Crystallization-induced phosphorescence,remarkable mechanochromism,and grinding enhanced emission of benzophenone-aromatic amine conjugates

Twisted pure organic luminogens based on benzophenone and aromatic amines exhibit both fluorescence and phosphorescence in crystals, while owning merely red-shifted fluorescence at ground amorphous solids. Some of them even demonstrate greatly enhanced emission upon grinding.     

Polymorphism dependent triplet-involved emissions of a pure organic luminogen

Polymorphism has been frequently used in tuning the singlet emissions of pure organic dyes. The modulation of triplet-involved emissions, particularly room temperature phosphorescence(RTP),however, is scarcely reported. Herein, polymorphism is reported to tune the triplet-involved emissions of 2 CZBZL, a newly designed pure organic luminogen consisting of twisted benzil and two planar carbazole moieties. Other than the conventional modulation through changing molecular conformation and packing, vibration can also finely tune the triplet-involved emissions. Besides prompt fluorescence(PF),polymorph B with relatively extended conformation emits thermally activated delayed fluorescence(TADF), whereas the others(A, C–E) with similarly more twisted conformations generate predominant RTP or simultaneous DF and RTP. These results demonstrate the fascinating chance to regulate the tripletinvolved emissions through controlling conformation and vibration.     

Subtle structure tailoring of metal-free triazine luminogens for highly efficient ultralong organic phosphorescence

Highly efficient ultralong organic phosphorescence (UOP) based on a series of metal-free triazine luminogens was achieved via subtly structural tailoring of bromine substituted positions.Impressively,p-BrAT in solid state displayed high phosphorescence efficiency up to 9.7% with a long lifetime of 386 ms,which was one of the highest efficient UOP materials reported so far in metal-free compounds.     

Recent progress on pure organic room temperature phosphorescence materials based on host-guest interactions

The inclusion of specific organic phosphorescent guest molecules by the host molecules can reduce the nonradiative transitions and engender room temperature phosphorescence emission.     

Recent progress on pure organic room temperature phosphorescence materials based on host-guest interactions

Pure organic room temperature phosphorescence (RTP) has been attracting a lot interest recently. So far, many strategies have succeeded in achieving efficient organic RTP materials by increasing the rate of intersystem crossing (ISC) and suppressing non-radiative transitions. In supramolecular chemistry, the control and regulation of molecular recognition based on the role of the host and guest in supramolecular polymers matrix, has attracted much attention. Recently, researchers have successfully achieved room temperature phosphorescence of pure organic complexes through host-guest interactions. The host molecule specifically includes the phosphorescent guest to reduce non-radiative transitions and enhance room temperature phosphorescence emission. This review aims to describe the developments and achievements of pure organic room temperature phosphorescence systems through the mechanism of host-guest interactions in recent years, and demonstrates the exploration and pursuit of phosphorescent materials of researchers in different fields.     

Subtle structure tailoring of metal-free triazine luminogens for highly efficient ultralong organic phosphorescence

Ultralong organic phosphorescent materials have invoked considerable attention for their great potential in sensing, data encryption, information anti-counterfeiting and so forth. However, effective ways to achieve highly efficient ultralong organic phosphorescence (UOP) in metal-free organic materials remain a great challenge. Herein, we designed three isomers based on asymmetric triazines with various bromine substituted positions. Impressively, phosphorescence efficiency of p-BrAT in solid state can reach up to 9.7% with a long lifetime of 386 ms, which was one of the highest efficient UOP materials reported so far. Theoretical calculations further demonstrated that para-substitution exhibited the most effective radiative transition for triplet excitons. These results will provide an effective approach to achieving highly efficient UOP materials.     

Achieving room temperature phosphorescence from organic small molecules on amino acid skeleton

Room temperature phosphorescence (RTP) generated by small molecules has attracted great attention due to their unique potentials for biosensor, bioimaging and security protection. While, the design of RTP materials is extremely challenging for organic small molecules in non-crystalline solid state. Herein, we report a new strategy for achieving non-crystalline organic small molecules with RTP emission by modifying different phosphors onto diphenylalanine or phenylalanine derivatives. Benefiting from the skeletal structure of the amino acid derivatives, there are intermolecular hydrogen bond formation and rigidification effect, thereby minimizing the intermolecular motions and enhancing their RTP performance     

Effect of small organic molecules on room temperature phosphorescence properties of naphthol ternary inclusion complexes in β-cyclodextrin

The influence of nine small organic molecules on the phosphorescence properties of β-cyclodextrin (β-CD)/1-naphthol/1,2-dibromoethane (DBE) and β-CD/2-naphthol/DBE ternary inclusion complexes are examined by means of room temperature phosphorescence (RTP) measurements. It was demonstrated that the rigidity of β-CD/naphthol inclusion complex, RTP intensity and lifetime could be enhanced when different small organic molecules (less than 1% v/v) were added respectively; the analytical characters of two kinds of naphthols in host-guest stabilized-RTP were improved. The linear range of 1-naphthol become broad in the presence of n-propanol, methanol, ethanol or 2-propanol and its detection limit was reduced from 4×10⁻⁶ to 7.5×10⁻⁸ mol l⁻¹ in the presence of 0.6% (v/v) methanol. Likewise, for 2-naphthol, the detection limit was reduced from 2.0×10⁻⁶ to 2.8×10⁻⁷ mol l⁻¹ and to 8.1×10⁻⁷ mol l⁻¹ after 0.5% (v/v) glycol and 0.2% (v/v) 2-propanol being added, respectively.     

Achieving room temperature phosphorescence from organic small molecules on amino acid skeleton

Room temperature phosphorescence (RTP) generated by small molecules has attracted great attention due to their unique potentials for biosensor, bioimaging and security protection. While, the design of RTP materials is extremely challenging for organic small molecules in non-crystalline solid state. Herein, we report a new strategy for achieving non-crystalline organic small molecules with RTP emission by modifying different phosphors onto diphenylalanine or phenylalanine derivatives. Benefiting from the skeletal structure of the amino acid derivatives, there are intermolecular hydrogen bond formation and rigidification effect, thereby minimizing the intermolecular motions and enhancing their RTP performance     

Direct screening of tetracyclines in water and bovine milk using room temperature phosphorescence detection

A fast and simple flow-through optosensor was designed and characterized for the direct screening of four tetracycline (TCC) antibiotics (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in water and bovine milk samples. The proposed optosensor provides rapid binary yes/no overall responses, being appropriate for the screening of this family of antibiotics above or below a pre-set concentration threshold.The experimental set-up is based on a flow-injection manifold coupled on-line to a phosphorescence detector. Aliquots of the samples are pretreated with Eu(III) to form room temperature phosphorescent metal chelates and injected in the flow manifold. Those chelates are then on-line retained on a conventional flow-cell (packed with polymeric Amberlite XAD-4 particles) which is placed inside the cell holder of the phosphorimeter. After the emission is registered, the antibiotic-metal complexes are eluted from the packed resin with 1 M HCl (for milk samples a second regeneration step, using methanol, should be performed). A sample throughput of about 20 samples per hour was obtained. Optimum experimental conditions include a pH 9, a Eu(III) concentration of 2 × 10⁻⁴ M and 8 mM sodium sulphite as chemical deoxygenant. The phosphorescence emitted by the europium-TCC complexes was measured at 394 and 617 nm for excitation and emission wavelengths, respectively.The unreliability region, given by the probability of false positives and false negatives, respectively (set at 5% in both cases) was in the range between 0.2 and 11.6 nМ for detection of tetracyclines in water samples (at a cut-off level of 4 nM) and in the range between 165 and 238 nM for detection of tetracyclines in milk (cut-off level fixed at the normative EU level of 200 nM). Finally, the applicability of the proposed screening optosensor was tested for the reliable control of tetracyclines in contaminated and uncontaminated water and milk samples.     

Room-temperature phosphorescence from purely organic materials

Room-temperature phosphorescence (RTP) materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes. In this short review, recent progress on enhancement of RTP from purely organic materials is summarized. According to the mechanism of phosphorescence emission, two principles are discussed to construct efficient RTP materials: one is promoting intersystem crossing (ISC) efficiency by using aromatic carbonyl, heavyatom, or/and heterocycle/heteroatom containing compounds; the other is suppressing intramolecular motion and intermolecular collision which can quench excited triplet states, including embedding phosphors into polymers and packing them tightly in crystals. With aforementioned strategies, RTP from purely organic materials was achieved both in fluid and rigid media.     

Metal nanoparticle-enhanced room temperature phosphorescence of diiodofluorescein on the filter paper substrate

<正>Metal-enhanced room temperature phosphorescence of diiodofluorescein was first observed on filter paper surface.The phosphorescence intensity is 2.5-fold brighter from diiodofluorescein on silver nanoparticles-deposited filter paper as compared with an identical control sample without silver nanoparticles.Furthermore,enhanced absorption was also observed for the same system.Our findings suggest that both singlet and triplet states can couple to surface plasmons and enhance phosphorescence quantum yields at room temperature,as well as to increase the excitation rate of lumophores at room temperature.     

Stopped-flow determination of dipyridamole in pharmaceutical preparations by micellar-stabilized room temperature phosphorescence

The stopped flow mixing technique has been used to study the kinetic determination of dipyridamole by means of micellar-stabilized room temperature phosphorescence (RTP). This mixing system diminishes the time required for the deoxygenation of the micellar medium by sodium sulfite. The phosphorescence enhancers thallium (I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity and selectivity. A pH value of 10.6 was selected as adequate for phosphorescence development. The kinetic curve of dipyridamole phosphorescence was scanned at λ_ex=303 nm and λ_em=616 nm. Then, the intensity at 10 s, and the maximum slope of phosphorescence development, for an interval time of 1 s, were measured. Two determination approaches: intensity and rate methods, were proposed. The calibration graphs were linear for the concentration range from 50 to 400 ng ml⁻¹. The detection limits, according to Clayton et al., Anal. Chem. 59 (1987) 2506, were 21.5 and 37.5 ng ml⁻¹, for intensity and initial rate measurements, respectively. By applying the error propagation theory, the detection limits were 19.0 and 33.0 ng ml⁻¹, for intensity and initial rate measurements, respectively. Two commercial formulations (persantin and asasantin) were analyzed by both proposed methodologies. Adequate recovery values were obtained in both cases.     

H-aggregation of cationic palladium-porphyrin as a function of anionic surfactant studied using phosphorescence, absorption and RLS spectra

Room temperature phosphorescence (RTP) was used as a useful analytical tool to investigate the interaction behavior between tetracationic meso-tetrakis (4-trimethylaminophenyl) porphyrin palladium (Pd-TAPP) and anionic sodium dodecyl sulfate (SDS). UV-vis absorption and resonance light scattering (RLS) were further applied to characterize the system. It was presumably suggested that nonspecific self-aggregates among porphyrins formed considering the relatively high concentration of Pd-TAPP. Furthermore, Pd-TAPP changed from free monomer/nonspecific aggregate to H-aggregate and then to out-micellized monomer/nonspecific aggregate as a function of SDS concentration. The fact that RTP signal enhanced obviously and excitation spectrum was blue-shifted by 1580cm(-1) in energy with respect to energy of free Pd-TAPP monomer demonstrated that 1:4 electrostatic interaction between Pd-TAPP and SDS led to the formation of the premicellar porphyrin-surfactant H-aggregates. The RLS spectrum reviewed that the formed H-aggregates were multiple porphyrin units, and UV-vis spectra revealed that cationic groups of monomers/nonspecific aggregates of Pd-TAPP were electrostatically attracted in favor of the surface of anionic micelles but were not encapsulated within apolar regions of SDS micelles when the concentration of SDS was above its critical micelle concentration (CMC).     

Promoting organic room temperature phosphorescence through in situ polymerization

Organic room temperature phosphorescence materials (RTP) have attracted much attention for their wide application in organic light-emitting diodes, anti-counterfeiting, and sensors. In this work, a series of organic luminogens containing carbonyl and aromatics were fixed in a three-dimensional polymethyl methacrylate (PMMA) network by in situ polymerization. All organic luminogens-doped in situ PMMA (s-PMMA) columns achieved longer RTP lifetimes than those of doped commercial PMMA (c-PMMA) films, especially, the RTP lifetime of NMP2O in these PMMA matrixes increased from 1.82 ms to 156.34 ms by about 86 times. It is mainly due to the restriction of molecular motions by highly entangled polymer chains and rigid environments to efficiently inhibit the non-radiative transitions. Also, the excellent shielding effect toward oxygen by the in situ polymerization process can avoid possible quenching effects on triplet excited states, beneficial to RTP emission. Thus, it affords an efficient approach to achieving persistent RTP for three-dimensional displaying applications.     

Simplex optimization and kinetic determination of nabumetone in pharmaceutical preparations by micellar—stabilized room temperature phosphorescence

The present method described the kinetic determination of nabumetone, a non-steroidal anti-inflammatory drug, by means of micellar-stabilized room temperature phosphorescence (MS-RTP), using the stopped-flow mixing technique. This methodology enables us to determine analytes in complex matrices without the need for a tedious separation process, as well as greatly diminishes the time for the analysis.Firstly, chemical and instrumental variables affecting the rate of phosphorescent development and the intensity of the signal, were found using a simplex optimization procedure. As application, nabumetone was determined in commercial Spanish pharmaceutical preparations.With the proposed method, the maximum signal of phosphorescence appears in only 10 s once the sample has been prepared, and the maximum slope of the kinetic curve, corresponding with the maximum rate of the phosphorescence development, was measured at λ_ex = 271 nm and λ_em = 520 nm. The overall least-squares regression to find the straight line that fitted the experimental data, the detection limit, the repeatability and the standard deviation for replicate sample, were also determined.The proposed method was validated versus a HPLC method with satisfactoty results.     

pH-Responsive amorphous room-temperature phosphorescence polymer featuring delayed fluorescence based on fluorescein

Numerous researchers have paid attention to achieve metal-free phosphorescence by exploring new structures or new mechanisms. Herein, a facile way is introduced to endow a common fluorescence dye, tetrabromofluorescein (4Br-Flu), some fabulous optical characteristics such as dual emission including thermally activated delayed fluorescence, room-temperature phosphorescence (RTP), and the excellent pH-sensitivity. Shortly, 4Br-Flu with good light-emitting properties is composed into the polymer system. The multiple bromine atoms promote the spin-orbit coupling effect and facilitate triplet excitation. Especially, the hydrogen bonding network of the polymer restricts the molecular motion of 4Br-Flu so that the system can emit long-wavelength RTP when 4Br-Flu is doped into polyvinyl alcohol or co-polymerized with acrylamide. Due to the reversible transformation of protonation and deprotonation, the 4Br-Flu based polymer responded to acid and alkali like a phosphorescent switch which makes it an excellent hydrogen chloride/ammonia gas leak detector in dry environment.     

荧光/磷光混合型白光有机发光二极管的研究

白光有机发光二极管（white organic light-emitting diodes,WOLEDs）在全色显示、固态照明以及背光源等领域有巨大的应用前景,其研究备受关注.其中,荧光/磷光混合型WOLEDs因兼具荧光材料的长寿命和磷光材料的高效率,被认为是目前最有希望实现照明应用的器件结构.荧光/磷光混合型WOLEDs最重要的问题是要解决荧光材料的单线态激子和磷光材料的三线态激子的协同发光.为了避免单线态激子和三线态激子的相互猝灭问题,必须设计有效的器件结构.本文以两种不同三线态能级的蓝光荧光材料为研究对象,介绍了不同高性能荧光/磷光混合型WOLEDs的结构设计与性能.研究表明,载流子传输平衡的高效结构设计和激子分布宽范围内的有效调控是实现高性能荧光/磷光混合型WOLEDs的关键.     

Determination of trace levels of mercury in water samples based on room temperature phosphorescence energy transfer

A novel method has been developed for the sensitive determination of mercury in aqueous media by room temperature phosphorescence (RTP). The measurement principle is based on the energy transfer (ET) from a phosphor molecule (acting as a donor) to a Hg-sensitive dye (acceptor). To our acknowledgment this is the first RTP method for mercury measurement developed so far. α-Bromonaphthalene (BrN) was selected as the phosphorescent donor molecule (BrN can produce significant RTP emission in aqueous media in a β-cyclodextrin rigid microenvironment without deoxygenation).The absorption spectrum of the complex formed between mercury and the dithizone dye possesses a desirable spectral overlap with the RTP emission spectrum of the donor (BrN), giving rise to a nonradiative ET from the phosphor molecules to the mercury complex. An increase in the concentration of Hg(II) causes an increase on the concentration of the dithizone complex (acceptor) with the subsequent increase of the absorbance and, therefore, resulting in a decrease of the RTP emission. Both, RTP intensities and triplet lifetimes of the BrN decreased with increases on the Hg(II) concentration.Possible interferences present in natural waters, including different cations and anions, which could affect the analytical response, were evaluated and the analytical performance characteristics investigated. The use of phosphorescence measurements (low background noise signals) resulted in an improvement on the sensitivity of the Hg(II) detection higher than five times as compared to the molecular absorption spectrophotometric method for Hg(II) detection based on dithizone as Hg-indicator. A detection limit (D.L.) of 14 ng ml⁻¹ of Hg(II) was obtained by RTP with a precision of ±4.8% for five replicates of 300 ng ml⁻¹ of Hg(II). The usefulness of the method was successfully evaluated by the determination of Hg(II) in spiked natural water samples.     

Novel self-protective phosphorescence from crystalline nanoparticles assembled by 3-bromo- and 3-iodo-carbazoles based on halogen-halogen interaction in suspension solutions

The crystalline nanoparticles can be assembled by 3-bromo- and 3-iodo-carbazole (3-BrC and 3-IC) based on the halogen-halogen interaction in suspension aqueous solutions. As the colloid-like suspension was dropped onto film the particles further aggregate as rod-like structures with size of 3 μm in length and 1 μm in width. The halogen-halogen interaction are well proved by single crystal X-ray data, and the data reveal that each bromine atom interacts with the neighboring two, and each iodine atom interacts with the neighboring five and I-I interaction is stronger than that of Br-Br. Both 3-BrC and 3-IC can emit novel self-protective room temperature phosphorescence (RTP) in the range of 480 to near 800 nm at the excitation of 338 nm, and 3-BrC shows additionally the delayed fluorescence emission from 350 to 480 nm, both possessing the charge-transfer character caused by halogenations. RTP decay possesses the bi-exponential property and RTP lifetimes are 3.37, 31.16 ms (with ethanol) and 1.52, 30.83 ms (with THF) for 3-BrC or 3.53, 14.95 ms (with ethanol) and 1.68 ms, 13.74 ms (with THF) for 3-IC, showing “ heavier atom ”, I, makes intersystem crossing rate k_ISC from both S₁ to T₁ and T₁ to S₀ faster. For the results, the detection limits of 3-BrC and 3-IC can reach 2.4 × 10⁻⁷ and 9.0 × 10⁻⁸ mol L⁻¹, respectively, with wider linear range and higher precision compared with other systems.