C60(CF3)2 stabilizes OPV donors toward photodegradation.

The photobleaching dynamics of a series of three organic photovoltaic (OPV) donor polymer blends with five different fullerenes are presented. The fullerenes studied include PC60BM and four perfluoroalkylfullerenes with relatively large electron affinities, namely C60(CF3)2, C60(i-C3F7)2, C60(CF3)4, and C60(CF3)8. The donor polymers were all based on cyclopentadithiophene (CPDT) and thienopyrrolodione (TPD), but the TPD side chains were designed to include alkyl, partially fluorinated alkyl, and fluorinated phenyl groups to improve miscibility of the active layer components. Exciton harvesting was probed with photoluminescence quenching measurements. Accelerated photodegradation studies of polymer:fullerene blends were then carried out under white light illumination at ∼1.2 suns in air. A strong correlation was observed between the polymer donor photobleaching rate and the electron affinity of the fullerene. The most dramatic effect was observed for a blend of C60(CF3)8 with the donor containing fluorinated phenyl groups: the blend required 150 times the dosing of photons to bleach to 80% of its initial optical density than an analagous blend of PC60BM and non-fluorinated donor polymer. These results ultimately suggest that appropriate fluorination strategies applied to both the donor and acceptor can be a viable route toward a new paradigm of intrinsically photo- and phase-stable OPV active layers.

Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(100) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(100) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 Wm(-2)) illumination resulting from the covalently bound surface dipole. Though Xray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(100) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm(-2) within -0.5 V of the reversible hydrogen electrode.

Due to the inherent challenges in probing nanoscale properties within bulk heterojunction (BHJ) active layers of organic photovoltaic (OPV) devices, the relationship between morphology and nanoscale electronic structure is not well understood. Here, we employ scanning tunneling microscopy (STM) dI/dV imaging and localized density of states (DOS) spectra to investigate the influence of additives on morphology in a high-performance OPV system. In short, we are able to correlate the use of diiodooctane (DIO) additive with significant changes to the distribution of the localized DOS, most notably a broader distribution of PCEIO polymer HOMO levels and PC7QBM fullerene LIJMO levels, as well as significantly smaller domain sizes and significantly higher overall device efficiencies. We further correlate this data with a nearly 3-fold increase in charge carrier lifetimes in the active layer when DIO is employed, determined by time-resolved microwave conductivity (TRMC) measurements. The results are consistent with the growing body of literature evidence that DIO promotes the formation of a polymer/fullerene mixed phase and therefore highlight the unique information that this combination of techniques can provide when investigating OPV active layer morphology.

Over the last few years, considerable efforts are taken, in order to find a molecular fluorescent probe fulfilling their applicability requirements. Due to a good optical properties and affinity to biological structures conjugated oligoelectrolytes (COEs) can be considered as a promising dyes for application in fluorescence-based bioimaging. In this work, we synthetized COEs with phenylenevinylene core (PV-COEs) and applied as fluorescent membranous-specific probes. Cytotoxicity effects of each COE were probed on cancerous and non-cancerous cell types and little to no toxicity effects were observed at the high range of concentrations. The intensity of cell fluorescence following the COE staining was determined by the photoluminescence analysis and fluorescence activated cell sorting method (FACS). Intercalation of tested COEs into mammalian cell membranes was revealed by fluorescent and confocal microscopy colocalization with commercial dyes specific for cellular structures including mitochondria, Golgi apparatus and endoplasmic reticulum. The phenylenevinylene conjugated oligoelectrolytes have been found to be suitable for fluorescent bioimaging of mammalian cells and membrane-rich organelles. Due to their water solubility coupled with spontaneous intercalation into cells, favorable photophysical features, ease of cell staining, low cytotoxicity and selectivity for membranous structures, PV-COEs can be applied as markers for fluorescence imaging of a variety of cell types.

This work investigates the influence of fluorination of both donor and acceptor materials on the generation of free charge carriers in small molecule donor/fullerene acceptor BHJ OPV active layers. A fluorinated and non-fluorinated small molecule analogue were synthesized and their optoelectronic properties characterized. The intrinsic photoconductance of blends of these small molecule donors was investigated using time-resolved microwave conductivity. Blends of the two donor molecules with a traditional non-fluorinated fullerene (PC 70 BM) as well as a fluorinated fullerene (C 60 (CF 3 )2-1) were investigated using 5% and 50% fullerene loading. We demonstrate for the first time that photoconductance in a 50:50 donor:acceptor BHJ blend using a fluorinated fullerene can actually be improved relative to a traditional non-fluorinated fullerene by fluorinating the donor molecule as well.

The interaction of the water-soluble conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) (degree of polymerization, DP, ∼3-6) with various concentrations of a homologous series of oppositely charged amphiphilic phenylenevinylene oligomers was investigated in water:dioxane mixtures and in aqueous micellar solutions of the non-ionic surfactant n-dodecylpentaoxyethylene glycol ether. The excellent spectral overlap between the CPE fluorescence and the conjugated oligoelectrolyte (COE) absorption indicates that energy transfer between these is a highly favored process, and can be tuned by changing the COE chain length. This is supported by time-resolved fluorescence data. The overall results provide support for different types of self-assembly, which are sensitive to the solvent environment and to the size of the phenylenevinylene oligoelectrolyte chain. It is suggested that large aggregates are formed in water:dioxane mixtures, while decorated core-shell structures are present in the surfactant solutions.

Conjugated phenylenevinylene oligoelectrolytes, which consist of a phenylenevinylene core equipped at each end with hydrophilic pendent groups, are shown to be good candidates for mammalian cell membrane staining. When used in the micromolar concentration range, they express low to moderate cell toxicity for selected regular and cancerous cell lines as tested for adherent and suspension cells.

A homologous series of p-phenylenevinylene oligomers (PPV) (n = 3-5) with terminal dialkylamino groups have been synthesized, and characterized. The photophysical and solvatochromic properties of oligomers with three, four, and five phenyl groups were investigated in solution through steady-state and time-resolved fluorescence. The red-shift seen in absorption and photoluminescence (PL) spectra on increasing chain length is consistent with an extension of the conjugation length. Decreasing solvent polarity leads to small shifts of the absorption spectra and large blue-shifts of the PL spectra. Time-resolved emission on these oligomers allows separation of conformational and solvent contributions to their photophysical behavior. Global analysis of fluorescence decays collected at different emission wavelengths shows biexponential behavior in toluene at room temperature. The longer time appears as a decay component at all emission wavelengths and decreases from 949 to 850 ps with increasing chain length. The shorter time component (19-26 ps) appears as a decay at the onset of the emission spectrum and as a rise time at longer wavelengths. With PPV oligomers substituted on the phenyl rings, similar kinetic characteristics have been attributed to conformational relaxation of the initially excited oligomer into a more planar conjugation. However, the solvent and temperature dependence exclude this hypothesis. Instead, this component is assigned to specific interaction between the oligomer main chain and the solvent. Information on backbone conformational behavior has been obtained by temperature dependence of multinuclear NMR studies coupled with molecular dynamics simulations, Moller-Plesset 2, and density functional theory (DFT) calculations. The major result is that conformational relaxation in the excited state can be decoupled from solvent relaxation. Since conformational relaxation enhances nonradiative decay, control of this is expected to improve photoluminescence yields in these systems.

An amphiphilic conjugated oligoelectrolyte (COE) that spontaneously intercalates into lipid membranes enables Shewanella oneidensis to use a graphite electrode as the sole electron donor for succinate production. Current consumed in a poised electrochemical system by Shewanella with micromolar concentrations of COE correlates well with the succinate produced via fumarate reduction as determined by HPLC analysis. Confocal microscopy confirms incorporation of the COE into the microbes on the electrode surface. This work presents a unique strategy to induce favorable bioelectronic interactions for the production of reduced microbial metabolites.

A series of conjugated oligoelectrolytes with structural variations is used to stain E. coli. By taking advantage of a high-throughput screening platform that incorporates gold anodes, it is found that MFCs with COE-modified E. coli generate significantly higher power densities, relative to unmodified E. coli. These findings highlight the potential of using water-soluble molecules inspired by the work on organic semiconductors to improve electrode/microbe interfaces.

In the presented study, a new application for distyrylbenzene oligoelectrolyte, named DSBN+, as a marker for bioimaging is presented. DSBN+ is a water-soluble, conjugated oligoelectrolyte (COE) with novel photophysical and solvatochromatic properties. Previous studies have shown that this compound spontaneously inserts into bilayer membranes in both synthetic and microbial living systems and can facilitate visualization of cell membranes through fluorescence imaging. In the presented research, we seek to further study and exploit the multifunctional nature of DSBN+ in terms of membrane interactions and photophysical properties for visualization of membranous structures of more complex mammalian cells, namely a human cervical carcinoma (HeLa) cell line. Obtained results confirm the possibility of applying DSBN+ as a fluorescent dye for bioimaging of membranes in human cell cultures systems, both in live-cell imaging and in the studies required formaldehyde fixation. Due to the defined structure of this conjugated oligoelectrolyte we suspect that it will display organelle membrane selectivity, but this has to be further investigated.

The amphiphilic properties of conjugated oligoelectrolytes (COE) and their sensitivity to the polarity of their microenvironment lead to interesting aggregation behavior, in particular in their interaction with surfactants. Photoluminescence (PL) spectroscopy, liquid-phase atomic force microscopy, small-angle neutron scattering, small-angle X-ray scattering, and grazing-incidence X-ray diffraction were used to examine interactions between cationic p-phenylene vinylene based oligoelectrolytes and surfactants. These techniques indicate the formation of COE/surfactant aggregates in aqueous solution, and changes in the photophysical properties are observed when compared to pure aqueous solutions. We evaluate the effect of the charge of the surfactant polar headgroup, the size of the hydrophobic chain, and the role of counterions. At low COE concentrations (micromolar), it was found that these COEs display larger emission quantum efficiencies upon incorporation into micelles, along with marked blue-shifts of the PL spectra. This effect is most pronounced in the series of anionic surfactants, and the degree of blue shifts as a function of surfactant charge is as follows: cationic < nonionic < anionic surfactants. In anionic surfactants, such as sodium dodecyl sulfate (SDS), the PL spectra show vibronic resolution above the critical micelle concentration of the surfactant, suggesting more rigid structures. Scattering data indicate that in aqueous solutions, trimers appear as essentially 3-dimensional particles, while tetra- and pentamers form larger, cylindrical particles. When the molar ratio of nonionic C12E5 surfactant to 1,4-bis(4-{N,N-bis-[(N,N,N-trimethylammonium)hexyl]amino}-styryl)benzene tetraiodide (DSBNI) is close to one, the size of the formed DSBNI-C12E5 particles corresponds to the full coverage of individual oligomers. When these particles are transferred into thin films, they organize into a cubic in-plane pattern. If anionic SDS is added, the formed DSBNI-SDS particles are larger than expected for full surfactant coverage, and particles may thus contain several oligomers. This tendency is attributed to the merging of DSBNI oligomers due to the charge screening and, thus, reduced water solubility.

It is important to tailor biotic-abiotic interfaces in order to maximize the utility of bioelectronic devices such as microbial fuel cells (MFCs), electrochemical sensors and bioelectrosynthetic systems. The efficiency of electron-equivalent extraction (or injection) across such biotic-abiotic interfaces is dependent on the choice of the microbe and the conductive electrode material. In this contribution, we show that spontaneous intercalation of a conjugated oligoelectrolyte, namely 4,4'-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+), into the membranes of Escherichia coli leads to an increase in current generation in MFCs containing carbon-based electrodes. A combination of scanning electron microscopy (SEM) and confocal microscopy was employed to confirm the incorporation of DSSN+ into the cell membrane and biofilm formation atop carbon felt electrodes. Current collection was enhanced by more than 300% with addition of this conjugated oligoelectrolyte. The effect of DSSN+ concentration on electrical output was also investigated. Higher concentrations, up to 25 μM, lead to an overall increase in the number of charge equivalents transferred to the charge-collecting electrode, providing evidence in support of the central role of the synthetic system in improving device performance.

Variation in conjugated oligoelectrolyte (COE) repeat units is shown to affect the rate of COE insertion into mammalian membrane patches and membrane patch stabilities. These findings suggest that it is possible to find COE structures that do not destroy membranes while at the same time allow for more facile transmembrane movement of ions/substrates.

The conjugated oligoelectrolyte 4,4'-bis(4'-(N,N-bis(6 ''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+) has been employed to improve the performance of wastewater microbial fuel cells (MFCs) with respect to current generation and organic contaminant removal. The best performance was afforded by biocathode type MFCs run in the presence of DSSN+. Laser scanning confocal microscopy confirmed cellular uptake of DSSN+ in the biofilms.

Conjugated oligoelectrolytes are of emerging technological interest due to their recent function in the fabrication of optoelectronic devices, application in biosensors, and as species that facilitate transmembrane charge migration. Solubility in aqueous, or highly polar, solvents is important for many of these applications; however, there are few studies on how the self-assembly of conjugated oligoelectrolytes into multichromophore species influences linear and nonlinear optical properties. Here, we examine 1,4-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)benzene tetraiodide (DSBNI) in water, a conjugated oligoelectrolyte based on the distyrylbenzene framework. We find that DSBNI aggregation leads to increased fluorescence lifetimes, coupled with hypsochromic shifts, and larger two-photon absorption cross sections. Liquid atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) were used to image DSBNI aggregates and to confirm that the planar molecules stack to form nanocylinders above a critical aggregation concentration. Finally, small-angle neutron scattering (SANS) was used to quantify the aggregate dimensions in situ. Comparison of the results highlights that the hydrophilic mica surface used to image via liquid AFM and the high concentrations required for cryo-TEM facilitate the propagation of the cylinders into long fibers. SANS experiments are consistent with equivalent molecular packing geometry but lower aspect ratios. It is therefore possible to understand the evolution of optical properties as a function of concentration and aggregation and the general geometric features of the resulting supramolecular structures.

We report on the modification of membranes by incorporation of phenylenevinylene oligoelectrolytes with the goal of tailoring their optical and electronic properties and their applications. A water-soluble distyrylstilbene oligoelectrolyte (DSSN+), capped at each end with nitrogen bound, terminally charged pendant groups, was synthesized. The photophysical and solvatochromatic properties of DSSN+ and the shorter distyrylbenzene analogue DSBN+ were probed and found to be useful for characterizing insertion into membranes based on phospholipid vesicle systems. A combination of UV/visible absorbance and photoluminescence spectroscopies, together with confocal microscopy, were employed to confirm membrane incorporation. Examination of the emission intensity profile in stationary multilamellar vesicles obtained with a polarized excitation source provides insight into the orientation of these chromophores within lipid bilayers and indicates that these molecules are highly ordered, such that the hydrophobic electronically delocalized region positions within the inner membrane with the long molecular axis perpendicular to the bilayer plane. Cyclic voltammetry experiments provide evidence that DSSN+ and DSBN+ facilitate transmembrane electron transport across lipid bilayers supported on glassy carbon electrodes. Additionally, the interaction with living microorganisms was probed. Fluorescence imaging indicates that DSSN+ and DSBN+ preferentially accumulate within cell membranes. Furthermore, notable increases in yeast microbial fuel cell performance were observed when employing DSSN+ as the electron transport mediator.

Creating p–n junctions using semiconducting polymers has proved to be challenging because of difficulties in depositing semiconducting polymer films. Now, by using a cationic conjugated-polymer electrolyte and a neutral conjugated-polymer layer, devices with a fixed bilayer organic p–n junction and fast response times have been fabricated.