminescent quantum efficiency and intensive optical loss. By comparison, thermally activated delayed fluorescence emitters exhibit excellent optical gain with the aid of the reverse intersystem crossing (RISC) process. In this work, we designed a multifunctional gain material, not only serving as a thermally activated delayed fluorescence (TADF) emitter with excellent optical gain but also working as a phosphorescence source with high utilization of triplets. The lone pair of electrons in oxygen substitutions promotes a fast spin-flip and high delayed fluorescence quantum yield (ΦDF = 55%), enabling TADF amplified spontaneous emissions (ASE) of CH2Cl2 solution. Single-crystalline nanowires of H-aggregates effectively lower triplet energy levels with high phosphorescence quantum yield (ΦP = 27%), demonstrating Fabry-Perot mode phosphorescence lasing at 630 nm.

Distinguishing the Quantum Yield and Lifetime of Carbazole‐Based Room‐Temperature Phosphorescence Materials: QM/MM Study

AbstractCommercial carbazole derivatives are widely used as typical electron donors in room‐temperature phosphorescence materials. The high phosphorescence quantum yield (Φp) and short lifetime (τp) of the carbazole‐based (9H‐carbazol‐9‐yl)isonicotinonitrile (P‐34N) crystal are distinguished by quantum mechanics and molecular mechanics method. Two inducements are accounted for the high Φp of P‐34N: i) large spin–orbit coupling (0.63 cm−1) induces fast intersystem crossing (ISC) of the lowest singlet excited state (S1) to the lowest triplet excited state (T1), ii) the intermolecular π–π interactions stabilize triplet excitons. Meanwhile, the 3(n, π*) →1(π, π*) of P‐34N favors the nonradiative decay of T1to the ground state (S0), and thus, causes short τp. In contrast to P‐34N, the low Φp of 6‐(9H‐carbazol‐9‐yl)nicotinonitrile (P‐24N) crystal results from the effective reverse ISC process induced by small ΔEST (0.3 eV) between S1 state and the higher triplet state (T2), and the long τp is due to the unfavorable orbital reversals of T1 (π, π*)→S0 (π, π*) transition and the internal conversion process of T2 → T1. This work presents a reasonable interpretation of the Φp and τp of two carbazole‐based crystals.

Achieving Color‐Tunable and Time‐Dependent Organic Long Persistent Luminescence via Phosphorescence Energy Transfer for Advanced Anti‐Counterfeiting

AbstractOrganic ultralong room‐temperature phosphorescence (RTP) materials have promising applications in anti‐counterfeiting. To improve the encryption level, the exploration of organic materials with tunable solid‐state long persistent luminescence is in urgent need. Herein, a series of organic ultralong RTP polymeric systems are prepared by doping versatile indolocarbazole isomers into the poly(vinyl alcohol) (PVA) matrix. Notably, the doping film 11,12‐ICz@PVA exhibits excellent RTP property with an ultralong lifetime of 2.04 s and a high phosphorescence quantum yield of 44.1%. Theoretical calculations reveal that this excellent RTP property can be attributed to the strong electrostatic attraction resulting from the synergistic double hydrogen‐bond between the isomer 11,12‐ICz and PVA matrix. More impressively, color‐tunable and time‐dependent long persistent luminescence is successfully achieved through efficient phosphorescence energy transfer between the indolocarbazole isomers with ultralong blue RTP emissions and commercially available fluorescent dyes with emission colors ranging from green to red doped into the PVA matrix. Besides, diversified encryption patterns are fabricated to demonstrate the promising applications of these water‐soluble doping PVA systems with tunable solid‐state persistent luminescence in advanced anti‐counterfeiting technology.

Efficient room-temperature phosphorescence of covalent organic frameworks through covalent halogen doping.

Organic room-temperature phosphorescence, a spin-forbidden radiative process, has emerged as an interesting but rare phenomenon with multiple potential applications in optoelectronic devices, biosensing and anticounterfeiting. Covalent organic frameworks (COFs) with accessible nanoscale porosity and precisely engineered topology can offer unique benefits in the design of phosphorescent materials, but these are presently unexplored. Here, we report an approach of covalent doping, whereby a COF is synthesized by copolymerization of halogenated and unsubstituted phenyldiboronic acids, allowing for random distribution of functionalized units at varying ratios, yielding highly phosphorescent COFs. Such controlled halogen doping enhances the intersystem crossing while minimizing triplet-triplet annihilation by diluting the phosphors. The rigidity of the COF suppresses vibrational relaxation and allows a high phosphorescence quantum yield (ΦPhos ≤ 29%) at room temperature. The permanent porosity of the COFs and the combination of the singlet and triplet emitting channels enable a highly efficient COF-based oxygen sensor, with an ultra-wide dynamic detection range (~103-10-5 torr of partial oxygen pressure).