A Sulfur-Terminal Zn(II) Complex and Its Two-Photon Microscopy Biological Imaging Application

Durable organic nonlinear optical membranes for thermotolerant lightings and in vivo bioimaging

Organic nonlinear optical materials have potential in applications such as lightings and bioimaging, but tend to have low photoluminescent quantum yields and are prone to lose the nonlinear optical activity. Herein, we demonstrate to weave large-area, flexible organic nonlinear optical membranes composed of 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate@cyclodextrin host-guest supramolecular complex. These membranes exhibited a record high photoluminescence quantum yield of 73.5%, and could continuously emit orange luminescence even being heated at 300 °C, thus enabling the fabrication of thermotolerant light-emitting diodes. The nonlinear optical property of these membranes can be well-preserved even in polar environment. The supramolecular assemblies with multiphoton absorption characteristics were used for in vivo real-time imaging of Escherichia coli at 1000 nm excitation. These findings demonstrate to achieve scalable fabrication of organic nonlinear optical materials with high photoluminescence quantum yields, and good stability against thermal stress and polar environment for high-performance, durable optoelectronic devices and humanized multiphoton bio-probes.

Field-Induced Single-Ion Magnet Behavior in Nickel(II) Complexes with Functionalized 2,2':6'-2″-Terpyridine Derivatives: Preparation and Magneto-Structural Study

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)₂](ClO₄)₂∙4H₂O (1) and [Ni(terpyepy)₂](ClO₄)₂ MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χ_MT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm^-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Paper-Strip-Based Sensors for H2S Detection: A Proof-of-Principle Study

In this work, the authors explored the interaction of a suite of fluorescent zinc complexes with H₂S. The authors provide evidence that HS⁻ binds the zinc center of all the complexes under investigation, allowing them to possibly function as sensors by a ‘coordinative-based’ approach. Naked-eye color changes occur when treating the systems with HS⁻, so the fluorescence responses are modulated by the presence of HS⁻, which has been related to a change in the energy level and coupling of excited states through a computational study. The results show the potential of the systems to function as HS⁻/H₂S colorimetric and fluorescent sensors. Paper-strip-based sensing experiments foresee the potential of using this family of complexes as chemosensors of HS⁻ in more complex biological fluids.

Recent progress in metal-based molecular probes for optical bioimaging and biosensing

Biological imaging and biosensing from subcellular/cellular level to whole body have enabled non-invasive visualisation of molecular events during various biological and pathological processes, giving great contributions to the rapid and impressive advances in chemical biology, drug discovery, disease diagnosis and prognosis. Optical imaging features a series of merits, including convenience, high resolution, good sensitivity, low cost and the absence of ionizing radiation. Among different luminescent probes, metal-based molecules offer unique promise in optical bioimaging and biosensing in vitro and in vivo, arising from their small sizes, strong luminescence, large Stokes shifts, long lifetimes, high photostability and tunable toxicity. In this review, we aim to highlight the design of metal-based molecular probes from the standpoint of synthetic chemistry in the last 2 years for optical imaging, covering d-block transition metal and lanthanide complexes and multimodal imaging agents.

The Prodigious Hydrogen Bonds with Sulfur and Selenium in Molecular Assemblies, Structural Biology, and Functional Materials

Hydrogen bonds (H-bonds) play important roles in imparting functionality to the basic molecules of life by stabilizing their structures and directing their interactions. Numerous studies have been devoted to understanding H-bonds involving highly electronegative atoms like nitrogen, oxygen, and halogens and consequences of those H-bonds in chemical reactions, catalysis, and structure and function of biomolecules; but the involvement of less electronegative atoms like sulfur and selenium in H-bond formation establishes the concept of noncanonical H-bonds. Initially belittled for the "weak" nature of their interactions, these perceptions have gradually evolved over time through dedicated efforts by several research groups. This has been facilitated by advancements in experimental methods for their detection through gas-phase laser spectroscopy and solution NMR spectroscopy, as well as through theoretical predictions from high level quantum chemical calculations.In this Account, we present insights into the versatility of the sulfur and selenium centered H-bonds (S/SeCHBs) by highlighting their multifarious applications in various fields from chemical reactions to optoelectronic properties to structural biology. Our group has highlighted the significance and strength of such H-bonds in natural and modified biomolecules. Here, we have reviewed several molecular assemblies, biomolecules, and functional materials, where the role of these H-bonds is pivotal in influencing biological functions. It is worth mentioning here that the precise experimental data obtained from gas-phase laser spectroscopy have contributed considerably to changing the existing perceptions toward S/SeCHBs. Thus, molecular beam experiments, though difficult to perform on smaller model thio- or seleno-substituted Molecules, etc. (amides, nucleobases, drug molecules), are inevitable to gather elementary knowledge and convincing concepts on S/SeCHBs that can be extended from a small four-atom sulfanyl dimer to a large 14 kDa iron-sulfur protein, ferredoxin. These H-bonds can also tailor a fascinating array of molecular frameworks and design supramolecular assemblies by inter- and intralinking of individual "molecular Lego-like" units.The discussion is indeed intriguing when it turns to the usage of S/SeCHBs in facile synthetic strategies like tuning regioselectivity in reactions, as well as invoking phenomena like dual phosphorescence and chemiluminescence. This is in addition to our investigations of the dispersive nature of the hydrogen bond between metal hydrides and sulfur or selenium as acceptor, which we anticipate would lead to progress in the areas of proton and hydride transfer, as well as force-field design. This Account demonstrates how ease of fabrication, enhanced efficiency, and alteration of physicochemical properties of several functional materials is facilitated owing to the presence of S/SeCHBs. Our efforts have been instrumental in the evaluation of various S/SeCHBs in flue gas capture, as well as design of organic energy harvesting materials, where dipole moment and polarizability have important roles to play. We hope this Account invokes newer perspectives with regard to how H-bonds with sulfur and selenium can be adequately adopted for crystal engineering, for more photo- and biophysical studies with different spectroscopic methods, and for developing next-generation field-effect transistors, batteries, superconductors, and organic thin-film transistors, among many other multifunctional materials for the future.

A novel water-soluble quinoline–indole derivative as a three-photon fluorescent probe for identifying nucleolus RNA and mitochondrial DNA

We present the design and synthesis of water-soluble quinoline–indole-based derivatives (IM-1, IM-2, and IM-3) with three-photon absorption activity.

ZnII Complexes for Bioimaging and Correlated Applications

Zinc is a biocompatible element that exists as the second most abundant transition metal ion and an indispensable trace element in the human body. Compared to traditional metal-organic complexes systems, d¹⁰ metal Zn^II complexes not only exhibit a large Stokes shift and good photon stability but also possess strong emission and low cytotoxicity with a relatively small molecular weight. The use of Zn^II complexes has emerged in the last decade as a versatile and convenient tool for numerous biological applications, including bioimaging, molecular and protein recognition, as well as photodynamic therapy. Herein, we review recent developments involving Zn^II metal complexes applied as specific subcellular compartment imaging probes and their correlated utilizations.

A Series of Zn(II) Terpyridine-Based Nitrate Complexes as Two-Photon Fluorescent Probe for Identifying Apoptotic and Living Cells via Subcellular Immigration

Two-photon active probe to label apoptotic cells plays a significant role in biological systems. However, discrimination of live/apoptotic cells at subcellular level under microscopy remains unachieved. Here, three novel Zn(II) terpyridine-based nitrate complexes (C1-C3) containing different pull/push units were designed. The structures of the ligands and their corresponding Zn(II) complexes were confirmed by single-crystal X-ray diffraction analysis. On the basis of the comprehensive comparison, C3 had a suitable two-photon absorption cross section in the near-infrared wavelength and good biocompatibility. Under two-photon confocal microscopy and transmission electron microscopy, it is found that C3 could target mitochondria in living cells but immigrate into the nucleolus during the apoptotic process. This dual-functional probe (C3) not only offers a valuable image tool but also acts as an indicator for cell mortality at subcellular level in a real-time manner.

A luminescent aluminium salen complex allows for monitoring dynamic vesicle trafficking from the Golgi apparatus to lysosomes in living cells

Tracking vesicle transport from the Golgi apparatus to lysosomes based on an Al³⁺–phospholipid coordination strategy.

The Golgi apparatus is well-known as the center of vesicle trafficking whose malfunction might cause the breakdown of overall cellular architecture and ultimately cell death. The development of fluorescent probes to not only precisely stain the Golgi apparatus but also monitor dynamic vesicle trafficking is of great significance. While fluorescent proteins and fluorescent lipid analogs have been reported, they are sometime limited by either overexpression and toxicity or lack of high selectivity, respectively. We herein report a novel approach based on metal-induced coordination between the phosphate anions of phospholipids and the metal center of a luminescent Alsalen complex AlL, which can in situ track membrane vesicle trafficking from the Golgi apparatus to the lysosomes in living cells. This work opens a new avenue for designing luminescent metal probes based on the Lewis acidity of metal ions and allows the use of metal ions with different charge states, polarities, and reactivities within a similar structural scaffold to expand coordination chemistry for biological studies.

Coordination coupling enhanced two-photon absorption of a ZnS-based microhybrid for two-photon microscopy imaging in HepG2

Coordination coupling induced self-assembly of ZnS microparticles was performed with the help of a π-conjugated sulphur-terminal Zn(ii) complex ZnS₂L (L = N-hexyl-3-{2-[4-2,2':6',2''-terpyridin-4'-yl-phenyl]ethenyl}-carbazole). The interactions between ZnS and ZnS₂L components at the interface, which were analyzed by far-IR and XPS, resulted in a tunable single-photon excited fluorescence and an enhanced nonlinear optical response, including a two-photon absorption cross section and a two-photon excited fluorescence. Such an enhancement in nonlinear optical properties was triggered by the coordination coupling effect between terminal S atoms of ZnS₂L and naked Zn²⁺ ions at the surface of ZnS particles. Thus, the novel hybrid system displayed a unique two-photon excited fluorescence to facilitate promising two-photon microscopy imaging of HepG2 cells upon NIR light illumination at 840 nm. The hybrid shows a stronger ability to enter the cells than free ZnS₂L.

Lighting the Way to See Inside Two-Photon Absorption Materials: Structure-Property Relationship and Biological Imaging

The application of two-photon absorption (2PA) materials is a classical research field and has recently attracted increasing interest. It has generated a demand for new dyes with high 2PA cross-sections. In this short review, we briefly cover the structure-2PA property relationships of organic fluorophores, organic-inorganic nanohybrids and metal complexes explored by our group. (1) The two-photon absorption cross-section (δ) of organic fluorophores increases with the extent of charge transfer, which is important to optimize the core, donor-acceptor pair, and conjugation-bridge to obtain a large δ value. Among the various cores, triphenylamine appears to be an efficient core. Lengthening of the conjugation with styryl groups in the D-π-D quadrupoles and D-π-A dipoles increased δ over a long wavelength range than when vinylene groups were used. Large values of δ were observed for extended conjugation length and moderate donor-acceptors in the near-IR wavelengths. The δ value of the three-arm octupole is larger than that of the individual arm, if the core has electron accepting groups that allow significant electronic coupling between the arms; (2) Optical functional organic/inorganic hybrid materials usually show high thermal stability and excellent optical activity; therefore the design of functional organic molecules to build functional organic-inorganic hybrids and optimize the 2PA properties are significant. Advances have been made in the design of organic-inorganic nanohybrid materials of different sizes and shapes for 2PA property, which provide useful examples to illustrate the new features of the 2PA response in comparison to the more thoroughly investigated donor-acceptor based organic compounds and inorganic components; (3) Metal complexes are of particular interest for the design of new materials with large 2PA ability. They offer a wide range of metals with different ligands, which can give rise to tunable electronic and 2PA properties. The metal ions, including transition metals and lanthanides, can serve as an important part of the structure to control the intramolecular charge-transfer process that drives the 2PA process. As templates, transition metal ions can assemble simple to more sophisticated ligands in a variety of multipolar arrangements resulting in interesting and tailorable electronic and optical properties, depending on the nature of the metal center and the energetics of the metal-ligand interactions, such as intraligand charge-transfer (ILCT) and metal-ligand charge-transfer (MLCT) processes. Lanthanide complexes are attractive for a number of reasons: (i) their visible emissions are quite long-lived; (ii) their absorption and emission can be tuned with the aid of appropriate photoactive ligands; (iii) the accessible energy-transfer path between the photo-active ligands and the lanthanide ion can facilitate efficient lanthanide-based 2PA properties. Thus, the above materials with excellent 2PA properties should be applied in two-photon applications, especially two-photon fluorescence microscopy (TPFM) and related emission-based applications. Furthermore, the progress of research into the use of those new 2PA materials with moderate 2PA cross section in the near-infrared region, good Materials 2017, 10, 223 2 of 37 biocompatibility, and enhanced two-photon excited fluorescence for two-photon bio-imaging is summarized. In addition, several possible future directions in this field are also discussed (146 references).

Probe for simultaneous membrane and nucleus labeling in living cells and in vivo bioimaging using a two-photon absorption water-soluble Zn(ii) terpyridine complex with a reduced π-conjugation system

Small, biocompatible and water-soluble molecules with high two-photon absorption (2PA) cross-section values (δ) are in high demand for specific bioimaging applications. Here, two novel terpyridine derivative ligands with donor-acceptor (D-A) (L1) and donor-π-acceptor (D-π-A) (L2) models, and their corresponding Zn(ii) complexes are designed and characterized. It was found that the two-photon absorption cross section values (δ) in the near-infrared region (NIR, about 800 nm) are significantly enhanced for complexes 1 and 2 compared to their free D-A type ligand L1, while those of complexes 3 and 4 were greatly decreased relative to their free ligand L2, thus confirming that the smaller ligand (D-A type) displays a suitable Turn-ON fluorescence pair for two-photon fluorescence microscopy (2PFM). Firstly, the potential of simultaneously labeling a live cell plasma membrane and nucleus using complex 1 is demonstrated. In addition, live larval and adult zebrafish incubated with an optimal concentration of 1 demonstrated clear brain uptake. Lastly and importantly, using such a probe to visualize the blood-brain-barrier (BBB) capillary endothelial cells and penetrate the BBB into the central nervous system (CNS) intravenously in a mouse model is also explored.

Recent Advances in the Synthesis, Characterization and Application of Zn+-containing Heterogeneous Catalysts

Monovalent Zn+ (3d104s1) systems possess a special electronic structure that can be exploited in heterogeneous catalysis and photocatalysis, though it remains challenge to synthesize Zn+-containing materials. By careful design, Zn+-related species can be synthesized in zeolite and layered double hydroxide systems, which in turn exhibit excellent catalytic potential in methane, CO and CO2 activation. Furthermore, by utilizing advanced characterization tools, including electron spin resonance, X-ray absorption fine structure and density functional theory calculations, the formation mechanism of the Zn+ species and their structure-performance relationships can be understood. Such advanced characterization tools guide the rational design of high-performance Zn+-containing catalysts for efficient energy conversion.

Study of the one-photon and two-photon properties of two water-soluble terpyridines and their zinc complexes

Two water soluble 2,2':6',2''-terpyridine derivatives (TPYOH and O3TPY) with a di(hydroxyethyl)amino or a long (2-(2-methoxyethoxy)ethoxy)benzyl group, respectively, were designed and synthesized. The two terpyridine ligands and their Zn(ii) complexes display strong one-photon fluorescence. An unusually large solvatochromism effect in ethanol and water was found, which was ascribed to their interactions with the solvent through hydrogen bonds. All the four compounds show evident two-photon absorption ability when evaluated by Z-scan technology. The free ligands could give distinct two-photon excited fluorescence, and the emission of O3TPY responded linearly with Zn(2+) under the excitation of a 780 nm femtosecond laser. Only the complex ZnO3TPY, which possesses a large π conjugation system and suitable election-donating groups, displayed emission maxima at 595 nm when excited by a 680-880 nm laser.

A photoactivatable Znsalen complex for super-resolution imaging of mitochondria in living cells

We report the first transition metal complex, Znsalen J-S-Alk, as a photoactivatable probe for super-resolution imaging of mitochondria.

Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

Four novel Zn(II) terpyridine complexes (ZnLCl2, ZnLBr2, ZnLI2, ZnL(SCN)2) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limiting (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations (TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence (OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080 nm. These results revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior optical power limiting property.

Synthesis, crystal structures and two-photon absorption properties of triphenylamine cyanoacetic acid derivative and its organooxotin complexes

Three novel organooxotin complexes (Z1, Z2 and Z3) exhibit large 2PA cross-section per molecular weight and can be used as potential anti-tumor agents.

Mechanism and application of halogen bond induced fluorescence enhancement and iodine molecule cleavage in solution

Halogen bonding between iodine and ciprofloxacin (I⋯N XB) induces I–I cleavage with fluorescence enhancement.

Crystal structure of di-chlorido-(2,2':6',2''-terpyridine-κ(3) N,N',N'')zinc: a redeter-min-ation

The crystal structure of the title compound, [ZnCl₂(C₁₅H₁₁N₃)], was redetermined based on modern CCD data. In comparison with the previous determination from photographic film data [Corbridge & Cox (1956 ▶). J. Chem. Soc.159, 594–603; Einstein & Penfold (1966 ▶). Acta Cryst.20, 924–926], all non-H atoms were refined with anisotropic displacement parameters, leading to a much higher precision in terms of bond lengths and angles [e.g. Zn—Cl = 2.2684 (8) and 2.2883 (11) compared to 2.25 (1) and 2.27 (1) Å]. In the title mol­ecule, the Zn^II atom is five-coordinated in a distorted square-pyramidal mode by two Cl atoms and by the three N atoms from the 2,2′:6′,2′′-terpyridine ligand. The latter is not planar and shows dihedral angles between the least-squares planes of the central pyridine ring and the terminal rings of 3.18 (8) and 6.36 (9)°. The mol­ecules in the crystal structure pack with π–π inter­actions [centroid–centroid distance = 3.655 (2) Å] between pyridine rings of neighbouring terpyridine moieties. These, together with inter­molecular C—H⋯Cl inter­actions, stablize the three-dimensional structure.

Single-layered graphitic-C(3)N(4) quantum dots for two-photon fluorescence imaging of cellular nucleus

A promising, safe, and economic fluorescent probe, g-C3 N4 single-layered QDs, is introduced for two-photon fluorescence imaging of the cellular nucleus for the first time. The large two-photon absorption cross section, the high photostability, good biocompatibility and non-toxicity, negligible photothermal effect, and specific interaction with DNA render the single-layered g-C3 N4 QDs as a promising candidate for in vivo and in vitro two-photon fluorescence imaging and further biomedical applications.

Fluorescent styryl dyes based on novel 4-methoxy-9-methyi-9H-carbazole-3-carbaldehyde--synthesis, photophysical properties and DFT computations

Novel carbazole based styryl derivatives (6a-6c) having styryl group at third position and a methoxy substitution were synthesized by condensing 4-methoxy-9-methyl-9H-carbazole-3-carbaldehyde 3 and different active methylene derivatives (5a-5c). Evaluated photophysical properties of these synthesized novel chromophores, studied the effect of solvent polarity on absorption, emission and quantum yield of these styryl derivatives. DFT and TD-DFT computations are carried out to study structural, molecular, electronic and photophysical parameters of dyes. The ratio of ground state to excited state dipole moment was calculated using Bakhshiev and Kawski-Chamma-Viallet correlations.

Rational design of phosphorescent chemodosimeter for reaction-based one- and two-photon and time-resolved luminescent imaging of biothiols in living cells

A selective phosphorescent biothiols probe is synthesized based on Ir(III) complex 1, which has 2,2'-biquinoline as the N^N ligand for realizing the satisfied two-photon absorption cross-section and two-functionalized 2-phenylpyridine ligands with an α,β-unsaturated ketone moiety as the thiol reaction site. The one- and two-photon optical properties of 1 are investigated through UV-vis absorption spectrum and photoluminescence spectrum. This Ir(III) complex can act as an excellent one- and two-photon excited "OFF-ON" phosphorescent probe for biothiols based on the 1,4-addition of biothiol to α,β-unsaturated ketones. Moreover, one- and two-photon-induced luminescent imagings of biothiols in living cells are also realized. Furthermore, the experiments of time-resolved photoluminescence technique and fluorescence lifetime imaging microscopy demonstrate that 1 is able to detect biothiols in the presence of strong background fluorescence. In addition, probe 1 is adsorbed into the shell of mesoporous silica nanoparticles with core-shell structure to form a nanoprobe, which can realize the ratiometric detection of biothiols in absolute water solution and living cells based on two phosphorescent signals.

A white-light-emitting LnMOF with color properties improved via Eu3+ doping: an alternative approach to a rational design for solid-state lighting

The intrinsic white-light-emitting properties of a lanthanide metal-organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu(3+) into the host framework by virtue of the isostructural character of the La(3+) and Eu(3+) compounds and efficient sensitization of ligands toward Eu(3+) ions.

{9-Hexyl-2-[2-phenyl-6-(pyridin-2-yl)pyridin-4-yl]-9H-carbazole}diiodidozinc

In the title compound, [ZnI₂(C₃₄H₃₁N₃)], the Zn^II atom is four-coordinated by two I atoms and the pyridine N atoms from the bidentate 6′-phenyl-2,2′-bi­pyridine ligand in a distorted tetra­hedral geometry.

Design and synthesis of a luminescent cyclometalated iridium(III) complex having N,N-diethylamino group that stains acidic intracellular organelles and induces cell death by photoirradiation

Cyclometalated iridium(III) complexes have received considerable attention and are important candidates for use as luminescent probes for cellular imaging because of their potential photophysical properties. We previously reported that fac-Ir(atpy)(3)4 (atpy = 2-(5'-amino-4'-tolyl)pyridine) containing three amino groups at the 5'-position of the atpy ligand shows a maximum red emission (at around 600 nm) under neutral and basic conditions and a green emission (at 531 nm) at acidic pH (pH 3-4). In this Article, we report on the design and synthesis of a new pH-sensitive cyclometalated Ir(III) complex containing a 2-(5'-N,N-diethylamino-4'-tolyl)pyridine (deatpy) ligand, fac-Ir(deatpy)(3)5. The complex exhibits a considerable change in emission intensity between neutral and slightly acidic pH (pH 6.5-7.4). Luminescence microscopic studies using HeLa-S3 cells indicate that 5 can be used to selectively stain lysosome, an acidic organelle in cells. Moreover, complex 5 is capable of generating singlet oxygen in a pH-dependent manner and inducing the death of HeLa-S3 cells upon photoirradiation at 377 or 470 nm.

Synthesis of benzobisoxazole-based D-π-A-π-D organic chromophores with variable optical and electronic properties

A series of symmetrical D-π-A-π-D molecules comprised of benzo[1,2-d;4,5-d']bisoxazole (BBO) and various arylenevinylenes was synthesized via a Knoevenagel condensation of 2,6-dimethyl BBO and the corresponding aryl aldehydes. The resulting compounds had energy levels that were easily modulated and broad absorptions in the visible spectrum. They also demonstrated high fluorescence quantum yields in solution. The solvatochromism of several derivatives was examined in a number of solvents, and it was found that the emission of the triphenylamine derivative varied by almost 100 nm, depending on the polarity of the solvent. Collectively, these results indicate that the optical and electronic properties of benzobisoxazoles are readily tuned through the choice of aryl co-monomer.