Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole “Click” Ligands

A series of cyclometalated iridium­(III) complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary ligands to give complexes with either 5- or 6-membered chelate rings were synthesized and characterized by a combination of X-ray crystallography, electron spin ionization–high-resolution mass spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy. The electronic properties of the complexes were probed using absorption and emission spectroscopy, as well as cyclic voltammetry. The relative stability of the complexes formed from each ligand class was measured, and their excited-state properties were compared. The emissive properties are, with the exception of complexes that contain a nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted pyridyl-1,2,3-triazoles using copper Cu­(I)-catalyzed azide alkyne cycloaddition, which is a commonly used “click” reaction, and this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium­(III) complexes

A Twist in Biphthalimide-Based Chromophores Enables Thermally Activated Delayed Fluorescence

Thermally activated delayed fluorescence (TADF) emitters, which convert nonemissive triplets into emissive singlets, have garnered tremendous impetus as next-generation organic electroluminescent materials. Employing donor–acceptor (D–A) designs to produce intramolecular charge transfer (ICT) states is considered an attractive strategy to effectively reduce the singlet–triplet (ΔEST) gap, thereby enhancing reverse intersystem crossing (rISC) in TADF emitters. Herein, we report two ICT chromophores (BP-1TPA and BP-2TPA) utilizing a rational design strategy based on a twisted biphthalimide acceptor core integrated with varying triphenylamine donors. We accomplish efficient TADF emission with a high photoluminescence quantum yield (PLQY) of ∼80% at ambient conditions from poly(methyl methacrylate)-doped films of these chromophores. Twisting the acceptor core ensures the separation of natural transition orbitals, leading to small ΔEST and generates an intermediate triplet excited state to facilitate rISC. The present study, therefore, sheds light on how delayed fluorescence can be realized from a simple twisted phthalimide core by rational molecular engineering and enables new insights toward exploring the aromatic imide class of molecules as potential organic light-emitting materials

Highly Fluorescent Molecularly Insulated Perylene Diimides: Effect of Concentration on Photophysical Properties

A series of four perylene diimide (PDI) chromophores were prepared with increasing steric bulk on the imide substituents with the aim of retarding the effect of concentration quenching on photoluminescence, commonly observed with these dyes. Spectroscopic investigations of the compounds in dilute solution confirmed that the photophysical properties of the PDI core chromophore were not perturbed by the bulky substituents. Solid film samples containing the PDI compounds at various concentrations dispersed in a poly­(methyl methacrylate) (PMMA) matrix were examined and compared to amorphous neat films as well as crystalline samples. The PDI compounds containing di-<i>tert</i>-butylphenyl (bPDI-3) and trityl (bPDI-4) substituents showed near unity photoluminescence quantum yield (PLQY) up to 20 mM in PMMA compared to 10% PLQY for the reference compound (bPDI-1) without molecular insulation. Surprisingly, high concentrations (>40 mM) of a phenyl-substituted PDI compound (bPDI-2) with moderate molecular insulation formed emissive aggregates that showed a higher PLQY compared to the PDI derivatives with greater steric bulk. By examining the molecular structure and solid state packing in conjunction with a series of photophysical measurements, new insights into designing highly fluorescent dyes, particularly in the solid state, were obtained. The trityl-substituted PDI compound (bPDI-4) was used in a luminescent solar concentrator with optical quantum efficiency of 54%, flux gain of 6.4, and geometric gain of 45

Photophysical Studies of Helicate and Mesocate Double-Stranded Dinuclear Ru(II) Complexes

The metal–ligand charge transfer (3MLCT) and phosphorescence-quenching metal-centered (3MC) states of the helicate and mesocate diastereoisomers of a double-stranded dinuclear polypyridylruthenium(II) complex have been investigated using ultrafast transient absorption spectroscopy. At 294 K, transient signals of the helicate decayed significantly slower than those of the mesocate, whereas at 77 K, no clear contrast in kinetics was observed. Contributions to excited-state decay from high-lying 3MLCT states were identified at both temperatures. Spectroscopic data (294 K) suggest that the 3MC state of the helicate lies above the 3MLCT and that the reverse is true for the mesocate; this was further validated by density functional theory calculations. The stabilization of the 3MC state relative to the 3MLCT state in the mesocate was explained by a reduction in ligand field strength due to distortion near the ligand bridge, which causes further deviation from octahedral geometry compared to the helicate. This work illustrates how minor structural differences can significantly influence excited state dynamics

Highly Fluorescent Molecularly Insulated Perylene Diimides: Effect of Concentration on Photophysical Properties

A series of four perylene diimide (PDI) chromophores were prepared with increasing steric bulk on the imide substituents with the aim of retarding the effect of concentration quenching on photoluminescence, commonly observed with these dyes. Spectroscopic investigations of the compounds in dilute solution confirmed that the photophysical properties of the PDI core chromophore were not perturbed by the bulky substituents. Solid film samples containing the PDI compounds at various concentrations dispersed in a poly­(methyl methacrylate) (PMMA) matrix were examined and compared to amorphous neat films as well as crystalline samples. The PDI compounds containing di-<i>tert</i>-butylphenyl (bPDI-3) and trityl (bPDI-4) substituents showed near unity photoluminescence quantum yield (PLQY) up to 20 mM in PMMA compared to 10% PLQY for the reference compound (bPDI-1) without molecular insulation. Surprisingly, high concentrations (>40 mM) of a phenyl-substituted PDI compound (bPDI-2) with moderate molecular insulation formed emissive aggregates that showed a higher PLQY compared to the PDI derivatives with greater steric bulk. By examining the molecular structure and solid state packing in conjunction with a series of photophysical measurements, new insights into designing highly fluorescent dyes, particularly in the solid state, were obtained. The trityl-substituted PDI compound (bPDI-4) was used in a luminescent solar concentrator with optical quantum efficiency of 54%, flux gain of 6.4, and geometric gain of 45

Selenium Nanoparticles as Potential Drug-Delivery Systems for the Treatment of Parkinson’s Disease

The development of efficient drug formulations for Parkinson’s disease (PD) treatment is challenged by achieving pharmacokinetic profiles, reduced side effects, and better permeability through the blood–brain barrier (BBB). As nanoparticles may facilitate the delivery of drugs in the brain due to their high-loading capacity and ability to cross biological barriers, we designed two different types of selenium nanoparticles (SeNPs) that may increase the transport of drugs across the BBB and may act as antioxidants at the site of action. The SeNPs were functionalized with polyvinylpyrrolidone (PVP) and polysorbate 20 (Tween) and characterized in terms of their size, size distribution, shape, surface charge, and colloidal stability in relevant biological media. Their drug-loading capacity was tested using dopamine and l-DOPA as therapeutically active agents for PD. Thermodynamic analysis revealed that binding processes occurred spontaneously through hydrogen bond/van der Waals interactions or electrostatic interactions. The strongest interaction was observed between PVP-SeNPs and l-DOPA or dopamine, which was characterized by a binding constant several orders of magnitude higher than for Tween-SeNPs. However, the addition of human transferrin as a model plasma protein significantly reduced this difference, which indicates the crucial role of protein corona formation in the design of drug nanodelivery systems. In vitro evaluation by cell-free and cellular transwell models showed efficient internalization of SeNP-loaded l-DOPA/dopamine by human endothelial brain cells, while facilitated BBB permeability for l-DOPA, and dopamine was achieved using PVP-SeNPs. Overall, the high potential of SeNPs as drug-delivery vehicles in PD treatment was demonstrated

Selenium Nanoparticles as Potential Drug-Delivery Systems for the Treatment of Parkinson’s Disease

The development of efficient drug formulations for Parkinson’s disease (PD) treatment is challenged by achieving pharmacokinetic profiles, reduced side effects, and better permeability through the blood–brain barrier (BBB). As nanoparticles may facilitate the delivery of drugs in the brain due to their high-loading capacity and ability to cross biological barriers, we designed two different types of selenium nanoparticles (SeNPs) that may increase the transport of drugs across the BBB and may act as antioxidants at the site of action. The SeNPs were functionalized with polyvinylpyrrolidone (PVP) and polysorbate 20 (Tween) and characterized in terms of their size, size distribution, shape, surface charge, and colloidal stability in relevant biological media. Their drug-loading capacity was tested using dopamine and l-DOPA as therapeutically active agents for PD. Thermodynamic analysis revealed that binding processes occurred spontaneously through hydrogen bond/van der Waals interactions or electrostatic interactions. The strongest interaction was observed between PVP-SeNPs and l-DOPA or dopamine, which was characterized by a binding constant several orders of magnitude higher than for Tween-SeNPs. However, the addition of human transferrin as a model plasma protein significantly reduced this difference, which indicates the crucial role of protein corona formation in the design of drug nanodelivery systems. In vitro evaluation by cell-free and cellular transwell models showed efficient internalization of SeNP-loaded l-DOPA/dopamine by human endothelial brain cells, while facilitated BBB permeability for l-DOPA, and dopamine was achieved using PVP-SeNPs. Overall, the high potential of SeNPs as drug-delivery vehicles in PD treatment was demonstrated

Selenium Nanoparticles as Potential Drug-Delivery Systems for the Treatment of Parkinson’s Disease

The development of efficient drug formulations for Parkinson’s disease (PD) treatment is challenged by achieving pharmacokinetic profiles, reduced side effects, and better permeability through the blood–brain barrier (BBB). As nanoparticles may facilitate the delivery of drugs in the brain due to their high-loading capacity and ability to cross biological barriers, we designed two different types of selenium nanoparticles (SeNPs) that may increase the transport of drugs across the BBB and may act as antioxidants at the site of action. The SeNPs were functionalized with polyvinylpyrrolidone (PVP) and polysorbate 20 (Tween) and characterized in terms of their size, size distribution, shape, surface charge, and colloidal stability in relevant biological media. Their drug-loading capacity was tested using dopamine and l-DOPA as therapeutically active agents for PD. Thermodynamic analysis revealed that binding processes occurred spontaneously through hydrogen bond/van der Waals interactions or electrostatic interactions. The strongest interaction was observed between PVP-SeNPs and l-DOPA or dopamine, which was characterized by a binding constant several orders of magnitude higher than for Tween-SeNPs. However, the addition of human transferrin as a model plasma protein significantly reduced this difference, which indicates the crucial role of protein corona formation in the design of drug nanodelivery systems. In vitro evaluation by cell-free and cellular transwell models showed efficient internalization of SeNP-loaded l-DOPA/dopamine by human endothelial brain cells, while facilitated BBB permeability for l-DOPA, and dopamine was achieved using PVP-SeNPs. Overall, the high potential of SeNPs as drug-delivery vehicles in PD treatment was demonstrated

Intracellular Distribution of Fluorescent Copper and Zinc Bis(thiosemicarbazonato) Complexes Measured with Fluorescence Lifetime Spectroscopy

The intracellular distribution of fluorescently labeled copper and zinc bis­(thiosemicarbazonato) complexes was investigated in M17 neuroblastoma cells and primary cortical neurons with a view to providing insights into the neuroprotective activity of a copper bis­(thiosemicarbazonato) complex known as Cu^II(atsm). Time-resolved fluorescence measurements allowed the identification of the Cu^II and Zn^II complexes as well as the free ligand inside the cells by virtue of the distinct fluorescence lifetime of each species. Confocal fluorescent microscopy of cells treated with the fluorescent copper­(II)­bis­(thiosemicarbazonato) complex revealed significant fluorescence associated with cytoplasmic puncta that were identified to be lysosomes in primary cortical neurons and both lipid droplets and lysosomes in M17 neuroblastoma cells. Fluorescence lifetime imaging microscopy confirmed that the fluorescence signal emanating from the lipid droplets could be attributed to the copper­(II) complex but also that some degree of loss of the metal ion led to diffuse cytosolic fluorescence that could be attributed to the metal-free ligand. The accumulation of the copper­(II) complex in lipid droplets could be relevant to the neuroprotective activity of Cu^II(atsm) in models of amyotrophic lateral sclerosis and Parkinson’s disease

Spatially Resolved Photophysical Dynamics in Perovskite Microplates Fabricated Using an Antisolvent Treatment

Perovskite microplates have important implications in the fields of functional electronics and optoelectronics. We report a facile strategy, antisolvent treatment for the growth of perovskite microplates. The morphology and crystalline quality of the microplates could be controlled by the amount of the chlorobenzene antisolvent used. An appropriate amount of antisolvent facilitates the formation of high-quality perovskite microplates with no residual precursor remaining. Spatially and temporally resolved fluorescence measurements demonstrate the heterogeneity of defect-state density and recombination processes in various perovskite microplate regions. The body center shows higher defect state density when compared with that at the edge or the corner of the microplate. Excessive antisolvent degrades the microplates into smaller particles. The results of this study reveal the factors that influence the crystallization process and photophysical dynamics of perovskite microplates