Red Phosphorescence Research Articles

Enabling controllable time‐dependent phosphorescence in carbonized polymer dots based on chromophore excited triplet energy level modulation by ionic bonding

Time‐dependent phosphorescence color (TDPC) materials are highly attractive for realizing multitiered dynamic information encryption and anti‐counterfeiting. It’s extremely challenging to modulate puzzle of multiple luminescence species and understand the intrinsic mechanism. Herein, we demonstrate a novel and synthesize‐friendly strategy to develop a high contrast TDPC carbonized polymer dots (CPDs) with adjustable lifetime and quantum yields. The ionic bonding is introduced in self‐protected CPDs to effectively tune the excited triplet energy level of chromophores, and promote the stable existence of L‐aspartic (AA) with green phosphorescence at 545 nm, and alkali metal aspartates (AA‐M) with red phosphorescence at 665 nm. The precise regulation for TDPC lifetime can be achieved based on heavy atom effort and crosslink‐enhanced emission (CEE) effect. And, the efficient radiative energy transfer could be proven as an intrinsic mechanism for better understanding the TDPC materials. These results further expand on the fundamental principle to design high‐quality TDPC materials with more flexible regulation for luminescence properties, providing a major step forward in broadening the scope of smart phosphorescence applications.

Enabling controllable time‐dependent phosphorescence in carbonized polymer dots based on chromophore excited triplet energy level modulation by ionic bonding

Time‐dependent phosphorescence color (TDPC) materials are highly attractive for realizing multitiered dynamic information encryption and anti‐counterfeiting. It’s extremely challenging to modulate puzzle of multiple luminescence species and understand the intrinsic mechanism. Herein, we demonstrate a novel and synthesize‐friendly strategy to develop a high contrast TDPC carbonized polymer dots (CPDs) with adjustable lifetime and quantum yields. The ionic bonding is introduced in self‐protected CPDs to effectively tune the excited triplet energy level of chromophores, and promote the stable existence of L‐aspartic (AA) with green phosphorescence at 545 nm, and alkali metal aspartates (AA‐M) with red phosphorescence at 665 nm. The precise regulation for TDPC lifetime can be achieved based on heavy atom effort and crosslink‐enhanced emission (CEE) effect. And, the efficient radiative energy transfer could be proven as an intrinsic mechanism for better understanding the TDPC materials. These results further expand on the fundamental principle to design high‐quality TDPC materials with more flexible regulation for luminescence properties, providing a major step forward in broadening the scope of smart phosphorescence applications.

Ag:MoO3:Yb semi-transparent electrode for top emission organic light-emitting didoes

Silver (Ag) is widely used as a cathode in top-emission organic light-emitting diodes (TEOLEDs) for its high reflectivity and conductivity. However, its high absorption, thickness-dependent transmittance, and high work function require further improvement. While Ag:MoO3 alloy has emerged as an alternative, it still needs further enhancement. In this study, we developed a ternary Ag:MoO3:Yb semi-transparent electrode, improving both the optical and electrical properties of the existing binary system. For example, The 30 nm-thick Ag:MoO3:Yb 4:3:3 film exhibited average transmittance, reflectance, and absorption of 64%, 12%, and 24%, respectively. Additionally, the Ag:MoO3:Yb showed a uniform transmittance spectrum in the visible wavelength range. The photoelectron spectroscopy results showed Ag:MoO3:Yb 4:3:3 film has a low work function of 3.69eV. Despite relatively high sheet resistance around 82~130 Ω/sq, the red phosphorescence TEOLEDs incorporating Ag:MoO3:Yb as cathode showed improved device performances compared to the control device with Ag:MoO3 30% where the current efficiency increased by up to 1.7 times and the power efficiency by up to 2.6 times. Furthermore, the optimized Ag:MoO3:Yb devices with good charge balance resulted in a relatively longer lifetime up to 80% of initial luminance (LT80) of 166hr, which are higher performance than those of the device with Ag:MoO3 30%.

Delayed luminescence and thermoluminescence in laboratory-grown diamonds

The “blue-green” phosphorescence/thermoluminescence is most commonly observed in diamonds following excitation at or above the indirect band gap and has been explained by a substitutional nitrogen-boron donor-acceptor pair recombination model. “Orange” and “red” phosphorescence have also been frequently observed in laboratory-grown near-colorless high-pressure high-temperature diamonds following optical excitation and their luminescence mechanisms are shown to be different from that of the blue-green phosphorescence. The physics of the orange and red luminescence and phosphorescence bands including the optical-excitation dependency (UV-NIR), temperature dependency (20K–573K), and related charge transfer process are investigated by a combination of self-built time-resolved imaging/spectroscopic techniques. In this paper, an alternative model for long-lived phosphorescence based on charge trapping is proposed to explain the orange phosphorescence/thermoluminescence band. Additionally, the red phosphorescence band is attributed to point defect, which possibly has a three-level phosphorescence system. Published by the American Physical Society 2024

Confinement Microenvironment Regulation of Carbon Dots in Zeolite for Multi‐Mode Time‐Dependent Phosphorescence Color Evolution

Matrix immobilization has been proven to be a favored method for enhancing the phosphorescence of carbon dots (CDs), however, it remains a significant challenge to realize time‐dependent phosphorescence colors (TDPC) by embedding CDs with single emission center. In this study, we present a novel matrix‐controlling strategy to regulate the microenvironment of CDs by doping limited Mn2+ in zeolite. The surrounding environment influences the surface state of the CDs, leading to the formation of different excitons. At low temperatures, Mn‐coordinated CDs (C‐CDs) show fast‐decaying green phosphorescence, while non‐coordinated CDs (NC‐CDs) exhibit inherent slow‐decaying blue phosphorescence. Notably, the energy transfer occurs between NC‐CDs and Mn2+ to produce an ultrafast‐decaying red phosphorescence, with the intensity of the red component increasing as the temperature rises. The interplay of these luminescent centers with distinct decay rates activates fascinating multi‐mode TDPC behavior as the temperature changes, resulting in dynamic afterglow evolutions from red to green at 298 K, orange to green at 273 K, and green to cyan to blue at 77 K. Leveraging the diverse luminescence of CDs@MnAPO‐5, a multi‐dimensional dynamic afterglow color pattern was developed for advanced anti‐counterfeiting applications.

Confinement Microenvironment Regulation of Carbon Dots in Zeolite for Multi-Mode Time-Dependent Phosphorescence Color Evolution.

Matrix immobilization has been proven to be a favored method for enhancing the phosphorescence of carbon dots (CDs), however, it remains a significant challenge to realize time-dependent phosphorescence colors (TDPC) by embedding CDs with single emission center. In this study, we present a novel matrix-controlling strategy to regulate the microenvironment of CDs by doping limited Mn2+ in zeolite. The surrounding environment influences the surface state of the CDs, leading to the formation of different excitons. At low temperatures, Mn-coordinated CDs (C-CDs) show fast-decaying green phosphorescence, while non-coordinated CDs (NC-CDs) exhibit inherent slow-decaying blue phosphorescence. Notably, the energy transfer occurs between NC-CDs and Mn2+ to produce an ultrafast-decaying red phosphorescence, with the intensity of the red component increasing as the temperature rises. The interplay of these luminescent centers with distinct decay rates activates fascinating multi-mode TDPC behavior as the temperature changes, resulting in dynamic afterglow evolutions from red to green at 298 K, orange to green at 273 K, and green to cyan to blue at 77 K. Leveraging the diverse luminescence of CDs@MnAPO-5, a multi-dimensional dynamic afterglow color pattern was developed for advanced anti-counterfeiting applications.

A Pair of Deep Red Phosphorescent Responsive Emissive Cyclometalated Iridium (III) Complexes as Carbonic Anhydrase Inhibitor and Effective Theranostic Photosensitizer

ABSTRACTHerein, two deep red phosphorescent responsive emissive cyclometalated iridium (III) complexes with CAIX inhibition moiety was designed and synthesized; they can penetrate into living cells quickly and mainly located in the lysosome. They showed a strong binding affinity towards CAIX in vitro and effectively reduced cellular expression of CAIX. Moreover, the tethered CAIX‐inhibition moiety of benzene sulfonamide can decrease the inherent cytotoxicity of Ir(III) complex towards normal cells and improve killing selectivity towards cancer cells in dark; Ir3 and Ir4 exhibit approximately five to eight times higher killing selectivity than that of cisplatin; they exhibit satisfied photodynamic therapy effect under irradiation of 425 nm, ultimately resulting in apoptosis of cancer cell, which is accompanied with weakening of extracellular acidification, increased inhibition of cellular CAIX expression, significant loss of mitochondrial membrane potential, and elevated level of reactive oxygen. Herein, our work may demonstrate that combination of inhibition CAIX and metal photosensitizer may provide a promising strategy for constructing a novel theranostic platform.

Cocrystallization‐Induced Red Ultralong Organic Phosphorescence

AbstractOrganic cocrystals formed through multicomponent self‐assembly have attracted significant interest owing to their clear structure and tunable optical properties. However, most cocrystal systems suffer from inefficient long‐wavelength emission and low phosphorescence efficiency due to strong non‐radiative processes governed by the energy gap law. Herein, an efficient long‐lived red afterglow is achieved using a pyrene (Py) cocrystal system incorporating a second component (NPYC4) with thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) properties. The cocrystal (NPYC4‐Py) not only inherits the excellent luminescence of its monomeric counterparts, but also exhibits unique dual‐mode characteristics, including persistent TADF and UOP emission with a high quantum yield of 58 % and a lifetime of 362 ms. The precise cocrystal stacking distinctly reveals that intermolecular interactions lock the cocrystal formation and weaken the intermolecular π‐π interactions between NPYC4 and Py, thereby stabilizing the excited triplet excitons. Furthermore, the favorable energy level of NPYC4 acts as a bridge, reducing the energy gap between the S1 and T1 states for Py, therefore activating its red phosphorescence from Py. This research provides direct insights into achieving efficient red UOP through co‐crystallization.

Cocrystallization-Induced Red Ultralong Organic Phosphorescence.

Organic cocrystals formed through multicomponent self-assembly have attracted significant interest owing to their clear structure and tunable optical properties. However, most cocrystal systems suffer from inefficient long-wavelength emission and low phosphorescence efficiency due to strong non-radiative processes governed by the energy gap law. Herein, an efficient long-lived red afterglow is achieved using a pyrene (Py) cocrystal system incorporating a second component (NPYC4) with thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) properties. The cocrystal (NPYC4-Py) not only inherits the excellent luminescence of its monomeric counterparts, but also exhibits unique dual-mode characteristics, including persistent TADF and UOP emission with a high quantum yield of 58 % and a lifetime of 362 ms. The precise cocrystal stacking distinctly reveals that intermolecular interactions lock the cocrystal formation and weaken the intermolecular π-π interactions between NPYC4 and Py, thereby stabilizing the excited triplet excitons. Furthermore, the favorable energy level of NPYC4 acts as a bridge, reducing the energy gap between the S1 and T1 states for Py, therefore activating its red phosphorescence from Py. This research provides direct insights into achieving efficient red UOP through co-crystallization.

Conformation‐Controlled Double Phosphorescence Components From A Single Organic Molecule: Time‐Dependent and Excitation‐Dependent Wide‐Range Afterglow Color Change

AbstractDouble phosphorescence components from a single organic molecule is rarely reported before because most organic molecules must follow Kasha's rule and merely emit phosphorescence from T1 state. We discover a unique phenomenon of conformation‐controlled expression of double phosphorescence components. The green phosphorescence component and the red phosphorescence component are assigned to the dinaphthylamine moiety and the pyrene unit of N,N‐di(naphthalen‐2‐yl)pyren‐1‐amine (NaPy), respectively. NaPy shows time‐dependent and excitation‐dependent afterglow color change in copolymerized MMA film at room temperature due to simultaneous expression of the double phosphorescence components. However, in PMMA film and copolymerized MA film, NaPy just expresses the red phosphorescence component, suggesting that matrix rigidity greatly affects expression of the double phosphorescence components via altering conformation of NaPy. In low‐rigidity matrix, the NaPy conformation is dyanmic due to free rotation and triplet excitons relax to T1 state via inner conversion or vibration relaxation, leading to the sole expression of the red phosphorescence component. In high‐rigidity matrix, the highly twisted conformation of NaPy is stabilized due to limitation of rotation and triplet excitons at T1 state and T2 state return to S0 state separately, resulting in simultaneous expression of the double phosphorescence components. Thus, NaPy follows Kasha's rule in low‐rigidity matrix but disobeys Kasha's rule in high‐rigidity matrix. In high‐rigidity matrix, the dinaphthylamine moiety and the pyrene unit can function relatively independently, resulting in time‐dependent and excitation‐dependent wide‐range afterglow color change.

Stimulating Chiral Selective Expression of Room Temperature Phosphorescence for Chirality Recognition.

Chiral recognition is crucial for applications in chiral purity assessment and biomedical fields. However, achieving chiral recognition through visible roomtemperature phosphorescence remains challenging. Here, two chiral molecules, designated as host and guest are synthesized, which possess similar structural configurations. A viable strategy involving a chiral configuration-dependent energy transfer process to enable selective phosphorescence expression is proposed, thereby enabling chiral recognition in a host-guest doping system. The chiral and structural similarity between host and guest facilitates efficient Dexter energy transfer due to the reduced spatial distance between the molecules. This mechanism significantly enhances the intensity of red phosphorescence from the guest molecule, characterized by an emission peak at 612nm and a prolonged lifetime of 32.7ms. This work elucidates the mechanism of chiral-dependent energy transfer, demonstrating its potential for selectively expressing phosphorescence in chiral recognition.

Ancillary Ligand Steric Effects and Cyclometalating Ligand Substituents Control Excited-State Decay Kinetics in Red-Phosphorescent Platinum Complexes.

Achieving high-efficiency red phosphorescence remains a significant challenge, especially in cyclometalated platinum complexes where radiative rates are inherently slower than their iridium counterparts. In this work, six red-emitting cyclometalated platinum complexes of the formula Pt(C∧N)[(Ar)acNac] (C∧N is the cyclometalating ligand, and (Ar)acNac is an aryl-substituted β-ketoiminate ancillary ligand) were synthesized and characterized. Two C∧N ligands were employed, 1-phenylisoquinoline (piq) and its cyano-substituted analogue 1-phenylisoquinoline-4-carbonitrile (piqCN), which both result in red phosphorescence in cyclometalated platinum complexes. These were paired with three (Ar)acNac ligands that are sterically differentiated via the N-aryl group, which is phenyl in the unsubstituted analogue (Ph)acNac and 2,6-dimethylphenyl or 2,6-diisopropylphenyl in the sterically encumbered analogues. An in-depth photophysical analysis of all compounds was performed and compared to the related compounds with the acetylacetonate (acac) ancillary ligand. While quantum yields are modest in the unsubstituted (Ph)acNac complexes, steric bulk on the β-ketoiminate has a pronounced effect on the excited-state dynamics and can lead to photoluminescence quantum yields of more than 0.50 in both solution and transparent polymer films, with the photoluminescence λmax ∼ 630 nm. We show that both steric effects on the electron-rich β-ketoiminate ancillary ligands and the cyano substituent on the cyclometalating ligand play a role in achieving high-efficiency phosphorescence in the red region.

Achieving Near-Infrared Phosphorescence Supramolecular Hydrogel Based on Amphiphilic Bromonaphthalimide Pyridinium Hierarchical Assembly.

Phosphorescent supramolecular hydrogels are currently a prevalent topic for their great promise in various photonic applications. Herein, an efficient near-infrared (NIR) phosphorescence supramolecular hydrogel is reported via the hierarchical assembly strategy in aqueous solution, which is fabricated from amphiphilic bromonaphthalimide pyridinium derivative (G), exfoliated Laponite (LP) nanosheets, and polymeric polyacrylamide (PAAm). Initially, G spontaneously self-aggregates into spherical nanoparticles covered with positively charged pyridinium units and emits single fluorescence at 410nm. Driven by electrostatic interactions with negatively charged nanosheets, the nanoparticles subsequently function as the cross-linked binders and coassemble with LP into supramolecular hydrogels with an engendered red room-temperature phosphorescence (RTP) up to 620nm. Benefiting from hydrogen-bonding interactions-mediated physical cross-linkage, the further introduction of PAAm not only significantly elevates the mechanical strength of the hydrogels showing fast self-healing capability, but also increases phosphorescence lifetime from 2.49to 4.20ms, especially generating phosphorescence at even higher temperature (τ 363 K = 2.46ms). Additionally, efficient RTP energy transfer occurs after doping a small amount of organic dye heptamethine cyanine (IR780) as an acceptor into hydrogels, resulting in a long-lived NIR emission at 823nm with a high donor/acceptor ratio, which is successfully applied for cell labeling in the NIR window.

Dual Fluorescence and Phosphorescence Emissions from Dye-Modified (NCN)-Bismuth Pincer Thiolate Complexes.

We report the synthesis, characterization, and photophysical properties of four new dye-modified (NCN)Bi pincer complexes with two mercaptocoumarin or mercaptopyrene ligands. Their photophysical properties were probed by UV/vis spectroscopy, photoluminescence (PL) studies, and time-dependent density functional theory (TD-DFT) calculations. Absorption spectra of the complexes are dominated by mixed pyrene or coumarin π → π*/n(pS) → pyrene or coumarin π* transitions. While unstable toward reductive elimination of the corresponding disulfide under irradiation at room temperature, the complexes provide stable emissions at 77 K. Under these conditions, coumarin complexes 2 and 4 exhibit exclusively green phosphorescence at 508 nm. In contrast, the emissive properties of pyrene complexes 1 and 3 depend on the excitation wavelength and on sample concentration. Irradiation into the lowest-energy absorption band exclusively triggers red phosphorescence from the pyrenyl residues at 640 nm. At concentrations c < 1 μM, excitation into higher excited electronic states results in blue pyrene fluorescence. With increasing c (1-100 μM), the emission profile changes to dual fluorescence and phosphorescence emission, with a steady increase of the phosphorescence intensity, until at c ≥ 1 mM only red phosphorescence ensues. Progressive red-shifts and broadening of steady-state excitation spectra with increasing sample concentration suggest the presence of static excimers, as we observe it for concentrated solutions of pyrene. Crystalline and powdered samples of 1 indeed show intermolecular association through π-stacking. TD-DFT calculations on model dimers and a tetramer of 1 support the idea of aggregation-induced intersystem crossing (AI-ISC) as the underlying reason for this behavior.

Phosphorescent PdII-PdII Emitter-Based Red OLEDs with an EQEmax of 20.52.

Three dinuclear Pd(II) complexes (1, 2, and 3) with intense red phosphorescence at room temperature are here synthesized using strong ligand field strength compounds. All three complexes are characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and elemental analyses. Complexes 2 and 3 are characterized by single-crystal X-ray diffraction. The crystalline data of 2 and 3 reveal complex double-layer structures, with Pd-Pd distances of 2.8690(9) Å and 2.8584(17) Å, respectively. Furthermore, complexes 1, 2, and 3 show phosphorescence at room temperature in their solid states at the wavelengths of 678, 601, and 672nm, respectively. In addition, they show phosphorescence at 634, 635, and 582nm, respectively, in the 2wt.% (PMMA) films, and phosphorescence at 670, 675, and 589nm, respectively, in the deoxygenated CH2Cl2 solutions. Among three complexes, complex 1 shows red emission at 634nm with phosphorescent quantum yield Ф = 67% in the 2wt.% PMMA film. Furthermore, complex 1-based organic light-emitting diode is fabricated using a vapor-phase deposition process, and their maximum external quantum efficiency reaches 20.52%, which is the highest percentage obtained by using the dinuclear Pd(II) complex triplet emitters with the CIE coordinates of (0.62, 0.38).

Effect of Red Emissive Ligand Number on Dendronized Solution‐Processable Iridium(III) Complexes for Organic Light‐Emitting Diodes

AbstractTris‐bidentate iridium(III) complexes used in organic light‐emitting diodes (OLEDs) are typically homoleptic or heteroleptic with three or two identical emissive ligands, respectively. Herein red phosphorescence emitting dendrimers composed of first generation biphenyl dendrons, 2‐ethylhexyloxy surface groups and an iridium(III) complex core with three, two or one emissive [4‐phenyl]−2‐[thiophen‐2‐yl]quinoline ligands are reported. The dendrimers have similar photoluminescence quantum yields (PLQYs) in solution (84–88%), neat film (23–25%) and when blended with tris(4‐carbazoyl‐9‐ylphenyl)amine (72–73%), enabling the effect of the number of emissive ligands on OLED performance to be determined. The external quantum efficiency (EQE) of OLEDs composed of neat dendrimer films increased with decreasing number of emissive ligands, with the device composed of the dendrimer having a single emissive ligand having an EQE of 9.2%, which is almost double that expected from a bottom emitting device and a film PLQY of 25 ± 3.6%. The emission is Lambertian and the higher‐than‐expected EQE is ascribed to alignment of the single emissive ligand being optimal for light‐outcoupling. The EQE of OLEDs containing the blend film also increased with decreasing emissive number of ligands (maximum EQE = 15.4%).

Insights into a New Multi‐Stimuli‐Responsive Photochromic Metal‐Organic Framework: Highly Sensitive Turn‐On Luminescence in a Lanthanum Phosphonate

AbstractThe new microporous metal organic framework [La2(H2O)5(H2TPPE)]·3H2O (CAU‐54), is obtained in a hydrothermal reaction of the linker 1,1,2,2‐tetrakis(4′‐phosphonophenyl)ethylene (H8TPPE) and La3+ ions. The extensive characterization including temperature‐dependent crystal structures and spectroscopic properties allowed to understand the unique, multi‐responsive material properties. CAU‐54 exhibits rarely observed reversible photochromism as well as turn‐on photoluminescence by various external chemical or physical stimuli including change of pressure, solvent exchange, and temperature variation. These properties can be unequivocally assigned to the presence of tetraphenylethylene (TPE) moieties of the linker molecules within the MOF, i.e., the ordered spatial arrangement of the linker molecules, the presence of accessible pores as well as the coordination flexibility of the phosphonate groups and the rotational freedom of the linker. By temperature‐dependent steady‐state and time‐resolved luminescence studies, it is shown that this compound exhibits a) blue fluorescence that becomes effectively quenched at room temperature, b) green efficient luminescence with thermal stability up to 400 K, and c) red phosphorescence correlated to the observed photochromism. In addition, CAU‐54 shows unusual thermal expansion properties as shown by temperature‐dependent powder X‐ray diffraction measurements with identified transition points that correlate with the observed temperature‐dependent changes in the photoluminescence.

Cyclometalated Iridium(III) Complexes Containing Viologen-Modified Phenylpyridine Ligands as Electroluminochromic Active Molecules for Information Display.

Electroluminochromic (ELC) materials have garnered significant research interest because of their potential applications in lighting, displaying, and sensing. These materials exhibit reversible modulation of photoluminescence under low-voltage stimuli. Here five phosphorescent iridium(III) complexes are reported featuring viologen-substituted 2-phenylpyridine (Vppy) ligands acting as electroactive components. Four of the complexes are bis-cyclometalated and coordinated with either neutral bipyridine derivatives or negatively charged 2-picolinate. The remaining complex is heteroleptic tris-cyclometalated, containing one Vppy and two 2-phenylquinoline ligands. Upon photoexcitation, the bis-cyclometalated complexes exhibit orange to red phosphorescence originating from mixed triplet metal-to-ligand charge transfer (3MLCT) and intraligand (3IL) dπ(Ir)/π(Vppy) → π*(Vppy) state, whereas the tris-cyclometalated complex is non-emissive due to a low Ir(IV/III) oxidation potential favoring oxidative quenching by the viologen pendants. When the cationic viologens are electrochemically reduced to their neutral form, the bis-cyclometalated complexes show a remarkable blue-shift in their phosphorescence maxima due to increased energy levels of the Vppy molecular orbitals. In the case of the tris-cyclometalated complex, reduction of the viologen groups interrupts the quenching process, leading to a luminescence turn-on. These complexes are used to develop ELC devices, which exhibit reversible luminescence response in terms of color or on-off switching under a low voltage of 2V.

Rigidity‐Enhanced Narrowband Iridium(III) Complexes with Finely‐Optimized Emission Spectra for Efficient Pure‐Red Electroluminescence

AbstractAttaining phosphorescent materials with narrowband emission is crucial for advancing wide‐color‐gamut organic light‐emitting diode (OLED). Herein, a rigid modification strategy is introduced for iridium(III) complexes to achieve the narrowband red emission with negligible 0–1 peak. By introducing the rigid indolo[3,2,1‐jk]carbazole (ICz) into the cyclometalated ligand, Ir(III) complexes, ICziq‐Ir and ICzqz‐Ir, exhibit pure red phosphorescence with emission peaks at 608 and 613 nm and full widths at half‐maximum (FWHMs) of 37 and 38 nm (0.12 and 0.13 eV) in toluene, respectively. Furthermore, the specific site modification of ICzqz‐Ir greatly suppresses the high‐frequency vibration of the structure, resulting in the narrowband photoluminescent spectrum close to the Gaussian distribution with superior color purity. The OLEDs utilizing ICziq‐Ir and ICzqz‐Ir demonstrate maximum external quantum efficiencies of 21.4 and 17.8% as well as mild efficiency roll‐off. Remarkably, the electroluminescence spectra exhibit similar narrowband red emission with FWHMs of 37 and 43 nm and CIE coordinates of (0.65, 0.35) and (0.66, 0.34), attesting to the excellent color purity of the phosphorescent OLEDs.

Anionic Hydrogen-Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone.

Tautomers coexisting in an equilibrium system have significant potential for regulating luminescent properties because of their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this study, it is found that hydrogen-bonded organic frameworks (HOFs) composed of Br- anions can effectively separate and stabilize two proton-transfer tautomers of triarylformamidinium bromide: namely, the nitrogen cation (BA-N) and carbon cation (BA-C). The BA-N crystal consisting of a dense anionic HOF and parallelly aligned organic cations exhibits green thermally activated delayed fluorescence and red room-temperature phosphorescence (RTP). The BA-C crystal contains acetone molecules that induce an antiparallel arrangement of the organic cations to form a loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, switching of the HOFs between BA-N and BA-C can be achieved through the uptake and release of acetone, thereby dynamically adjusting multiple luminescent properties. Consequently, the HOF crystals can be used for the highly sensitive and specific sensing of acetone with a detection limit of 66.74 ppm. This study not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with a sensitive response to a stimulus.