Aggregation-induced Phosphorescence Research Articles

Unusual Circularly Polarized and Aggregation-Induced Near-Infrared Phosphorescence of Helical Platinum(II) Complexes with Tetradentate Salen Ligands.

A series of chiral and helical PtII -Salen complexes with 1,1'-binaphthyl linkers were synthesized and characterized. Owing to the restriction of intramolecular motions of central 1,1'-binaphthyls, the complexes exhibit unusual near-infrared aggregation-induced phosphorescence (AIP). The (R)/(S) enantiopure complexes were characterized by X-ray diffraction, circular dichroism spectra, time-dependent density functional theory calculations, and circularly polarized luminescence (CPL). The present work explores the use of tetradentate ligands that can be easily prepared from commercially available enantiopure compounds, and the subsequent preparation of stable CPL-active square planar PtII complexes with AIP effect that may have interest in many applications.

Cyclometalated Platinum Complexes with Aggregation-Induced Phosphorescence Emission Behavior and Highly Efficient Electroluminescent Ability

Aggregation-induced emission (AIE) materials can exhibit intense luminescence in the aggregated or solid state, which are highly desirable for OLED application. However, only limited research results on developing AIE-active PtII complexes in electroluminescence (EL) application have been reported so far. Herein, a series of AIE-active PtII(C^N)(N-donor ligand)Cl complexes have been developed. Their chemical structures have been determined by NMR, MS, and X-ray crystallography characterization. Theoretical results including the frontier molecular orbitals, the simulated UV–vis spectra, and natural transition orbitals (NTO) have been employed to insightfully interpret their photophysical properties. It has also been found that a much higher degree of molecular aggregation in these PtII complexes should be required to induce phosphorescent AIE than that for the fluorescent AIE behavior. These AIE-active PtII complexes can exhibit very strong emission in poly(methyl methacrylate) (PMMA) films with the phosph...

Aggregation-induced phosphorescence enhancement of Mn-doped ZnS quantum dots: the role of dot-to-dot distance.

Assembled nanoparticles promote many applications in optics due to their instinct properties. The aggregation-induced phosphorescence enhancement (AIPE) of Mn-doped ZnS quantum dots (QDs) is widely used in biosensing, but the mechanism of such an enhancement is still unproven. This study explores the mechanism of the interesting finding of AIPE of Mn-doped ZnS QDs. To induce the aggregation of QDs, the method of electrostatic assembly was explored herein: negatively charged QDs were aggregated with protamine and positively charged QDs were aggregated with heparin. Using several ligands with hierarchical molecular weights for capping Mn-doped ZnS QDs, it was found that the AIPE of Mn-doped ZnS QDs was exponentially dependent on the dot-to-dot distance in aggregates. Together with detailed analysis of both the steady- and transient-state luminescence behaviors of Mn-doped ZnS QDs before and after aggregation, charge transfer from one dot (surface traps) to another (dopant bands) was identified as the driving factor for AIPE. Moreover, the d-band of the Mn2+ dopants was essential for the AIPE since it acts as the acceptor for the transferred charge from neighboring QDs. These conclusions can significantly contribute for better understanding of this interesting luminescence mechanism and future designing of the most suitable sensing systems.

The unsuspected influence of the pyridyl-triazole ligand isomerism upon the electronic properties of tricarbonyl rhenium complexes: an experimental and theoretical insight.

Two isomeric tricarbonyl rhenium(i) complexes, ReL1 and ReL2, that possess a 2-pyridyl-1,2,n-triazole (pyta) ligand (n = 4 and 3, respectively) connected to a 2-phenylbenzoxazole (PBO) moiety, were synthesized in good yields. The X-ray structures showed that in ReL1 the PBO moiety and the pyta ligand almost form a right angle hindering electron delocalization, while in ReL2 their nearly planar arrangement favors the electron delocalization in the whole organic ligand. Therefore, the nature of the ligand significantly influences the electron distribution in the two complexes, as indicated by the results of TD-DFT calculations. An electrochemical study highlighted that, by comparison with ReL2, the smaller HOMO-LUMO energy gap of ReL1 is in line with its lower first reduction potential. From a spectroscopic viewpoint, both complexes emitted phosphorescence in organic solvents, with distinct color and intensity. They also emitted in the solid state, but only ReL1 showed significant aggregation-induced phosphorescence emission (AIPE). This complete study sheds light on the crucial role of structural isomerism of the triazole group, which has been unsuspected for a long time although it can govern the geometry and electronic properties of rhenium complexes. It is shown for the first time that grafting a non-coordinated π-conjugated fragment on the N(4) atom of a 1,2,4-triazole group can be of high value for the design of efficient light-emitting materials based on rhenium complexes.

Aggregation-induced phosphorescence emission and pH recognition properties of an Iridium (III) complex

A novel Iridium (III) complex [Ir(ppy)2(Hppip)]PF6 (1) has been synthesized and characterized. The complex exhibits strong phosphorescence emission in high viscosity solvent glycerol and aggregation-induced phosphorescence emission in hexane solution. The high viscosity of glycerol and aggregation may restrict intramolecular rotation so that the compound exhibits stronger phosphorescence emission in glycerol and aggregated state. Compound 1 can also be a pH chemosensor to monitor pH changes in PBS buffer solution because of two successive protonation processes of pyridyl and imidazole moieties in acidic condition.

Cover Feature: Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence (Chem. Eur. J. 55/2017)

Cover Feature: Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence (Chem. Eur. J. 55/2017)

Aggregation-induced phosphorescence and mechanochromic luminescence of a tetraphenylethene-based gold(I) isocyanide complex

In this study, a new twisting gold(I) isocyanide complex based on tetraphenylethene (TPE), TPE-NC-Au, was designed and synthesized. It exhibits aggregation induced phosphorescence (AIP) characteristics, owing to the incorporation of Au moiety and conformation rigidification in the aggregated states. Moreover, the emission color of the crystalline solid of TPE-NC-Au changes from blue (454nm) to green (500nm) in response to mechanical grinding, due to the combined effects of conformation planarization, enhanced π⋯π stacking, as well as the emergence of aurophilic interactions in the ground amorphous state. Notably, the emission color can be restored upon solvent fuming, associating with the reconstruction of crystalline lattices. The AIP and switchable mechanochromism of TPE-NC-Au make it suitable for potential applications in bioimaging, sensing, and optoelectronic devices.

Thermostable polymeric nanomicelles of iridium(iii) complexes with aggregation-induced phosphorescence emission characteristics and their recyclable double-strand DNA monitoring.

Using 4,7-diphenyl-1,10-phenanthroline (DIP) as a main ligand and ethyl cyanoacrylate (ECA) as both an auxiliary ligand and a polymer skeleton, polymer iridium(iii) complexes (DIP)2Ir(ECA) and their nanomicelles with aggregation-induced phosphorescence emission (AIPE) activity were synthesized. The morphology, chemical structure and composition of (DIP)2Ir(ECA) nanomicelles were characterized using transmission electron microscopy, size distribution/zeta potential analysis, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Their AIPE-active effects and double-stranded DNA (dsDNA) monitoring abilities were determined using phosphorescence spectroscopy using a spectrophotofluorometer. The results showed that (DIP)2Ir(ECA) nanomicelles had a good thermostability within 0-100 °C and their size distribution was 29.14 ± 1.46 nm. These nanomicelles showed AIPE-active effects and their phosphorescence intensity increased nearly 30-fold in water compared to in acetone. These nanomicelles could be used in AIPE-active intracellular imaging and dsDNA monitoring. Owing to the specific phosphorescence quenching that occurred when dsDNA encountered (DIP)2Ir(ECA) nanomicelles, thermostable (DIP)2Ir(ECA) nanomicelles could quickly detect dsDNA with high sensitivity and could be conveniently applied not only in monitoring DNA degradation in a wider pH range (specifically in an acidic environment), but also during PCR procedures. More importantly, both (DIP)2Ir(ECA) nanomicelles and immobilized DNase I could be recycled and utilized at least four times using our novel phosphorescence "quenching-recovery" dsDNA detection procedure. The polymeric (DIP)2Ir(ECA) nanomicelles were fast, sensitive, and convenient in monitoring dsDNA and could be recycled four times owing to their thermostability, indicating their great potential in biomedical and environmental applications.

Unusual Aggregation/Gelation‐Induced Phosphorescence of Propeller‐Type Binuclear Platinum(II) Enantiomers

Three binuclear cyclometalated PtII complexes, [(ppy)Pt(µ‐SA)Pt(ppy)] (ppy = 2‐phenylpyridine, SA: salicylaldehyde azine), have been synthesized and characterized. Owing to the blockage of the intramolecular rotation of the bridging SA ligands, all three complexes exhibit propeller‐type enantiomers and aggregation‐induced phosphorescence (AIP). Interestingly, one complex with –NEt2 groups instead of long alkyl chains, amide, urea peptides, cholesterol, sugar, or steroidal groups was found to show strong phosphorescence enhancement gated by the gelation process. This unusual gelation behavior is rarely encountered, as the metallogel has no intermolecular hydrogen bonding or Pt–Pt interactions. We attribute the driving force of this gelation‐induced phosphorescence (GIP) to the propeller‐type structure, optimally balanced solubility of –NEt2 groups, enantiomer‐induced π–π stacking interactions, and strong multiple intermolecular H–C, H–O, and H–H interactions.

Bismuth‐Based Coordination Polymers with Efficient Aggregation‐Induced Phosphorescence and Reversible Mechanochromic Luminescence

AbstractTwo bismuth coordination polymers (CPs), (TBA)[BiBr4(bp4mo)] (TBA=tetrabutylammonium) and [BiBr3(bp4mo)2], which are based on the rarely used simple ditopic ligand N‐oxide‐4,4′‐bipyridine (bp4mo), show mechanochromic luminescence (MCL). High solid‐state phosphorescence quantum yields of up to 85 % were determined for (TBA)[BiBr4(bp4mo)] (λem=540 nm). Thorough investigations of the luminescence properties combined with DFT and TDDFT calculations revealed that the emission is due to aggregation‐induced phosphorescence (AIP). Upon grinding, both samples became amorphous, and their luminescence changed from yellow to orange and red, respectively. Heating or exposure to water vapor led to the recovery of the initial luminescence. These materials are the first examples of mechanochromic phosphors based on bismuth(III).

Bismuth‐Based Coordination Polymers with Efficient Aggregation‐Induced Phosphorescence and Reversible Mechanochromic Luminescence

Two bismuth coordination polymers (CPs), (TBA)[BiBr4 (bp4mo)] (TBA=tetrabutylammonium) and [BiBr3 (bp4mo)2 ], which are based on the rarely used simple ditopic ligand N-oxide-4,4'-bipyridine (bp4mo), show mechanochromic luminescence (MCL). High solid-state phosphorescence quantum yields of up to 85 % were determined for (TBA)[BiBr4 (bp4mo)] (λem =540 nm). Thorough investigations of the luminescence properties combined with DFT and TDDFT calculations revealed that the emission is due to aggregation-induced phosphorescence (AIP). Upon grinding, both samples became amorphous, and their luminescence changed from yellow to orange and red, respectively. Heating or exposure to water vapor led to the recovery of the initial luminescence. These materials are the first examples of mechanochromic phosphors based on bismuth(III).

"Aggregation induced phosphorescence" active "rollover" iridium(III) complex as a multi-stimuli-responsive luminescence material.

On reaction of 2,2'-bipyridine with iridium(iii), an "aggregation induced phosphorescence (AIP)" active "rollover" complex, [Ir(PPh3)2(bipy-H)(Cl)(H)] (bipy-H = κ(2)-N,C-2,2'-bipyridine) or [Ir(bipy-H)], is obtained. The emission colour changes from bluish-green to yellowish-orange and vice versa after repeated protonation and deprotonation of [Ir(bipy-H)], respectively, which unequivocally supports its reversible nature. [Ir(bipy-H)] is sensitive to acids with different pKa values. Tuning of the emission properties can be achieved in the presence of acids with different pKas. This behaviour allows the complex, [Ir(bipy-H)], to function as a phosphorescent acid sensor in both solution and the solid state, as well as a chemosensor for detecting acidic and basic organic vapours. The protonated form, [Ir(bipy-H)H(+)], which is generated after protonation of [Ir(bipy-H)] can be used as a solvatochromic probe for oxygen containing solvents, and also shows vapochromic properties. The emission, absorption and (1)H NMR spectra of [Ir(bipy-H)] under acidic and basic conditions demonstrate its reversible nature. DFT based calculations suggest that changes in the electron affinity of the pyridinyl rings are responsible for all these processes.

Two heteroleptic Ir(iii)–bisthienylethene compounds: syntheses, structures and aggregation-induced luminescence

Bisthienylethene hnbdtiH and its heteroleptic complexes [Ir(dfppy)2(hnbdti)]·2CH3OH (1) and [Ir(ppy)2(hnbdti)]·CH3OH (2) were synthesized and characterized by crystal structures. Aggregation-induced phosphorescence emission was observed in 1.

Aggregation-Induced Emissive Copper(I) Complexes for Living Cell Imaging

Phosphorescent binuclear copper(I) complexes [Cu2(BrphenBr)2(Ph2P(CH2)nPPh2)2](ClO4)2 with different conformations are obtained by reaction of [Cu(NCCH3)4]ClO4, 3,8-dibromo-1,10-phenanthroline (BrphenBr), and corresponding diphosphine ligands, where n = 1, 4, 5, and 6 in complexes Cu-1, Cu-2, Cu-3, and Cu-4, respectively. Complex Cu-4 exhibits both the eclipsed and the staggered conformations of 18-membered Cu2C12P4 metallacycles in a 1:1 ratio in the crystal structure. All complexes are very stable to air and moisture in the solid state because of the high level of protection of all the Cu(I) centers, N and P atom centers resulting from the close contact of BrphenBr and diphosphine ligands, and what is more important is that there exist very soft P donors and the chelating effect of aromatic N atoms. The ESI-MS result through changing the collision cell energy from 0 to 20 eV suggests that the corresponding [Cu2(Ph2P(CH2)nPPh2)2](2+) cations are the thermodynamically stable species, while [Cu2(BrphenBr)2(Ph2P(CH2)nPPh2)2](ClO4)2 are stable products in crystallization kinetics in solutions. All complexes Cu-1-Cu-4 display good aggregation-induced phosphorescence emission (AIPE) behavior in CH2Cl2/hexane mixed solvents, which are suggested to arise from restriction of intramolecular rotation. Aggregation-induced emission (AIE) of complexes Cu-1-Cu-4 in PBS/DMSO (99:1, v:v) is used for living HeLa cell imaging successfully with green intracellular emission image.

Aggregation-induced phosphorescence of iridium(iii) complexes with 2,2′-bipyridine-acylhydrazone and their highly selective recognition to Cu2+

Two cationic cyclometallated iridium(III) complexes with 2,2'-bipyridine-acylhydrazone were synthesized and characterized by spectroscopic and photophysical measurements. They exhibit remarkable aggregation-induced phosphorescent emission (AIPE) phenomenon which is caused by the restriction of rapid isomerization of the C=N bond in the acylhydrazone moiety and are supported by TD-DFT studies. They also act as a significant 'off-on' luminescent switch for Cu(2+) which works as both catalyzer and oxidant in the sensing process, resulting in hydrolysis and cyclization products which are highly emissive. The sensing properties of iridium(III) complexes are also investigated by ESI-MS spectrometry and (1)H NMR spectroscopy.