Efficient Phosphorescence Research Articles

The Effect of Monodentate Co-Ligands on the Properties of Pt(II) Complexes Bearing a Tridentate C^N*N-Luminophore

In this study, the insertion of different monodentate co-ligands on Pt(II) complexes bearing a monoanionic C^N*N luminophore as a tridentate chelator was achieved beyond the previously reported chlorido- ([PtCl(L)]) and cyanido-decorated ([PtCN(L)]) analogues. To investigate the impact of the auxiliary ligand on the photophysical properties, we introduced a neutral carbonyl-ligand and observed a lower photoluminescence quantum yield (ΦL) than with a cyanido moiety. However, the direct substitution of the chlorido co-ligand by a NO-related derivative was not successful. Interestingly, the attempted reduction of the successfully inserted nitrito-N-ligand in [PtNO2(L)] resulted in the oxidation of the Pt(II)-center to Pt(IV), as demonstrated by X-ray diffractometry. For comparison, the trifluoroacetato Pt(II) and chlorido Pt(IV) complexes ([PtTFA(L)] and [PtCl3(L)], respectively) were also synthesized. The photophysical characterization revealed similar photoluminescence profiles for all complexes, indicating a weak effect of the co-ligand on the excited state; in fact, all complexes display emission from metal-perturbed ligand-centered states (even the Pt(IV) species). Nonetheless, longer excited state lifetimes (τav) suggest a reduced thermally-activated radiationless deactivation via metal-centered states upon exchange of the chlorido units for other monodentate entities, yet without significantly improving the overall ΦL at room temperature. The irreversible oxidation waves (measured via cyclic voltammetry) mostly stem from the Pt(II)-center; the co-ligand-related drop of these potentials correlates with the increasing σ-donating capacities of the ancillary ligand. In summary, an enhanced π-acceptor capacity does not necessarily improve the ΦL and can even impair radiative rates by compromising the perturbative participation of the metal center on the emissive triplet state; in addition, strong σ-donor abilities improve the phosphorescence efficiencies by hampering the thermal population of dissociative electronic configurations related to the participation of antibonding d*-orbitals at the metal center.

Selenoxanthen-9-one-based emitters exhibiting efficient room temperature phosphorescence for electroluminescent and oxygen sensing applications

Two selenoxanthen-9-one-based emitters (Se-2DPA and Se-2TPA) were synthesized by introducing diphenylamine and triphenylamine as electron donors. The doped films of Se-2DPA and Se-2TPA exhibited bright fluorescence-phosphorescence dual emission and comparable photoluminescence quantum yields (ΦPL) of 31.4 % and 29.6 %, respectively. Unlike the Se-2DPA with phosphorescence lifetime of 1.1 ms, Se-2TPA shows significantly extended phosphorescence lifetime up to 17.7 ms. As revealed by computational and experimental investigations, Se-2DPA maintained more effective spin orbit coupling (SOC) between T1 and S0 states and its radiative rate constant of phosphorescence is 1 order of magnitude higher than that of Se-2TPA, which resulted in a relatively shorter phosphorescence lifetime. Consequently, solution-processed organic light-emitting diodes (OLEDs) based on Se-2DPA with shorter phosphorescence lifetime achieved a maximum external quantum efficiency of 8.8 %, which is much higher than the device based on Se-2TPA (only 0.8 %). In contrast, Se-2TPA showed higher sensitivity for oxygen sensing and the Stern-Volmer quenching constant (KSV) value reached 3.04 × 10−3 ppm owing to the longer phosphorescence lifetime, which is over 3-folds higher than that of Se-2DPA (8.88 × 10−4 ppm) under the same conditions.

Single-Molecular White Emission of Organic Thianthrene-Based Luminophores Exhibiting Efficient Fluorescence and Room Temperature Phosphorescence Induced by Halogen Atoms

Single-Molecular White Emission of Organic Thianthrene-Based Luminophores Exhibiting Efficient Fluorescence and Room Temperature Phosphorescence Induced by Halogen Atoms

High‐Brightness, Hundred‐Second Level Ultralong Afterglow Polymers Built via Ultrasound‐Synchronized B‐O‐Click Strategy

AbstractIn recent years, there has been a growing interest in pure organic materials with ultralong room temperature phosphorescence (RTP) and afterglow duration time (tag) in the range of second level. However, it is extremely difficult to achieve tag >60 s in the polymer fields. Herein, this work proposes a highly versatile ultrasound‐synchronized B‐O‐Click strategy that can firmly immobilize various types of polycyclic aromatic boronic acids (PABAs) as single‐molecular states in a tight and rigid matrix of poly(vinyl alcohol) (PVA), achieving a series of record‐breaking ultralong afterglow polymeric RTP materials. Based on this approach, a polymeric material is reported exhibiting a record‐breaking tag = 130 s, accompanied with an ultralong lifetime of 7.24 s and a good phosphorescence efficiency of 14.26%. Three other polymeric materials with tag over 60 s are also realized via the same strategy by changing the phosphor. In addition, record‐breaking ultralong green (tag = 115 s) and red (tag = 80 s) afterglow are further achieved based on the phosphorescence resonance energy transfer (PRET) effect.

Naphthyl Substituted Impurities Induce Efficient Room Temperature Phosphorescence

AbstractAccidentally, it was found that triphenylamine (TPA) from commercial sources shows ultralong yellow‐green room temperature phosphorescence (RTP) like commercial carbazole, which however disappears for lab‐synthesized TPA with high purity. Herein, we for the first time identify the impurity types that cause RTP of commercial TPA, which are two N, N‐diphenyl‐naphthylamine isomers. Due to similar molecular polarity and very trace amount (≈0.8 ‰, molar ratio), these naphthyl substituted impurities can be easily overlooked. We further show that even at an extremely low amount (1000000 : 1, mass ratio) of impurities, RTP emission is still generated, attributed to the triplet‐to‐triplet energy transfer mechanism. Notably, this doping strategy is also applicable to the triphenylphosphine and benzophenone host systems, of which strong RTP emission can be activated by simply doping the corresponding naphthyl substituted analogues into them. This work therefore provides a general and efficient host/guest strategy toward high performance and diverse organic RTP materials.

Naphthyl Substituted Impurities Induce Efficient Room Temperature Phosphorescence.

Accidentally, it was found that triphenylamine (TPA) from commercial sources shows ultralong yellow-green room temperature phosphorescence (RTP) like commercial carbazole, which however disappears for lab-synthesized TPA with high purity. Herein, we for the first time identify the impurity types that cause RTP of commercial TPA, which are two N, N-diphenyl-naphthylamine isomers. Due to similar molecular polarity and very trace amount (≈0.8 ‰, molar ratio), these naphthyl substituted impurities can be easily overlooked. We further show that even at an extremely low amount (1000000 : 1, mass ratio) of impurities, RTP emission is still generated, attributed to the triplet-to-triplet energy transfer mechanism. Notably, this doping strategy is also applicable to the triphenylphosphine and benzophenone host systems, of which strong RTP emission can be activated by simply doping the corresponding naphthyl substituted analogues into them. This work therefore provides a general and efficient host/guest strategy toward high performance and diverse organic RTP materials.

Reblooming of the cis-Bis(2-phenylpyridine) Platinum(II) Complex: Synthesis Updating, Aggregation-Induced Emission, Electroluminescence, and Cell Imaging.

Studies on the syntheses, photophysical properties, and applications of cis-bis(2-phenylpyridine) platinum(II) complex (Pt(ppy)2) family are of great importance, but very limited progress has been achieved to date. Herein, a one-pot method was established for the syntheses of Pt(ppy)2-type complexes Pt-ppy and Pt-tBu. These two compounds were nonemissive in dilute solutions. However, they produced intense red and deep-red phosphorescence in the aggregation and film states, with lifetimes and quantum yields up to 1.92 μs and 70%, respectively, exhibiting unique aggregation-induced emission (AIE) characteristics. According to the experimental and theoretical studies, molecular configuration transformation (MCT) in the excited state may occur because of the d-d transition from the Pt center, causing nonradiative transitions in the solution. Nevertheless, the MCT would be largely restricted by the intermolecular interactions or rigid matrix, thereby enabling efficient phosphorescence in the aggregation state and in the PMMA films. Consequently, the AIE characteristics of Pt-ppy and Pt-tBu probably result from the restriction of molecular configuration transformation (RMCT). Due to the π-π and/or weak Pt-Pt interactions and the concentration-dependent emission characteristics, they emit deep-red and NIR emissions generated by excimer and/or MMLCT emitting species. Inspired by their AIE features, electroluminescence and cell imaging applications are explored. To the best of our knowledge, this is the first comprehensive study on the synthesis optimization, photophysical properties, AIE characteristics, and applications of the Pt(ppy)2-type complexes, which may rebloom the research studies on this type of Pt(II) complex family and provide valuable insights on the development of phosphorescent AIE metal-organic complexes.

Achieving efficient room temperature phosphorescence of 1, 8-naphthalimide by a three-component doping strategy

Yellow phosphorescence emission of 1,8-naphthalimide guest was activated by doping it into m-bromobenzaldehyde host (energy transfer mechanism). With the aim of alleviating the triplet-triplet annihilation of the benzaldehyde itself, m-dibromobenzene was introduced as the third component. As a result, the phosphorescence quantum yields of the doped crystallized materials significantly increase from 1.72 % for NI@mBA to 19.17 % for NI@mBA@mDBB (with 11 times enhancement) due to the cascade activation in the three-component system. The encryption/decryption using these phosphorescent doped materials provides potential application in security field. This study not only expands the scope of organic host molecules capable of activating the phosphorescence properties of NI, but also provides a platform for developing multi-component organic doping systems that can effectively regulate phosphorescence properties.

Evaluating the Phosphorescence duration of Zn2P2O7 glass–ceramic activated by Dy3+/Pr3+ for LED applications

The present study focuses on investigating the phosphorescence efficiency of binary zinc–phosphate glasses co-doped with dysprosium and/or praseodymium oxides together with their corresponding glass ceramics. The studied glass series was prepared directly by the conventional melting and quenching method. Differential thermal analysis (DTA) indicated an exothermic peak at 550 °C that was applied to yield glass-ceramic samples. The major monoclinic phase of Zn2P2O7 was detected by X-ray diffraction (XRD). FTIR and SEM–EDAX were applied to identify the structural morphology of the prepared samples. The optical efficiency was characterized through UV–Visible–NIR absorption spectra and photoluminescence analysis. Both light emissions and their corresponding lifetimes were enhanced significantly in glass–ceramic. These samples display high CRI, low color temperature, and CIE values comparable to those expected for pure white-light and warm yellow emitting diodes.

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.

High-Quality Circularly Polarized Organic Afterglow from Nonconjugated Amorphous Chiral Copolymers.

Organic materials featuring circularly polarized luminescence (CPL) and/or afterglow emission represent an active research frontier with promising applications in various fields, but the achievement of high-performance CPL organic afterglow (CPOA) remains a huge challenge due to the intrinsic contradictions between the luminescent lifetime/dissymmetry factor (glum) and phosphorescent quantum efficiency (PhQY). Herein, we report a simple and universal approach to design efficient CPOA from amorphous copolymers by incorporating chiral chromophores into a nonconjugated clusterization-triggered emissive polymer with plenty of hydron-bonding interactions, followed by aggregation engineering using water dissolution and evaporation. With this chiral copolymerization and aggregation engineering (CCAE) strategy, high-performance CPOA polymers with PhQYs of up to 6.32%, ultralong lifetimes of over 650 ms, glum values of 3.54 × 10-3, and the highest figure-of-merit were achieved at room temperature. Given the impressive CPOA performance of these polymers, the applications in multilevel data anticounterfeiting and reversible displays with high stability were demonstrated. These findings through the CCAE strategy to overcome the inherent restraints of CPOA materials lay the foundation for the development of amorphous polymers with superior CPOA, significantly expanding the understanding of CPL and the design of organic afterglow materials.

Efficient room-temperature phosphorescence with tunable lifetime through light modulation from flexible polymer films

Photo-responsive materials (PRMs) featuring remarkable variation in emission color and/or intensity under light stimulus have attracted much attention due to their potential applications in information storage, anti-counterfeit and sensing. Herein, a new kind of PRMs with tunable luminescence lifetimes manipulated by light stimulus is reported. Transparent and flexible polymer films with room temperature phosphorescence (RTP) property are facilely prepared by solution blending polymers and chromophores. Not only RTP intensity, but also RTP lifetime of the doped polymer films is reversibly regulated through consecutive UV irradiation. Particularly, RTP lifetime is amendable between 0.83 and 2.84 s by facilely regulating irradiation duration, which is related to the consumption of oxygen in the polymer films. Taking advantage of the tunable RTP lifetime and intensity, the doped polymer films are used for rewritable write-once-read-many (WORM) information storage. In addition, application of the polymer films in visual sensing of environmental moisture is demonstrated. This work offers a new kind of PRMs with modulable emission lifetimes through light stimuli, which is useful for various applications including sensing, anti-counterfeiting and data storage.

Achieving Ultralong Room-Temperature Phosphorescence in Two-Dimensional Metal Halide Perovskites by Alkyl Chain Engineering.

Two-dimensional (2D) metal halide perovskites with highly efficient ultralong room-temperature phosphorescence (URTP) are rare due to their uncertain structures and complicated intermolecular interactions. Herein, by varying the alkyl length of organic units, we synthesized two single-component 2D metal hybrid perovskites, i.e., B-MACC and B-EACC, with obvious URTP emission. In particular, B-EACC exhibits a green-yellow URTP emission with an ultralong lifetime (579 ms) and a high efficiency (14.86%). It is found that the molecular packing of B-EA+ cations because of the presence one more carbon in the alkyl chain affords strong hydrogen bonding and π-π stacking interactions, which immobilizes and reduces the triplet exciton quenching. Moreover, B-MACC and B-EACC with space-time dual-resolved characteristics can be utilized for dynamic information encryption and optical logic gate applications. This study is the first to disclose the relation between the characteristics of molecular packing and the resultant URTP of 2D metal hybrid perovskites, significantly advancing the development of next-generation URTP materials for versatile applications.

Boosting Phosphorescence Efficiency of Microstructures by Forming a Triplet Exciplex System

AbstractLow‐dimensional crystal structures with long lifetime phosphorescence hold great potential in biological imaging, sensors, and micro/nanophotonics. However, the high‐efficient phosphorescence is still scarce on the micro/nanoscale due to the strong nonradiative transitions and quenching of long‐lifetime triplet state caused by the large specific surface area. Herein, a one doped microstructure with high quantum yield phosphorescence is reported by doping an electron‐acceptor (guest) into an electron‐donor (host). The formation of a triplet exciplex between the donor and acceptor enables the doped microcrystals to display highly efficient long‐lived emission with 63.1% quantum yield, while the phosphorescence emissions of microstructures from a neat donor and acceptor are negligible. The emission mechanism in relation to the exciplex is elaborated from temperature‐dependent luminescence behavior and theoretical calculation. This work provides an effective strategy for achieving efficient long‐lived emissions at the micro‐scale, which will accelerate the research and development of advanced miniaturized functional devices.

Dual-light emitting 3D encryption with printable fluorescent-phosphorescent metal-organic frameworks

Optical encryption technologies based on room-temperature light-emitting materials are of considerable interest. Herein, we present three-dimensional (3D) printable dual-light-emitting materials for high-performance optical pattern encryption. These are based on fluorescent perovskite nanocrystals (NCs) embedded in metal-organic frameworks (MOFs) designed for phosphorescent host-guest interactions. Notably, perovskite-containing MOFs emit a highly efficient blue phosphorescence, and perovskite NCs embedded in the MOFs emit characteristic green or red fluorescence under ultraviolet (UV) irradiation. Such dual-light-emitting MOFs with independent fluorescence and phosphorescence emissions are employed in pochoir pattern encryption, wherein actual information with transient phosphorescence is efficiently concealed behind fake information with fluorescence under UV exposure. Moreover, a 3D cubic skeleton is developed with the dual-light-emitting MOF powder dispersed in 3D-printable polymer filaments for 3D dual-pattern encryption. This article outlines a universal principle for developing MOF-based room-temperature multi-light-emitting materials and a strategy for multidimensional information encryption with enhanced capacity and security.

Synthesis of isophthalic acid-carbazole coordination polymers with stacking-dependent ultralong room temperature phosphorescence and white-light emission

Exploiting the relationship between the stacking modes of molecules and room-temperature phosphorescence (RTP) performance is of great important to design afterglow materials. A series of coordination polymers [Cd(CzIP)] (1) (H2CzIP = 5-(carbazol-9-yl) isophthalate), [Cd(CzIP)(DMI)] (2) (DMI = 1,3-Dimethyl-2-imidazolidinone) and [Cd2(CzIP)2(H2O)2] (3) base on carbazole–isophthalic acid are synthesized via a solvothermal method. These compounds exhibit stacking-dependent RTP. Compounds 1 and 2 exhibit obvious time-dependent RTP with the afterglow color from orange to green, and show white-light emission owing to fluorescence and phosphorescence dual emission. Compound 3, which features the strong π‒π stacking, showed the weakest phosphorescence with the shortest lifetime. It reveals that the phosphorescence efficiency is not proportional to the overlap of π-π stacking, the triplet excited states of discrete dimer mode rather than H-aggregation can dominate the generation of room-temperature phosphorescence. These results indicate that coordination induction is an efficient approach to regulate the aggregation of chromophores, further modulating the room-temperature phosphorescence.

Co-crystallization and Clustering Afforded Simultaneously Boosted Efficiency, Lifetime, and Color Tunability of Organic Afterglows.

Pure organic persistent room-temperature phosphorescence (p-RTP) is in urgent demand for advanced optoelectronic and bioelectronic applications. However, it remains an enormous challenge to modulate the emission colors while simultaneously boosting the phosphorescence lifetimes and efficiencies. Herein, we report the co-crystallization between melamine and cyclic imide-based non-conventional luminophores, which affords co-crystals owning multiple hydrogen bonds and effective clustering of electron-rich units, thus resulting in diverse emissive species with highly rigidified conformations and promoted spin-orbit coupling. Consequently, p-RTP co-crystals with simultaneously enhanced efficiencies and lifetimes of up to 12.0% and 898 ms, alongside remarkably improved color tunability, are obtained. These results may spur the future rational design of high-performance p-RTP materials and advance the mechanism of understanding of the origin of color-tunable phosphorescence.

Switching Singlet Exciton to Triplet for Efficient Pure Organic Room-Temperature Phosphorescence by Rational Molecular Design.

The design and regulation of phosphors are attractive but challenging because of the spin-forbidden intersystem crossing (ISC) process. Here, a new perspective on the enhancement of the ISC is proposed and demonstrated. Different from current strategies, the ISC yield (ΦISC) is enhanced by decreasing the fluorescence radiative transition rate constant (kF) via rational molecular designing rather than boosting the spin-orbit coupling by decorating the molecular skeleton with a heavy atom, heteroatom, or carbonyl. The kF of the designed molecule in this case is associated with the substituent position of the methoxy group, which alters the distribution of the front orbitals. The S0 → S1 transition of these compounds evolves from a bright state to a dark state gradually with the variation of the substituent position, accompanied by the decrease of kF and increase of ΦISC. The fluorescence emission is switched to phosphorescence emission successfully by regulating the kF. This work provides an alternative strategy to design efficient room-temperature phosphorescence material.

Loose Cocrystal Strategy for High‐Efficiency Near‐Infrared Phosphorescence

AbstractHarvesting triplet excitons of large π‐conjugate aromatic molecules via cocrystal engineering for attaining near‐infrared (NIR) phosphorescence has aroused wide attention due to its fundamental significance and practical application. Herein, the pyrene (Py)‐N, N’‐bis(1‐ethylpropyl)‐2,5,8,11‐tetrakis(p‐methyl‐phenyl)‐perylenediimide (MP) organic cocrystal is designed and fabricated via the solution self‐assembly method, which demonstrates the NIR phosphorescence with a maximum peak at 730 nm and a photoluminescence quantum yield of 34.2%. The singlet states with an intermediate energy level from MP molecules bridges singlet and triplet states of Py molecules, resulting in efficient NIR phosphorescence. Importantly, the loose packing pattern makes MP an excellent elementary molecule that can be assembled with a variety of aromatic molecules, from ternary to six‐membered benzene rings and even larger benzene skeletons. In contrast to the limitations of traditional cocrystal systems, cocrystal engineering based on MP molecules with weak π–π interactions is no longer limited to the careful selection and collocation of molecular structures, uncertain assembly behavior, and unpredictable properties. This work holds considerable insights for the exploration of novel NIR phosphorescent materials via a universal strategy.

Discrete Mononuclear Platinum(II) Complexes Realize High-Performance Red Phosphorescent OLEDs with EQEs of up to 31.8% and Superb Device Stability.

Designing mononuclear platinum(II) complexes that do not rely on intermolecular aggregation for high-performance red organic light-emitting diodes remains a formidable challenge. In this work, three robust red-emitting Pt(II) complexes w ere created by utilizing a rigid 4-coordination configuration, where the ligands w ere formed by linking electron-donor of triphenylamine (TPA) moieties with electron-acceptor of pyridine, isoquinoline, and/or δ-carboline units. The thermal stability, electrochemical, and photophysical properties of the complexes w ere thoroughly examined. The complexes display efficient red phosphorescence, with high photoluminescence quantum yields and short excited lifetimes. The OLEDs doped with these complexes exhibit high maximum external quantum efficiencies (EQEs) of up to 31.8% with minimal efficiency roll-off even at high brightness. Significantly, the devices demonstrated exceptional long operational lifetime, with a T90 lifetime of over 14000 hours at initial luminance of 1000cd m-2 , indicating the potential for these complexes to be practically utilized. This article is protected by copyright. All rights reserved.