A self-calibrating bipartite viscosity sensor 1 for cellular mitochondria, composed of coumarin and boron-dipyrromethene (BODIPY) with a rigid phenyl spacer and a mitochondria-targeting unit, was synthesized. The sensor showed a direct linear relationship between the fluorescence intensity ratio of BODIPY to coumarin or the fluorescence lifetime ratio and the media viscosity, which allowed us to determine the average mitochondrial viscosity in living HeLa cells as ca. 62 cP (cp). Upon treatment with an ionophore, monensin, or nystatin, the mitochondrial viscosity was observed to increase to ca. 110 cP.

A new phosphorescent zinc sensor (ZIrF) was constructed based on an Ir(III) complex bearing two 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands and a neutral 1,10-phenanthroline (phen) ligand. A zinc-specific di(2-picolyl)amino (DPA) receptor was introduced at the 4-position of the phen ligand via a methylene linker. The cationic Ir(III) complex exhibited dual phosphorescence bands in CH3CN solutions originating from blue and yellow emission of the dfppy and phen ligands, respectively. Zinc coordination selectively enhanced the latter, affording a phosphorescence ratiometric response. Electrochemical techniques, quantum chemical calculations, and steady-state and femtosecond spectroscopy were employed to establish a photophysical mechanism for this phosphorescence response. The studies revealed that zinc coordination perturbs nonemissive processes of photoinduced electron transfer (PeT) and intraligand charge transfer (ILCT) transition occurring between DPA and phen. ZIrF can detect zinc ions in a reversible and selective manner in buffered solution (pH 7.0, 25 mM PIPES) with Kd = 11 nM and pKa = 4.16. Enhanced signal-to-noise ratios were achieved by time-gated acquisition of long-lived phosphorescence signals. The sensor was applied to image biological free zinc ions in live A549 cells by confocal laser scanning microscopy. A fluorescence lifetime imaging microscope (FLIM) detected an increase in photoluminescence lifetime for zinc-treated A549 cells as compared to controls. ZIrF is the first successful phosphorescent sensor that detects zinc ions in biological samples.

Polymeric organic photovoltaic (OPV) cells are promising candidates for low-cost, high-performance energy sources due to their low material and processing costs, flexibility, and ease of manufacturing by solution processes. However, low power-conversion efficiency (PCE) has impeded the development of OPV cells. The low PCE in OPV solar cells has been attributed to low carrier mobility, which is related to the transport length of the charge carriers within active layers. Graphene can be an ideal material for assisting the charge transport in the active layer of OPV cells due to its excellent charger carrier mobility, thermal and chemical stability, and compatibility with the solution process. In this work, we demonstrated for the first time an improvement of the PCE (up to 40%) in OPV bulk-heterojunction (BHJ) cells by incorporating charge-selective graphene flakes into the BHJ active layer. The charge selectivity of graphene flakes was achieved by nitrogen doping (N-doped graphene). The N-doped graphene, when mixed in the active layer (N-doped graphene/polymer:fullerene composites), provided transport pathways exclusively to specific charge carriers through the modulation of band-gap structures. We discuss further the enhancement of the PCE in OPV cells with respect to charge-carrier mobility. Broader contextOrganic solar cells have received a lot of attention due to their low production costs, easy scalability to large-areas and applicability on exible substrates. One of the main challenges to widespread application in practical devices is their low power conversion efficiency (PCE). This is largely because of the low charge-carrier mobilities and poor charge transfer characteristics in organic materials, resulting in short carrier lifetimes and reduced charge collection efficiencies. In this work, we demonstrate that the use of nitrogen-doped graphene improves the power conversion efficiency of a bulk-heterojunction solar cell system. The nitrogen-doped graphene provides transport pathways to specic charge carriers through the modulation of band structures when mixed into the active layer. We believe that the added functionality of charge selectivity in conductive graphene akes gives a new design parameter for increasing the PCE of bulk-heterojunction solar cells.

Porous gold nanofibers of different diameters from 43 to 219 nm were fabricated using electrochemical deposition techniques. Gold-silver alloy were electrochemically deposited in the form of nanofibers within the porous alumina templates of various diameters and only a silver phase was chemically removed using nitric acid. Field-emission scanning electron microscope images of the resulting nanofibers show a high-quality nanoporous network with homogeneous pores. A notable surface-enhanced Raman scattering (SERS) has been observed for all porous gold nanofibers of which scattering efficiencies are distinctly higher than that of the smooth solid gold nanofibers without porosity. As the diameter of porous gold nanofibers decreases, the observed SERS efficiency gradually increases. Controlled fabrication of lateral width of gold nanofibers reveals promising application for high efficient and stable molecular sensing platforms.

Despite the promising photofunctionalities, phosphorescent probes have been examined only to a limited extent, and the molecular features that provide convenient handles for controlling the phosphorescence response have yet to be identified. We synthesized a series of phosphorescence zinc sensors based on a cyclometalated heteroleptic Ir(III) complex. The sensor construct includes two anionic cyclometalating ligands and a neutral diimine ligand that tethers a di(2-picolyl)amine (DPA) zinc receptor. A series of cyclometalating ligands with a range of electron densities and band gap energies were used to create phosphorescence sensors. The sensor series was characterized by variable-temperature steady-state and transient photoluminescence spectroscopy studies, electrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. The studies demonstrated that the suppression of nonradiative photoinduced electron transfer (PeT) from DPA to the photoexcited Ir(IV) species provided the underlying mechanism that governed the phosphorescent response to zinc ions. Importantly, the Coulombic barrier, which was located on either the cyclometalating ligand or the diimine ligand, negligibly influenced the PeT process. Phosphorescence modulation by PeT strictly obeyed the Rehm-Weller principle, and the process occurred in the Marcus-normal region. These findings provide important guidelines for improving sensing performance; an efficient phosphorescence sensor should include a cyclometalating ligand with a wide band gap energy and a deep oxidation potential. Finally, the actions of the sensor were demonstrated by visualizing the intracellular zinc ion distribution in HeLa cells using a confocal laser scanning microscope and a photoluminescence lifetime imaging microscope.

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures.

Multicolor or white light-emitting systems have attracted great attention because of their potential uses as lighting sources and full-color displays. [ 1 ] In recent years, numerous efforts have been devoted to the development of low-cost, simple processes for the fabrication of pure white-light sources as an alternative for conventional lighting sources. [2][3][4] Fluorescent quantum dots (QDs) have been explored as one of the promising candidate materials due to their pure color emission spectra, high fl uorescence quantum yield, and photochemical stability. [ 5 , 6 ] However, the emission spectrum produced by each individual QD is narrow, thus requiring simultaneous emission from more than two colored QDs to illuminate across the visible regime. Typically, this is achieved through a combination of either three different QDs emitting red, green and blue light or two different ones emitting orange/red and green/blue light. In such a system, undesired Förster resonance energy transfer (FRET) between QDs often occurs, decreasing the effi ciency of the white light emission. [ 7 , 8 ] The controlled spatial isolation of multiple QDs is made necessary by the strong dependence of the energy-transfer process on the donor-acceptor distance on the nanometer scale. [ 9 , 10 ] One promising method to organize multiple fl uorescent QDs into specifi c sites is to use block copolymers (BCPs).Self-assembled BCPs can yield various nanostructures when the volume fraction and molecular weight of the blocks are controlled, providing a means to template various nanoscale objects with controlled positions. [11][12][13][14][15][16][17][18][19] Controlling the position of the nanoparticles within the BCP template typically requires careful modifi cation of the nanoparticle surfaces to induce enthalpic interactions between the particle surfaces and the BCP domains. [ 13 , 20-26 ] Specifi cally, the confi nement of nanoparticles within BCP spheres or cylinders requires very specifi c and strong interactions between the particle surfaces and the BCP chains. However, modifi cation of QD surfaces in this way can reduce their effectiveness for the intended purpose because their fl uorescent quantum yields decrease during the process of exchanging ligands on their surfaces. [ 27 ] One promising approach is to use small molecule linkers that can interact favorably with both the BCP chains and the ligands on the QD surface. [ 28 , 29 ] This leads to the ability to selectively place nanoparticles in one BCP template domain without any further modifi cation of the surfaces. Although the ability of self-assembled BCP structures to control FRET between differentcolored fl uorophores consisting of either (1) two different dyes or (2) a dye and a QD has previously been assessed, the use of such structures has never been explored for systems consisting of only QDs, to the best of our knowledge. [ 4 , 30 , 31 ] Furthermore, these systems have never before involved the confi nement of QDs in the minor block domains of the BCPs (i.e., spheres an...

We herein report a fluorescent bimodal probe (1) capable of determining ER viscosity and polarity changes using FLIM and fluorescence ratiometry, respectively; during ER stress caused by tunicamycin, the viscosity was increased from ca. 129.5 to 182.0 cP and the polarity of the ER (dielectric constant, ε) enhanced from 18.5 to 21.1.