Phosphorescence Quantum Yield Research Articles

Side group dependent room temperature crystallization-induced phosphorescence of benzil based all organic phosphors.

In this work, we report alkoxy substituted benzil based all organic room temperature phosphors which showed crystallization induced phosphorescence (CIP). Nine title compounds were prepared with various alkyl lengths (OCnH2n+1: n = 8-16) and the effect of alkyl side group length on the phosphorescence performance was investigated, as compared to p-anisil. It was found that both phosphorescence quantum yield and lifetime increased concomitantly as the alkyl length increased up to nonyloxy (BZL-OC9). Further increase in the carbon number caused the phosphorescence performance to deteriorate due to greater conformational freedom of the side groups. An incredible quantum yield of 70% was achieved for BZL-OC9. A promising finding is that the increased quantum yield was accompanied by the increase in the lifetime relative to p-anisil, which has been historically challenging. Single crystallography coupled with UV-Vis spectroscopy revealed that a higher level of intermolecular π-π interactions was observed from p-anisil while more alkyl interactions with less intermolecular π-orbital overlap were found for BZL-OC8. As a result, molecular rigidification with less phosphorescence quenching was achieved for BZL-OC8 leading to enhanced performance. A precipitation study on a dichloromethane solution as a function of the content of MeOH (poor solvent) proved that the emission of the BZL-OCn system is truly aggregation-induced. The current work demonstrates that strategic side group engineering could be a promising approach to developing high-performance all organic phosphors as well as improving the properties of existing phosphors.

Molecular phosphorescence enhancement by the plasmon field of metal nanoparticles.

A theoretical model is proposed that allows the estimation of the quantum yield of phosphorescence of dye molecules in the vicinity of plasmonic nanoparticles. For this purpose, the rate constants of the radiative and nonradiative intramolecular transitions for rhodamine 123 (Rh123) and brominated rhodamine (Rh123-2Br) dyes have been calculated. The plasmon effect of Ag nanoparticles on various types of luminescence processes has been studied both theoretically and experimentally. We show that in the presence of a plasmonic nanoparticle, the efficiency of the immediate and delayed fluorescence increases significantly. The phosphorescence rate of the rhodamine dyes also increases near plasmonic nanoparticles. The long-lived luminescence i.e., delayed fluorescence and phosphorescence is more enhanced for Rh123-2Br than for Rh123. The largest phosphorescence quantum yield is obtained when the dye molecule is at a distance of 4-6 nm from the nanoparticle surface. Our results can be used in the design of plasmon-enhancing nanostructures for light-emitting media, organic light-emitting diodes, photovoltaic devices, and catalysts for activation of molecular oxygen.

Photophysical properties of Pt(ii) complexes based on the benzoquinoline (bzq) ligand with OLED implication: a theoretical study.

In this study, we investigate photophysical properties of eight inorganic Pt(ii) complexes containing the bzq (benzoquinoline) ligand for OLED applications using high-level density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. We explore the radiative and non-radiative relaxation constants (k r, k nr), spin-orbit coupling (SOC) matrix elements, and spectral properties. To ensure compatibility between the host and guest compounds, we determine the HOMO and LUMO energy levels, as well as the triplet excitation energies of the selected systems, and evaluate their efficiency for OLED devices. Our findings indicate that all systems, except for 2a and 2b, exhibit a small S1-T1 energetic gap (ΔE ≤ 0.60 eV) and promising SOC matrix elements (25-93 cm-1), leading to a significant intersystem crossing (ISC) process. These complexes also show promising radiative relaxation rates (k r = ∼10-4 s-1) and high phosphorescent quantum yields (Φ > 30%). Thus, our results confirm that six out of the eight selected Pt(ii) complexes are promising candidates for use in the emitting layer (EML) of OLED devices as efficient green emitters.

Construction of a tetrabenzotetrathia[8]circulene by a "fold-in" oxidative fusion reaction: synthesis and optical properties.

Herein we report the first synthesis of a tetrabenzotetrathia[8]circulene by a "fold-in" type oxidative fusion reaction. Compared to the pristine tetrathia[8]circulene, the four-fold benzoannulation slightly weakened the antiaromatic character of the central COT ring. The tetrabenzotetrathia[8]circulene exhibited fluorescence at room temperature, and phosphorescence at 77 K with a phosphorescence quantum yield of 11.7%.

Achieving pure room temperature phosphorescence (RTP) in phenoselenazine-based organic emitters through synergism among heavy atom effect, enhanced n → π* transitions and magnified electron coupling by the A-D-A molecular configuration.

The weak spin-orbit coupling (SOC) in metal-free organic molecules poses a challenge in achieving phosphorescence emission. To attain pure phosphorescence in RTP organic emitters, a promising molecular design concept has been proposed. This involves incorporating n → π* transitions and leveraging the heavy atomic effect within the spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) mechanism of bipolar molecules. Following this design concept, two bipolar metal-free organic molecules (PhSeB and PhSeDB) with donor-acceptor (D-A) and acceptor-donor-acceptor (A-D-A) configurations have been synthesized. When the molecular configuration changes from D-A to A-D-A, PhSeDB exhibits stronger electron coupling and n → π* transitions, which can further enhance the spin-orbit coupling (SOC) together with the heave atom effect from the selenium atom. By the advanced synergism among enhanced n → π* transitions, heavy atom effect and magnified electron coupling to efficiently promote phosphorescence emission, PhSeDB can achieve pure RTP emission in both the solution and doped solid film. Thanks to the higher spin-orbit coupling matrix elements (SOCMEs) for T1 ↔ S0, PhSeDB attains the highest phosphorescence quantum yield (ca. 0.78) among all the RTP organic emitters reported. Consequently, the purely organic phosphorescent light-emitting diodes (POPLEDs) based on PhSeDB achieve the highest external quantum efficiencies of 18.2% and luminance of 3000 cd m-2. These encouraging results underscore the significant potential of this innovative molecular design concept for highly efficient POPLEDs.

Cationic Porphyrin-Based Ionic Nanomedicines for Improved Photodynamic Therapy.

This study presents the synthesis and characterization of monosubstituted cationic porphyrin as a photodynamic therapeutic agent. Cationic porphyrin was converted into ionic materials by using a single-step ion exchange reaction. The small iodide counteranion was replaced with bulky BETI and IR783 anions to reduce aggregation and enhance the photodynamic effect of porphyrin. Carrier-free ionic nanomedicines were then prepared by using the reprecipitation method. The photophysical characterization of parent porphyrin, ionic materials, and ionic nanomaterials, including absorbance, fluorescence and phosphorescence emission, quantum yield, radiative and nonradiative rate, and lifetimes, was performed. The results revealed that the counteranion significantly affects the photophysical properties of porphyrin. The ionic nanomaterials exhibited an increase in the reactive oxygen yield and enhanced cytotoxicity toward the MCF-7 cancer cell line. Examination of results revealed that the ionic materials exhibited an enhanced photodynamic therapeutic activity with a low IC50 value (nanomolar) in cancerous cells. These nanomedicines were mainly localized in the mitochondria. The improved light cytotoxicity is attributed to the enhanced photophysical properties and positive surface charge of the ionic nanomedicines that facilitate efficient cellular uptake. These results demonstrate that ionic material-based nanodrugs are promising photosensitizers for photodynamic therapy.

Chiral‐Guest Induced Multicolor‐Tunable Circularly Polarized Room Temperature Phosphorescence

AbstractThe development of organic circularly polarized room temperature phosphorescence (CP‐RTP) materials with tunable emission colors has important value in the field of optoelectronic applications but remains a challenging issue. Herein, a CP‐RTP doped system with green, yellow, and red afterglow is constructed by introducing chiral groups into three phosphors naphthalene, phenanthrene, and pyrene as guests respectively, using polyvinyl pyrrolidone (PVP) as the host. The phosphorescence quantum yield of the doped system is 7.3%–13.6%, the phosphorescence lifetime is 341 ms–1017 ms, and the asymmetry factor is 0.001–0.0021. Further doping three guests simultaneously into the PVP resulted in the four‐component doped materials. Benefiting from the different excitation wavelengths of three guests, when the excitation wavelength changes from 300 to 365 nm, the afterglow of the four‐component doped materials changes from green to yellow and finally to red. Moreover, due to the different phosphorescence lifetimes of different guests, the afterglow can in turn change from red to green after excitation at 365 nm, demonstrating a time‐dependence phosphorescence emission property. This doped strategy provides an effective platform for constructing organic multicolor CP‐RTP materials.

Stepwise taming of triplet excitons via multiple confinements in intrinsic polymers for long-lived room-temperature phosphorescence

Polymeric materials exhibiting room temperature phosphorescence (RTP) show a promising application potential. However, the conventional ways of preparing such materials are mainly focused on doping, which may suffer from phase separation, poor compatibility, and lack of effective methods to promote intersystem crossing and suppress the nonradiative deactivation rates. Herein, we present an intrinsically polymeric RTP system producing long-lived phosphorescence, high quantum yields and multiple colors by stepwise structural confinement to tame triplet excitons. In this strategy, the performance of the materials is improved in two aspects simultaneously: the phosphorescence lifetime of one polymer (9VA-B) increased more than 4 orders of magnitude, and the maximum phosphorescence quantum yield reached 16.04% in halogen-free polymers. Moreover, crack detection is realized by penetrating steam through the materials exposed to humid surroundings as a special quenching effect, and the information storage is carried out by employing the Morse code and the variations in lifetimes. This study provides a different strategy for constructing intrinsically polymeric RTP materials toward targeted applications.

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.

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.

Luminescence of In(III)Cl-etioporphyrin-I.

The luminescent and photophysical properties of the etioporphyrin-I complex with indium(III) chloride, InCl-EtioP-I were experimentally studied at room and liquid nitrogen temperatures in pure and mixed toluene solutions. At 77 K, in a 1:2 mixture of toluene with diethyl ether, the quantum yield of phosphorescence reaches 10.2%, while the duration of phosphorescence is 17 ms. At these conditions, the ratio of phosphorescence-to-fluorescence integral intensities is equal to 26.1, which is the highest for complexes of this type. At 298 K, the quantum yield of the singlet oxygen generation is maximal in pure toluene (81%). Quantum-chemical calculations of absorption and fluorescence spectra at temperatures of 77 K and 298 K qualitatively coincide with the experimental data. The InCl-EtioP-I compound will further be used as a photoresponsive material in thin-film optoelectronic devices.

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.

Enhancing blue phosphorescence in matrix-free carbon dots through covalent crosslinking

Room temperature phosphorescence (RTP) of carbon dots (CDs) has received extensive attention due to its excellent performance and promising application. Here, a novel kind of matrix-free CDs with blue phosphorescence emission was synthesized by a simple one-step hydrothermal method of heating (3-Aminopropyl) trimethoxysilane (APTMS) and phosphoric acid in aqueous solution. The obtained CDs show a phosphorescence lifetime of 315.73 ms, and the absolute photoluminescence quantum yield (PLQY) and the phosphorescence quantum yield (PQY) can reach up to 37.8 % and 12.4 %, respectively. From the experimental results, we speculate that the generation of RTP is attributed to the restriction effect of the covalent crosslinking structure of SiOSi, SiOC, or SiC bonds formed on the CDs surface. In addition, phosphoric acid as a crosslinking agent and heteroatom dopant can promote the formation of cross-linked structures and facilitate the intersystem crossing (ISC) process, thus enhancing room temperature phosphorescence. Finally, the CDs were successfully used in information encryption and anti-counterfeiting.

Photophysical properties of Radachlorin photosensitizer in solutions of different pH, viscosity and polarity

We present a thorough experimental investigation of fluorescence properties of Radachlorin photosensitizer in solutions of different acidity, viscosity and polarity. Experiments were performed using time-resolved fluorescence lifetime imaging and time-resolved analysis of polarized fluorescence. Variations of solution acidity resulted in considerable changes of Radachlorin fluorescence quantum yield and lifetime in the pH range from 4 to 7, but did not affect the rotational diffusion time, and almost did not change the quantum yield and characteristic times of singlet oxygen phosphorescence. Variations of solution polarity and viscosity were achieved by changing ethanol or methanol fraction in aqueous solution. The decrease of solution polarity resulted in nonlinear rise of Radachlorin fluorescence quantum yield and lifetime up to alcohol concentration of 50%–65%, as well as in considerable rise of singlet oxygen quantum yield and significant changes in characteristic times of its phosphorescence. Variations of solution viscosity resulted in changes of rotational diffusion time of Radachlorin molecules, which appeared to be in perfect correlation with methanol solution viscosity. Good correspondence with ethanol solution viscosity was observed only up to 50% alcohol fraction. Deviations of rotational diffusion time of Radachlorin molecules from direct proportionality with solution viscosity at higher ethanol concentrations were suggested to be due to different solvation conditions. The data obtained can give important reference points for analysis of microenvironment of Radachlorin molecules, their intracellular localization and performance in singlet oxygen generation.

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.

Achieving Stable and Switchable Ultralong Room-Temperature Phosphorescence from Polymer-Based Luminescent Materials with Three-Dimensional Covalent Networks for Light-Manipulated Anticounterfeiting.

Developing polymer-based organic afterglow materials with switchable ultralong organic phosphorescence (UOP) that are insensitive to moisture remains challenging. Herein, two organic luminogens, BBCC and BBCS, were synthesized by attaching 7H-benzo[c]carbazole (BBC) to benzophenone and diphenyl sulfone. These two emitters were employed as guest molecules and doped into epoxy polymers (EPs), which were constructed by in situ polymerization to achieve polymer materials BBCC-EP and BBCS-EP. It was found that BBCC-EP and BBCS-EP films exhibited significant photoactivated UOP properties. After light irradiation, they could produce a conspicuous organic afterglow with phosphorescence quantum yields and lifetimes up to 5.35% and 1.91 s, respectively. Meanwhile, BBCS-EP also presented photochromic characteristics. Upon thermal annealing, the UOP could be turned off, and the polymer films recovered to their pristine state, showing switchable organic afterglow. In addition, BBCC-EP and BBCS-EP displayed excellent water resistance and still produced obvious UOP after soaking in water for 4 weeks. Inspired by the unique photoactivated UOP and photochromic properties, BBCC and BBCS in the mixtures of diglycidyl ether of bisphenol A (DGEBA) and 1,3-propanediamine were employed as security inks for light-controlled multilevel anticounterfeiting. This work may provide helpful guidance for developing photostimuli-responsive polymer-based organic afterglow materials, especially those with stable UOP under ambient conditions.

Influence of Fluorinated Substituents on the Near-Infrared Phosphorescence of 5d Metallocorroles.

The influence of fluorinated substituents on the luminescent properties of rhenium-oxo, osmium-nitrido, and gold triarylcorroles was studied via a comparison of four ligands: triphenylcorrole (TPC), tris(p-trifluoromethylphenyl)corrole (TpCF3PC), tris{3,5-bis(trifluoromethyl)phenyl}corrole (T3,5-CF3PC), and tris(pentafluorophenyl)corrole (TPFPC). For each metal series examined, fluorinated substituents were found to enhance the luminescent properties, with the phosphorescence quantum yields and triplet decay times increasing in the order TPC < TpCF3PC < T3,5-CF3PC < TPFPC. Among the 11 complexes examined, the highest phosphorescence quantum yield, 2.2%, was recorded for Re[TPFPC](O).

Accessing blue-room-temperature phosphorescence from pyridine-fused extended coumarins

Coumarin derivatives have potential applications in sensing, laser dyes, fluorescent probes, and dye−sensitized solar cells due to their unique photophysical properties. However, the realization of room-temperature phosphorescence (RTP) under ambient conditions in coumarin derivatives remains unexplored. Extended coumarins can therefore be used to achieve RTP under ambient conditions. Here, we report two pyridine-fused coumarins (CPP, CPPCz); CPPCz contains a 9-phenyl carbazole unit that is covalently attached to the 5-position of CPP via a C–C single bond. Spectroscopic studies and quantum chemistry calculations reveal that CPPCz exhibits local emission (LE) and charge transfer (CT) emission in solution, while only LE emission is realized in CPP. In films, both compounds show fluorescence and blue-RTP under ambient conditions due to the low singlet-triplet gap (0.07–0.14 eV). The photoluminescence quantum yields are found to be 29–43%. Phosphorescence quantum yield was found to be 1.3–3%. This design principle reveals a method to understand RTP in extended coumarins.

Biocompatible Phosphorescent O2 Sensors Based on Ir(III) Complexes for In Vivo Hypoxia Imaging.

In this work, we obtained three new phosphorescent iridium complexes (Ir1-Ir3) of general stoichiometry [Ir(N^C)2(N^N)]Cl decorated with oligo(ethylene glycol) fragments to make them water-soluble and biocompatible, as well as to protect them from aggregation with biomolecules such as albumin. The major photophysical characteristics of these phosphorescent complexes are determined by the nature of two cyclometallating ligands (N^C) based on 2-pyridine-benzothiophene, since quantum chemical calculations revealed that the electronic transitions responsible for the excitation and emission are localized mainly at these fragments. However, the use of various diimine ligands (N^N) proved to affect the quantum yield of phosphorescence and allowed for changing the complexes' sensitivity to oxygen, due to the variations in the steric accessibility of the chromophore center for O2 molecules. It was also found that the N^N ligands made it possible to tune the biocompatibility of the resulting compounds. The wavelengths of the Ir1-Ir3 emission maxima fell in the range of 630-650 nm, the quantum yields reached 17% (Ir1) in a deaerated solution, and sensitivity to molecular oxygen, estimated as the ratio of emission lifetime in deaerated and aerated water solutions, displayed the highest value, 8.2, for Ir1. The obtained complexes featured low toxicity, good water solubility and the absence of a significant effect of biological environment components on the parameters of their emission. Of the studied compounds, Ir1 and Ir2 were chosen for in vitro and in vivo biological experiments to estimate oxygen concentration in cell lines and tumors. These sensors have demonstrated their effectiveness for mapping the distribution of oxygen and for monitoring hypoxia in the biological objects studied.