Phosphorescence Emission Research Articles

Ligand Design and Preparation, Photophysical Properties, and Device Performance of an Encapsulated-Type Pseudo-Tris(heteroleptic) Iridium(III) Emitter.

The organic molecule 2-(1-phenyl-1-(pyridin-2-yl)ethyl)-6-(3-(1-phenyl-1-(pyridin-2-yl)ethyl)phenyl)pyridine (H3L) has been designed, prepared, and employed to synthesize the encapsulated-type pseudo-tris(heteroleptic) iridium(III) derivative Ir(κ6-fac-C,C',C″-fac-N,N',N″-L). Its formation takes place as a result of the coordination of the heterocycles to the iridium center and the ortho-CH bond activation of the phenyl groups. Dimer [Ir(μ-Cl)(η4-COD)]2 is suitable for the preparation of this compound of class [Ir(9h)] (9h = 9-electron donor hexadentate ligand), but Ir(acac)3 is a more appropriate starting material. Reactions were carried out in 1-phenylethanol. In contrast to the latter, 2-ethoxyethanol promotes the metal carbonylation, inhibiting the full coordination of H3L. Complex Ir(κ6-fac-C,C',C″-fac-N,N',N″-L) is a phosphorescent emitter upon photoexcitation, which has been employed to fabricate four yellow emitting devices with 1931 CIE (x:y) ∼ (0.52:0.48) and a maximum wavelength at 576 nm. These devices display luminous efficacies, external quantum efficiencies, and power efficacies at 600 cd m-2, which lie in the ranges 21.4-31.3 cd A-1, 7.8-11.3%, and 10.2-14.1 lm W1-, respectively, depending on the device configuration.

Shallow Traps in Carbon Nitride Quantum Dots to Achieve 6.47 s Ultralong Lifetime and Wavelength‐Tunable Room Temperature Phosphorescence

AbstractRoom temperature phosphorescent (RTP) carbon dots (CDs) have the defects of short lifetime, single wavelength, and poor stability. Most approaches to achieve RTP CDs are based on stabilizing excited triplet state excitons and suppressing nonradiative transitions by providing a rigid environment. The internal structure of CDs has not been followed to address the issue of triplet state exciton quenching. Herein, boron (B) is doped into the framework of carbon nitride quantum dots (CNQDs) to create BN bonds and generate trap state, thus reducing the degree of conjugation and constructing defects. The excited triplet excitons are captured by the defects and stored in the traps from which they escape under thermal activation—this in turn gives rise to an ultralong lifetime RTP. Based on the abovementioned considerations, 6.47 s ultralong‐lifetime deep blue RTP CNQDs with phosphorescent emission wavelength at 418 nm are achieved. This is a significantly longer lifetime than for most deep‐blue RTP CDs. By increasing the conjugation of the precursor, another 1.55 s of green RTP CNQDs at 530 nm is obtained. The difference in lifetime and wavelength between the two phosphorescent CNQDs as well as their excellent stability leads to potential applications in anti‐counterfeiting and information encryption.

Modulating Narrow-Band Phosphorescence of Pt2Au4 Cluster Complexes by Differently Positioned Bis(acetylide)-Naphthalene Linkers

To modulate phosphorescent characteristics of Pt2Au4 complexes with differently positioned bis(acetylide)naphthalene as a bridging ligand, four isomeric Pt2Au4 complexes (1–4) linked by 1,4-bis(acetylide)naphthalene (1), 1,5-bis(acetylide)naphthalene (2), 2,6-bis(acetylide)naphthalene (3), and 2,7-bis(acetylide)naphthalene (4) are elaborately designed and prepared. The Pt2Au4 complexes are strongly phosphorescent with the quantum yields as high as 52% in CH2Cl2 solutions, in strikingly contrast to weak phosphorescence of bis(acetylide)naphthalene-linked Pt2 precursors. After the formation of Pt2Au4 cluster structures, the increased molecular rigidity dramatically suppresses nonradiative relaxation, which becomes less competitive in contrast to the radiative relaxation of the emitting state, thus resulting in a remarkable enhancement of the quantum yields. Depending on the positions of bis(acetylide) groups attached to naphthalene rings, the phosphorescence of Pt2Au4 isomers in CH2Cl2 solutions follows 1 (640 nm) → 2 (582 nm) → 3 (567 nm) → 4 (529 nm) to show progressive blue shifts. As demonstrated by photophysical and theoretical studies, vibronic-structured narrow-band emission with a full width at half maxima (fwhm) of 707–1073 cm–1 is primarily ascribable to ligand-centered triplet states localized at bis(acetylide)naphthalenes, which is dramatically activated upon the formation of the Pt2Au4 cluster because the energy harvested by two PtAu2 cluster moieties is effectively transferred to bridging bis(acetylide)naphthalene. Taking advantage of Pt2Au4 complexes 1–4 as phosphorescent emitters, solution-processed OLEDs achieve narrow-band electroluminescence with peak external quantum efficiency of 11.0% for red-emitting complex 1 (fwhm = 45 nm or 1058 cm–1), 9.4% for orange-emitting complex 2 (fwhm = 33 nm or 960 cm–1), 13.7% for yellow-emitting complex 3 (fwhm = 33 nm or 1029 cm–1), and 15.2% for green-emitting complex 4 (fwhm = 24 nm or 848 cm–1).

Polymerization-Induced Crystallization of Dopant Molecules: An Efficient Strategy for Room-Temperature Phosphorescence of Hydrogels

Conventional hydrogels such as polyacrylamide and polyacrylic acid ones seldom exhibit phosphorescences at ambient conditions, which limit their applications as optical materials. We propose and demonstrate here a facile strategy to afford these hydrogels with room-temperature phosphorescence by polymerization-induced crystallization of dopant molecules that results in segregation and confinement of the gel matrix with carbonyl groups and thus clusterization-induced phosphorescence. As a model system, crown ethers (CEs) are dissolved in an aqueous solution of concentrated acrylamide that greatly increases the solubility of CEs. During the polymerization process, CEs crystallize to form large spherulites in the polyacrylamide hydrogel. The crystallization arises from the drastically reduced solubility of CEs after the conversion of monomers to polymers during the gel synthesis. The resultant composite hydrogel with a water content of 67 wt % exhibits extraordinary phosphorescence behavior yet maintains good stretchability and resilience. We found that the partial gel matrix is squeezed and confined by in situ-formed crystals, leading to carbonyl clusters and thus phosphorescence emission. The composite gel shows green phosphorescence with an emission peak at 512 nm and a lifetime of 342 ms. The afterglow emission is detectable by the naked eye for several seconds. This strategy has good universality, as validated in other hydrogels with different polymeric matrices and dopant molecules. The development of hydrogels with good mechanical and phosphorescent properties should merit the design of multifunctional soft machines with applications in biomedical and engineering fields.

Efficient, Color-Stable, and Long-Lived White Organic Light-Emitting Diodes Utilizing Phosphorescent Molecular Aggregates.

Highly efficient and stable single-stack hybrid white organic light-emitting diode (WOLED) devices are developed using two emissive layers: one with amber-colored phosphorescent molecular-aggregate emission from the Pd(II) complex, Pd(II) 7-(3-(pyridine-2-yl-κN)phenoxy-κC)(benzo-κC)([c]benzo[4,5]imidazo-κN)[1,2-a][1,5]naphthyridine, Pd3O8-Py5, and the other with blue fluorescence emission. An optimized device structure achieves high color stability under various current densities, an external quantum efficiency (EQE) of 45.5%, a power efficiency of 97.4 Lm W-1 , and an estimated LT95 (operational time to 95% of the initial luminance) of 50 744 h at an initial luminance of 1000cd m-2 .

Effect of aggregation on thermally activated delayed fluorescence and ultralong organic phosphorescence: QM/MM study

Aggregation-induced thermally activated delayed fluorescence (TADF) phenomena have attracted extensive attention recently. In this paper, several theoretical models including monomer, dimer, and complex are used for the explanation of the luminescent properties of (R)-5-(9H-carbazol-9-yl)-2-(1,2,3,4-tetrahydronaphthalen-1-yl)isoindoline-1,3-dione ((R)-ImNCz), which was recently reported [Chemical Engineering Journal 418 129167 (2021)]. The polarizable continuum model (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method are adopted in simulation of the property of the molecule in the gas phase, solvated in acetonitrile and in aggregation states. It is found that large spin–orbit coupling (SOC) constants and a smaller energy gap between the first singlet excited state and the first triplet excited state (ΔE st) in prism-like single crystals (SCp-form) are responsible for the TADF of (R)-lmNCz, while no TADF is found in block-like single crystals (SCb-form) with a larger ΔE st. The multiple ultralong phosphorescence (UOP) peaks in the spectrum are of complex origins, and they are related not only to ImNCz but also to a minor amount of impurities (ImNBd) in the crystal prepared in the laboratory. The dimer has similar phosphorescence emission wavelengths to the (R)-lmNCz-SCp monomers. The complex composed of (R)-lmNCz and (R)-lmNBd contributes to the phosphorescent emission peak at about 600 nm, and the phosphorescent emission peak at about 650 nm is generated by (R)-lmNBd. This indicates that the impurity could also contribute to emission in molecular crystals. The present calculations clarify the relationship between the molecular aggregation and the light-emitting properties of the TADF emitters and will therefore be helpful for the design of potentially more useful TADF emitters.

A Novel Photoluminescent Ag/Cu Cluster Exhibits a Chromic Photoluminescence Response towards Volatile Organic Vapors.

A new Ag/Cu bimetallic cluster [Ag10Cu6(bdppthi)2(C≡CPh)12(EtOH)2](ClO4)4 (1, bdppthi = N,N'-bis(diphenylphosphanylmethyl)-tetrahydroimidazole) exhibited strong phosphorescent (PL) emission at 644 nm upon excitation at 400 nm. Removal of the coordinated EtOH molecules in 1 resulted in derivative 1a, which exhibited significant red-shifted emission at 678 nm. The structure and PL of 1 was restored on exposure to EtOH vapor. Cluster 1a also exhibited a vapor-chromic PL response towards other common organic solvent vapors including acetone, MeOH and MeCN. A PMMA film of 1a was developed as a reusable visible sensor for MeCN.

Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission.

The experimental measurement of the photophysical and chiroptical properties of helicene-based π-conjugated emitters with electron-accepting (-CN, -py, -NO2) or donating (TMS, NMe2, NH2) moieties is reported at low temperature (77 K). The samples exhibit strong circularly polarized phosphorescence in frozen solution of 2-MeTHF, with a luminescence dissymmetry factor reaching 1.6 × 10-2 and a lifetime of over 0.46 s for the most active molecule, the nitro compound. The theoretical investigation shows that although the singlet (S1) and triplet (T1) excited-state emissions mainly arise from the helicene core, the rotatory strengths of the spin-allowed versus spin-forbidden emission have opposite signs. Further analysis of the spin-orbit coupling matrix elements shows that there is no strong mixing between S1 and T1, justifying the different signs of the rotatory strengths. In the case of the nitro compound, the enhanced phosphorescence emission is due to an efficient intersystem crossing.

Dual-Emission 2D Blue Luminescent Organic Silver Chalcogenide for Highly Selective Pb2+ Detection in an Aqueous Medium

Crystalline organic metal chalcogenides (OMCs) are a class of organic-inorganic hybrid semiconducting materials with continuous M-X (X = S, Se, Te) networks formed by the combination of metal nodes and chalcogen atoms from the organic ligands, which display great potentials in the fields of optoelectronics, catalysis, sensing, as well as energy conversion and storage. Here, we synthesized a wave-like 2D OMC material, [(AgBF4)2Me6BHS]n (Ag-BHSMe), from AgBF4 and 1,2,3,4,5,6-hexa(methylselanyl)benzene (Me6BHS) through a simple homogeneous reaction. In the solid state, Ag-BHSMe exhibits both fluorescence emission at room temperature and phosphorescent emission at 77 K. TEM, SEM, and confocal microscopy revealed that it is an intrinsic blue luminescent microcrystalline material. In addition, we found that it exhibited a highly selective fluorescence enhancement response to Pb2+ in an aqueous solution in the range of 10-4 to 10-2 mol L-1, which demonstrates its potential as a turn-on probe for the detection of lead ions.

Long afterglow particle enables spectral and temporal light management to boost photosynthetic efficiency

Herein, we develop a strategy of matched spectral and temporal light management to improve photosynthetic efficiency by co-assembling natural thylakoid membrane (TM) with artificial long afterglow particle (LAP). To be specific, LAP with excellent stability and biocompatibility possesses the capabilities of light conversion and storage, optically-matched with the absorption of TM. These favorable features permit LAP as an additional well-functioned light source of photosynthesis performed by TM. As a consequence, enhanced photosynthesis is achieved after co-assembly, compared with pure TM. Under light, the rates of electron transfer, oxygen yield and adenosine triphosphate (ATP) production in this biohybrid architecture are boosted owing to down-conversion fluorescence emission from LAP. Under dark, persistent phosphorescence emission in charged LAP facilitates continual photosynthesis of TM, while that of pure TM almost stops immediately. This proof-of-concept work opens a new route to augment the photosynthetic efficiency of green plants by utilizing precise light-managed materials.

F, N co-doped carbon nanomaterials for multi-level information encryption: Room-temperature phosphorescence and solid-state fluorescence

The non-radiative transition of triplet excitons limits the emission of room-temperature phosphorescence (RTP). In this paper, F, N co-doped carbon nanomaterials including carbon dot solutions (L-CDs) with cyan fluorescence and solid-state carbon nanowires (S-CNWs) with yellow fluorescence were successfully prepared by the one-pot hydrothermal method. Interestingly, L-CDs@PVA composites with green RTP were obtained by mixing L-CDs with PVA. The RTP production was attributed to F, N related heteroatomic functional groups on the surface of L-CDs. The C-N, CN bonds form lone electron pairs, which promote the electron transition from n→π∗. The F doping reduces the energy gap from the single to the triplet state, which facilitates the inter-system crossing (ISC) process and increases the radiative transition of the triplet exciton to produce RTP. In addition, PVA forms abundant hydrogen bonds with L-CDs to effectively immobilize the luminescence center and isolate atmospheric oxygen, so that L-CDs@PVA has stable phosphorescence emission at room temperature and this phosphorescence is reversible in dry and wet states. In contrast, S-CNWs displayed solid-state yellow fluorescence, but no phosphorescence even though doped into the PVA matrix (S-CNWs@PVA). Therefore, based on the different characteristics of fluorescence and phosphorescence of L-CDs and S-CNWs, a complex, multi-level information encryption method is proposed and the potential applications of S-CNWs powder for fingerprint recording are explored.

Photoreaction Boosting Phosphorescence Cascade Energy Transfer Based on Cucurbit[8]Uril Biaxial Polypseudorotaxane

AbstractCascade energy capturers based on supramolecular assembly have recently generated great research interest in the field of luminescent materials. Herein is reported a cucurbit[8]uril (CB[8])‐encapsulated coumarin‐bridged phenylpyridinium salt (G) to form biaxial polypseudorotaxane (G⊂CB[8]), which not only induces the phosphorescence of the guest G, but also activates the photodimerization of coumarin functional group in the CB[8] cavity (G‐dimer⊂CB[8]) to further boost its phosphorescence emission, extending the phosphorescence lifetime from 271.3 to 430.3 µs and the quantum yield from 5.1% to 25.7% in aqueous solution. After co‐assembly with amphiphilic calixarene (SC4AD), the supramolecular biaxial polypseudorotaxane G‐dimer⊂CB[8] is changed to the nanoparticle. Compared with the alone G‐dimer⊂CB[8], the phosphorescence intensity of G‐dimer⊂CB[8]@SC4AD is significantly enhanced with the phosphorescence lifetime extending to 2.11 ms. Subsequently, by doping commercial dye rhodamine B (RhB) in the G‐dimer⊂CB[8]@SC4AD assembly, an ultrahighly efficient phosphorescence‐harvesting energy transfer process occurs with an energy transfer efficiency (ΦET) of 72.3% and an antenna effect of 396.8. Furthermore, the cascaded room temperature phosphorescence harvesting system is constructed via introducing the secondary near‐infrared (NIR) acceptors Nile blue or Cy5 in the G‐dimer⊂CB[8]@SC4AD:RhB system, which possesses a good biocompatibility and is successfully applied to NIR delayed fluorescence targeted imaging in HeLa cell.

Insight into the Heavy Atom Effect Induced by Environmental Heavy Atoms for Gadolinium-Labeled Hematoporphyrin Monomethyl Ether

Environmental heavy atoms can further enhance the room temperature phosphorescence (RTP) emissions of gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME) by way of the external heavy atom effect (HAE). However, the macroscopic phosphorescence intensity covered the intrinsic effect of the environmental heavy atoms. In this study, a method of separating the external HAE from the total is performed, and a quantity to describe the intrinsic nature of external HAE is defined. The environmental Gd3+ concentration evolution of the phosphorescent transition rate (kP) is obtained by correlated absorption, emission, and time-resolved spectroscopy. The kP increases linearly with environmental Gd3+ concentration, while the intercept kP0 coincides with that of the internal HAE. The slope κ could be calculated, and it is a quantity free of the Gd3+ concentration and only relies on the type of environmental heavy atoms. In addition, the environmental Lu3+ exhibits similar functionality to Gd3+ in external HAE. Environmental Pd2+ quenches the phosphorescence intensity macroscopically, while it enhances the HAE intrinsically. Our method provides an alternative insight into the intrinsic nature of environmental heavy atoms.

Synthesis, Photophysics and Tunable Reverse Saturable Absorption of Bis-Tridentate Iridium(III) Complexes via Modification on Diimine Ligand.

Five novel bis-tridentate Ir(III) complexes (Ir-1−Ir-5) incorporating versatile N^N^C ligands and a N^C^N ligand (1,3-di(2-pyridyl)-4,6-dimethylbenzene) were synthesized. With the combination of experimental and theoretical methods, their steady and transient state characteristics were researched scientifically. The UV-visible absorption spectra show that the broadband charge transfer absorbance of those bis-tridentate Ir(III) complexes can reach 550 nm, all of these complexes reveal the long-lasting phosphorescent emission. Because the excited-state absorption is more powerful than the ground-state absorption, a sturdy reverse saturable absorption (RSA) process can ensue in the visible and near-infrared regions when the complexes are exposed to a 532 nm laser. Therefore, the optical power limiting (OPL) effect follows the trend: Ir-5 > Ir-4 ≈ Ir-3 > Ir-2 > Ir-1. Generally speaking, the expansion of π-conjugation and the introduction of electron donating/withdrawing groups on the N^N^C ligand could effectively elevate the OPL effect. Therefore, these octahedral bis-tridentate Ir(III) complexes might be exploited as potential OPL materials.

Conformationally confined three-armed supramolecular folding for boosting near-infrared biological imaging.

Herein, a triphenylamine derivative (TP-3PY) possessing 4-(4-bromophenyl)pyridine (PY) as an electron-accepting group and tris[p-(4-pyridylvinyl)phenyl]amine (TPA) with large two-photon absorption cross-sections as an electron-donating group was obtained, and showed intense absorption in the visible light region (λmax = 509 nm) and weak near-infrared (NIR) fluorescence emission at 750 nm. After complexation with cucurbit[8]uril (CB[8]), TP-3PY showed bright NIR fluorescence emission at 727 nm and phosphorescence emission at 800 nm. When the supramolecular assembly (TP-3PY⊂CB[8]) further interacted with dodecyl-modified sulfonatocalix[4]arene (SC4AD), the fluorescence and phosphorescence emissions were further enhanced at 710 and 734 nm, respectively. However, only the fluorescence emission of TP-3PY was enhanced in the presence of cucurbit[7]uril (CB[7]) and SC4AD. More interestingly, the photoluminescence of TP-3PY⊂CB[8]@SC4AD and TP-3PY⊂CB[7]@SC4AD assemblies could be excited by both visible (510 nm) and NIR light (930 nm). Finally, these ternary supramolecular assemblies with bright NIR light emission were applied to lysosome imaging of tumor cells and real-time biological imaging of mice.

Regulation of various photo-active UOPs in a polymer matrix by tuning intermolecular charge transfer

Phosphorescent emitters, CzBN and CzPN, show intense UOP in PVA and PMMA matrices. The UOP performance in PVA matrices does not require a photo-active process, while different durations of photo-active process are required in PMMA.

Revisiting organic charge-transfer cocrystals for wide-range tunable, ambient phosphorescence.

Simple and efficient designs that enable a wide range of phosphorescence emission in organic materials have ignited scientific interest across diverse fields. One particularly promising approach is the cocrystallization strategy, where organic cocrystals are ingeniously formed through relatively weaker and dynamic non-covalent interactions. In our present study, we push the boundaries further by extending this cocrystal strategy to incorporate donor-acceptor components, stabilized by various halogen bonding interactions. This non-covalent complexation triggers ambient, charge-transfer phosphorescence (3CT), which can be precisely tuned across a broad spectrum by a modular selection of components with distinct electronic characteristics. At the core of our investigation lies the electron-deficient phosphor, pyromellitic diimide, which, upon complexation with different donors based on their electron-donating strength, manifests a striking array of phosphorescence emission from CT triplet states, spanning from green to yellow to reddish orange accompanied by noteworthy quantum yields. Through a systematic exploration of the electronic properties using spectroscopic studies and molecular organization through single-crystal X-ray diffraction, we decisively establish the molecular origin of the observed phosphorescence. Notably, our work presents, for the first time, an elegant demonstration of tunable 3CT phosphorescence emission in intermolecular donor-acceptor systems, highlighting their immense significance in the quest for efficient organic phosphors.

Mesomerism induced temperature-dependent multicomponent phosphorescence emissions in ClBDBT.

Quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics (MD) methods were applied to systematically investigate the temperature-dependent phosphorescence emission of dibenzo[b,d]thiophen-2-yl(4-chlorophenyl)methanone (ClBDBT) and its derivatives. The calculated temperature-dependent spectra on the lowest triplet state (T1) are in good agreement with the experimental observations, which means that the two-component white light emission should stem from the T1 state. The further MD simulations demonstrate the existence of two mesomerism structures at room temperature which can emit two lights simultaneously. The multi-component light emissions induced by mesomerism structures have advantages in balancing the distribution of excitons which could be beneficial to obtain pure white light along with stable Commission Internationale de l'Éclairage (CIE) coordinates. We hope this mesomerism concept can be further used to design new white light emitters based on room-temperature phosphorescence.

Evolution and fabrication of carbon dot-based room temperature phosphorescence materials.

Traditional room temperature phosphorescence (RTP) materials usually include organometallic composites and pure organic compounds, which generally possess the disadvantages of high toxicity, high cost and complicated preparation. Carbon dots (CDs) are a new kind of luminescent material and have attracted widespread attention due to their benefits of excellent tunable emission, nice biocompatibility, cost-effectiveness, facile preparation and environmental friendliness. Since photoluminescence is an important luminescent property of carbon-based fluorescent nanomaterials, CD-based RTP materials have sparked a new research wave due to the properties of extremely long phosphorescence lifetime, large Stokes shift and high environmental sensitivity. In order to construct excellent CD-based RTP materials, many attempts have been made, and the corresponding progress has been achieved. Herein, we summarize the progress in CD-based RTP materials in recent years, mainly focusing on the outstanding contributions over the years, phosphorescence emission, phosphorescence lifetime, preparation and application of CD-based RTP materials. In particular, this review provides a comprehensive summary and analyze the outstanding contributions in the fields of the phosphorescence emission and phosphorescence lifetime of CD-based RTP materials over the years. Finally, several existing challenges and the future outlook of RTP materials based on CDs have been put forward.

Phosphorescence emission from spatial stacks of phenanthrene units in oligo(9,10-phenanthrene)s.

The covalent linkage of phenanthrene units at 9 and 10 positions resulted in a broadening of the absorption band and a red-shift of the fluorescence band in ethanol compared with its monomer. Spatial stacking of phenanthrene units also altered the spectral shape of phosphorescence emission, and the oligomer film emitted phosphorescence at room temperature.