Polystyrene Immobilized Ir(III) Complex as a new Material for Optical Oxygen Sensing

Porous matrix materials in optical sensing of gaseous oxygen

The review provides comparison of porous materials that act as a matrix for luminescent oxygen indicators. These include silica-gels, sol–gel materials based on silica and organically modified silica (Ormosils), aerogels, electrospun polymeric nanofibers, metal–organic frameworks, anodized alumina, and various other microstructured sensor matrices. The influence of material structure and composition on the efficiency of oxygen quenching and dynamic response times is compared and the advantages and disadvantages of the materials are summarized to give a guide for design and practical application of sensors with desired sensitivity and response time.

Oxygen Sensing, Hypoxia Tracing and in Vivo Imaging with Functional Metalloprobes for the Early Detection of Non-communicable Diseases

Hypoxia has been identified as one of the hallmarks of tumor environments and a prognosis factor in many cancers. The development of ideal chemical probes for imaging and sensing of hypoxia remains elusive. Crucial characteristics would include a measurable response to subtle variations of pO2 in living systems and an ability to accumulate only in the areas of interest (e.g., targeting hypoxia tissues) whilst exhibiting kinetic stabilities in vitro and in vivo. A sensitive probe would comprise platforms for applications in imaging and therapy for non-communicable diseases (NCDs) relying on sensitive detection of pO2. Just a handful of probes for the in vivo imaging of hypoxia [mainly using positron emission tomography (PET)] have reached the clinical research stage. Many chemical compounds, whilst presenting promising in vitro results as oxygen-sensing probes, are facing considerable disadvantages regarding their general application in vivo. The mechanisms of action of many hypoxia tracers have not been entirely rationalized, especially in the case of metallo-probes. An insight into the hypoxia selectivity mechanisms can allow an optimization of current imaging probes candidates and this will be explored hereby. The mechanistic understanding of the modes of action of coordination compounds under oxygen concentration gradients in living cells allows an expansion of the scope of compounds toward in vivo applications which, in turn, would help translate these into clinical applications. We summarize hereby some of the recent research efforts made toward the discovery of new oxygen sensing molecules having a metal-ligand core. We discuss their applications in vitro and/or in vivo, with an appreciation of a plethora of molecular imaging techniques (mainly reliant on nuclear medicine techniques) currently applied in the detection and tracing of hypoxia in the preclinical and clinical setups. The design of imaging/sensing probe for early-stage diagnosis would longer term avoid invasive procedures providing platforms for therapy monitoring in a variety of NCDs and, particularly, in cancers.

Electrogenerated chemiluminescence from polymer-boundortho-metallated iridium(III) systems

Three ortho-metallated iridium complexes whose emission maxima fall in different regions of the electromagnetic spectrum were bound in either Nafion or poly(9-vinylcarbazole) and their electrogenerated chemiluminescence (ECL) reported. The reaction of F(Ir)pic [bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)-iridium III] with the oxidative-reductive co-reactant tri-n-propylamine (TPrA) resulted in ECL when the iridium complex was bound in Nafion. No significant ECL was observed for (btp)(2)Ir(acac) (bis[2,(2'-benzothienyl)-pyridinato-N,C3'](acetylacetonate)Ir(III)), and Ir(ppy)(3) (where ppy = 2-phenylpyridine) under these conditions. However, all three compounds displayed ECL with TPrA when bound in poly(9-vinylcarbazole).

Iridium Luminophore Complexes for Unimolecular Oxygen Sensors

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(2)(vacac), 1, Ir(ppy)(2)(vacac), 2, fac-Ir(ppy)(2)(vppy), 3, and mer-Ir(ppy)(2)(vppy), 4, where C6 = Coumarin 6, vacac = allylacetoacetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl)pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D ((1)H, (13)C) and 2-D ((1)H-(1)H, (1)H-(13)C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (tau = 6.0 micros, phi = 0.22 for 1; tau = 0.4 micros, phi = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.

High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer

To obtain the maximum luminous efficiency from an organic material, it is necessary to harness both the spin-symmetric and anti-symmetric molecular excitations (bound electron-hole pairs, or excitons) that result from electrical pumping. This is possible if the material is phosphorescent, and high efficiencies have been observed in phosphorescent organic light-emitting devices. However, phosphorescence in organic molecules is rare at room temperature. The alternative radiative process of fluorescence is more common, but it is approximately 75% less efficient, due to the requirement of spin-symmetry conservation. Here, we demonstrate that this deficiency can be overcome by using a phosphorescent sensitizer to excite a fluorescent dye. The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100%. As an example, we use this approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device.