Theoretical Study on Electronic Transport Properties of Oligothiophene Molecular Devices

Based on the first-principles computational method and the elastic scattering Green＇s function theory, we have investigated the electronic transport properties of different oligothiophene molecular junctions theoretically. The numerical results show that the difference of geometric symmetries of the oligothiophene molecules leads to the difference of the contact configurations between the molecule and the electrodes, which results in the difference of the coupling parameters between the molecules and electrodes as well as the delocalization properties of the molecular orbitals. Hence, the series of oligothiophene molecular junctions display unusual conductive properties on the length dependence.

Theoretical study of structural and electronic properties of oligo(thiophene-phenylene)s in comparison with oligothiophenes and oligophenylenes

In this work, a quantum-chemical investigation on the structural and opto-electronic properties of oligo（thiophene-phenylene） （4TP） is carried out. The results are discussed in comparison with the properties of corresponding oligothiophene （8T） and oligophenylene （8P）. As the opto-electronic properties of this type of conducting polymers are governed by their electronic band gap, we shall also present a comparison among HOMO, LUMO and band gap energies of these three materials.

Organic Photovoltaic Properties Based on Oligothiophenes

The ITO/5T/PCH/Al1 device has a short circuit current of 3.4 mA/cm^2, an open circuit voltage of 2.1 V, fill fact of 27.5 % and photoelectric conversion efficiency of 2.5 %.

Luminescence Properties of Europium and Terbium Complexes with Pyridine or Bipyridine Linked Oligothiophene Ligand

With an aim to develop novel luminescence materials, europium and terbium complexes of 2, 5-(2-thiophene)-pyridine (TPY), 5, 5′-bis(5-(2, 2′-bithiophene))-2, 5-pyridine (B2TPY) and 5, 5′-bis(5-(2, 2′-bithiophene))-2, 2′-bipyridine (B2TBPY) were synthesized, and their luminescence properties were studied. The complexes exhibited ligand-sensitized emission, which was typical of Eu(Ⅲ) and Tb(Ⅲ) ions. The excitation spectra of Eu(Ⅲ) and Tb(Ⅲ) complexes with TPY (or B2TPY or B2TBPY) show similar bands as these with the ligands. It suggests that, the excitation energy is absorbed by TPY or B2TPY or B2TBPY, the energy transfers from its excited single state to its triplet state, and finally transfers from the ligands to Eu(Ⅲ) and Tb(Ⅲ) ions. The luminescence of Eu(Ⅲ) and Tb(Ⅲ) ions in the TPY or B2TPY or B2TBPY complexes indicates that the metal ions are efficiently excited by the absorbed energy from excitation of the ligands.

Organic photovoltaic devices with high open-circuit voltage based on oligothiophene derivatives

For the purpose of developing organic photovoltaic devices with good performance characteristics, we have fabricated two devices using 4T-CHO, 5T-CHO and PTCDA. The ITO/4T-CHO/PTCDA/Al device has a Voc of 2.45 V and photoelectric conversion efficiency of 2.76%. The ITO/ST-CHO/PTCDA/Al device has a Voc of 2.1 3V and photoelectric conversion efficiency of 2.90%. The two devices have higher Voc （2.45 and 2.13 V）. It is possible that intennolecular hydrogen bonding between -CHO group of nT-CHO and carboxylic dianhydride of PTCDA contribute to enhance the efficiency by promoting interracial electron transfer and eliminating the subconducting band trap sites.

A Rapid Solid-phase Synthesis to Soluble Oligothiophene Molecular Wires

A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity.

Photovoltaic molecules based on vinylene-bridged oligothiophene applied for bulk-heterojunction organic solar cells

We have synthesized two photovoltaic molecules（HEX-3TVT-ID and EH-3TVT-ID） based on vinylenebridged oligothiophene applied as donor for the solution-processable bulk-heterojunction organic solar cells（OSCs）. Vinylene unit was introduced as π-bridge in the oligothiophenes with 1,3-indenedione as end group and 4,4’-dihexyl-2,2’：5’,2’-terthiophene or 3’,4’-di（octan-3-yl）-2,2’：5’,2’-terthiophene as core,respectively. Due to the different substituent positions of the alkyl group relative to the vinylene unit in the terthiophene, HEX-3TVT-ID and EH-3TVT-ID show different optical and electrochemical properties, corresponding to the photovoltaic performance of the OSCs devices. The power conversion efficiency（PCE） of the OSCs based on a blend of HEX-3TVT-ID and PC71BM（1：0.8, weight ratio, 0.5% CN） reached 2.3%. In comparison, the OSCs based on the blend of EH-3TVT-ID and PC71BM in the weight ratio of 1：1 without the additive show a higher PCE of 2.7%, with a typically high VOC of 0.93 V, under the illumination of AM 1.5, 100 mW cm-2.

pFTAA: a high affinity oligothiophene probe that detects filamentous tau in vivo and in cultured neurons

Tauopathies describe a group of neurodegenerative diseases in which the protein tau,encoded by the gene MAPT,is aberrantly misfolded,leading to tau aggregation,neural dysfunction,and cell death（Spillantini and Goedert,2013）.In Alzheimer＇s disease（AD）,tau forms the characteristic intracellular neurofibrillary tangles（NFTs）,which are thought to be the major cause of neurodegeneration（Bloom,2014）.In other tauopathies,including frontotemporal dementia with Parkinsonism linked to chromo- some 17 （FTDP-17T）, corticobasal degeneration and progressive supranuclear palsy, there are specific forms of tau aggregates and filaments without any amyloid pathology, demonstrating tau＇s po- tent disease-causing potential （Spillantini and Goedert, 2013）. Tau is a microtubule （MT） binding protein, which becomes abnormally hyperphosphorylated on several residues prior/during the process of aggregation, thereby causing loss of its MT binding activity （Mandelkow and Mandelkow, 2012）.

Flexible organic photovoltaic devices based on oligothiophene derivatives

For the purpose of developing flexible organic photovoltaic devices, we have fabricated two flexible devices using 5-formyl- 2,2′：5′,2″：5″,2′″-quaterthiophene （4T-CHO）, 5-formyl-2,2′：5′, 2″：5″,2′″：5′″,2″″-quinquethiophene （5T-CHO） and 3,4,9,10-perylenetertracarboxylic dianhydride （PTCDA）. The PET-ITO/4T-CHO/PTCDA/A1 device has an open circuit voltage （Voc） of 1.56 V, photoelectric conversion efficiency of 0.77%. The PET-ITO/5T-CHO/PTCDA/A1 device has a Voc of 1.70 V, photoelectric conversion efficiency of 0.84%. The two flexible devices have high Voc （1.56 and 1.70 V）. It is possible that intermolecular hydrogen bonding between -CHO group of nT-CHO and carboxylic dianhydride of PTCDA contributes to enhancing the efficiency by promoting interfacial electron transfer and eliminating the subconducting band trap sites.

Self-assembled nanostructures of a series of linear oligothiophene derivatives adsorbed on surfaces

Many previous studies have shown that the molecular structures of oligothiophene derivatives including molecular skeleton and alkyl chains have a significant effect on their self-assemblies on the surface.In this work, a series of linear oligothiophene derivatives(DCV-n T-Hex, n = 3~11) modified with terminal dicyanovinyls and alkyl chains were adopted to further investigate the different assembly behaviors at liquid-solid interface by scanning tunneling microscopy(STM). Interestingly, via the hydrogen bonding and van der Waals interactions, DCV-3T-Hex formed zigzag and flower structures while DCV-n T-Hex(n = 4~11) formed lamellar structures. Density functional theory(DFT) calculations show that for the most energetically favorable configurations of DCV-n T-Hex, the different distribution of alkyl chains affected intermolecular interactions, and ultimately led to the different assembled structures. The zigzag and flower structures of DCV-3T-Hex had preferential thermodynamic stability compared to other structures of DCV-n T-Hex(n = 4~11). In addition, self-assembled nanostructures of DCV-n T-Hex molecules with even numbers(n = 4, 6, 8, 10) were overall more stable than those with odd numbers(n = 5, 7, 9,11), and the stability of the self-assembled structure was weakened with the extension of the molecular backbone, individually. The orientation of molecular alkyl chains was found to greatly affect the intermolecular interactions and thus leading to various self-assembly structures of DCV-n T-Hex(n = 3~11).

Adsorption of helical and saddle-shaped oligothiophenes on solid surface

The arrangement of oligothiophenes is essential for understanding the relationship between structure and properties particularly in the organic electronic field. The self-assembly behaviors of helical(TMS)2-[7]helicene(T1), naphthalene-cored double(TMS)2-[7]helicene(T2), and saddle-shaped cyclooctatetrathiophene(T3), its derivative α,α,α,α-tetraphenyl-cyclooctatetrathiophene(T4) on solid surface are firstly investigated by using a combination of scanning tunneling microscopy(STM) and density functional theory(DFT) calculation. 1,3,5-Tris(10-carboxydecyloxy)-benzene(TCDB) is selected to build flexible host networks to immobilize these oligothiophenes in order to capture their molecular adsorption images successfully. The observed monodisperse or polydisperse filling and long-range alignment of oligothiophenes are described based on the non-covalent interactions and commensurate structure between olihothiophene and cavity. We speculate that those molecularly defined alignments could lead to significantly understanding the application of such ordered monolayer in organic electronic devices.

The Key Role of Subtle Substitution for a High-Performance Ester-Modified Oligothiophene-Based Polymer Used in Photovoltaic Cells

In organic solar cells (OSCs), developing high-performing easily synthesized photoactive materials is essential for pursuing cost- effective balance. Herein, we have designed and synthesized a pair of wide-band-gap polymers (PBDE4T-0F and PBDE4T-2F), using the low synthesis cost dicarboxylic ester-substituted quaterthiophene as the building block. Despite the minor change of molecular structure for polymer PBDE4T-xF, the fluorine substituent in polymer PBDE4T-2F greatly enhances its interchain aggregation. The higher aggregation tendency of ester-modified polymer in solution is beneficial for reducing both the aggregate size and π-π stacking distance of blend film, which contribute to the highly efficient exciton dissociation and symmetric charge transport. An impressive power-conversion efficiency (PCE) of 16.1% is achieved for the PBDE4T-2F:BTP-eC9-based device, while its counterpart only delivers a PCE of 5.8% with distinctly lower short-circuit current density (J_(sc)) and fill factor. Notably, the aggregation effect of donor polymer has also been found to be associated with the energy level shifts, and thus the variation of charge transfer energy and voltage losses for blend system. The results suggest that simultaneously reduced voltage loss and increased J_(sc) can be expected by further finely tuning the aggregation behavior of the ester-modified oligothiophene-based donor polymer.

Photophysical and Electrochemical Properties of a Family of Oligothiophene Derivatives in Solution

The photophysical and electrochemical properties of a family of oligothiophene derivatives in solution were studied. It was found that the cyano and the vinyl group could increase fluorescence yield in solution, while the formyl and carboxyl group could decrease energy gap. With increasing the chain length of thiophene ring, the oxidation potential could be decreased.

SYNTHESIS, PROPERTIES AND ELECTROPOLYMERIZATION OF STAR-SHAPED OLIGOTHIOPHENES WITH HEXAKIS(FLUOREN-2-YL)BENZENE AS CORE

Star-shaped oligothiophenes with hexakis（fluoren-2-yl）benzene （HFB） as cores were designed and synthesized. Grafting thiophene units to HFB results in a bond flattening of the core, and makes the molecules a flipping-twist shape. Their thermal, photophysical and electrochemical properties were studied. Highly cross-linked conjugated polymers can be produced by electropolymerization of T1-T3.

Effect of End-capping Functional Groups on the Optoelectronic Properties of Oligothiophene Derivatives

Five novel oligothiophene derivatives end-capped by different functional groups （R=ethoxyl （EtOP3T）, me- thylsulfanyl （MSP3T）, acetyl （AcP3T）, methylsulfonyl （MSO2P3T） and biphenyl （BP3T） groups） were synthe- sized. They were characterized by nuclear magnetic resonance （IH NMR）, mass spectrometry （MS） and Fourier transform Infra-red spectra （IR）. The relationship between end-capping functional groups and optoelectronic prop- erties of them was investigated. It was found that the compound with sulfonyl group in the molecular structure （MSOeP3T） shows the highest oxidation stability （also supported by theoretical calculations） and best thermal sta- bility among the five compounds. The results of scanning electron microscope （SEM） interpret that MSOzP3T dis- plays excellent ability of self-film forming. This reveals that it could be a potential candidate for thin film material. The liquid crystal property of MSO2P3T was characterized by polarized optical microscopy analysis （POM） and X-ray diffraction （XRD）. The results of this paper provide useful information for the design of tailored oligothio- phene derivatives for devices.

Spatially resolved chiroptical study of thin films of benzo[1,2-b:4,5-b’]dithiophene-based oligothiophenes by synchrotron radiation electronic circular dichroism imaging(SR-ECDi)technique

The study of the chiroptical properties of thin-film samples of two chiral benzo[1,2-b:4,5-b’]dithiophene-based oligothiophenes with optoelectronic properties was carried out at Diamond B23 beamline using the synchrotron radiation electronic circular dichroism imaging(SR-ECDi)facility.The experimental results support the hypothesis that the non-reciprocal circularly polarized absorption observed in these materials is due to the combined linear dichroism and linear birefringence contributions.The mapping at 50-μM spatial resolution revealed that several species coexist in the mesoscopic chiral domains likely due to different aggregated phases,which were identified in the films by SR-ECDi but could not be detected with benchtop ECD instruments.

Alzheimer’s Disease Aβ-Amyloid Plaque Morphology Varies According to APOE Isotype

Background: The apolipoprotein E (APOE, gene;apoE, protein) ε4 allele is the most commonly identified genetic risk factor for typical late-onset sporadic Alzheimer’s disease (AD). Each APOE ε4 allele roughly triples the relative risk for AD compared to that of the reference allele, APOE ε3. Methods: We have employed hyperspectral fluorescence imaging with an amyloid-specific, conformation-sensing probe, p-FTAA, to elucidate protein aggregate structure and morphology in fresh frozen prefrontal cortex samples from human postmortem AD brain tissue samples from patients homozygous for either APOE ε3 or APOE ε4. Results: As expected APOE ε4/ε4 tissues had a significantly larger load of CAA than APOE ε3/ε3. APOE isoform-dependent morphological differences in amyloid plaques were also observed. Amyloid plaques in APOE ε3/ε3 tissue had small spherical cores and large coronas while amyloid plaques in APOE ε4/ε4 tissues had large irregular and multi-lobulated plaques with relatively smaller coronas. Despite the different morphologies of their cores, the p-FTAA stained APOE ε3/ε3 amyloid plaque cores had spectral properties identical to those of APOE ε4/ε4 plaque cores. Conclusions: These data support the hypothesis that one mechanism by which the APOE ε4 allele affects AD is by modulating the macrostructure of pathological protein deposits in the brain. APOE ε4 is associated with a higher density of amyloid plaques (as compared to APOE ε3). We speculate that multilobulated APOE ε4-associated plaques arise from multiple initiation foci that coalesce as the plaques grow.

Structural Analysis of Thermally-Annealed Bulk Heterojunction Films Based on Sexithiophene and Fullerene

Recently, power conversion efficiencies of organic photovoltaics based on small molecules have been dramatically improved by means of the bulk heterojunction (BHJ) structure. Moreover, to optimize photovoltaic performance, thermal annealing treatments have often been used because of the simplicity of the process. However, the elucidation of effects of thermal annealing treatment on BHJ film structure based on small molecules is still not enough. Here, we report the results of structural analysis with synchrotron radiation of α-sexithiophene:fullerene BHJ films before and after thermal annealing treatment. In particular, the open-circuit voltage was increased to as high as 0.72 V;moreover, the BHJ films based on α-sexithiophene and fullerene were also clearly crystallized by the thermal annealing treatment. In this study, we found that the optimal crystal size existed in BHJ films for high-performance organic photovoltaics.

Effect of Self-Assembled Monolayers on the Performance of Organic Photovoltaic Cells

The improvement of the performance of organic photovoltaic cells (OPVCs) and the photogeneration process in these devices may occur via multiple mechanisms depending on their structure and/or architecture. For this purpose we investigate how self-assembled monolayers of thiol molecules (C12H25SH and 3T(CH2)6SH) and benzoic acid molecules (ABA and NBA) affect the efficiency and the photogeneration of free carriers in a sexithiophene based photovoltaic cells. Firstly, we provide the results of absorption spectra for samples with SAM of thiol that show there effect on orientation of 6T molecules on these structures and the organization degree of the thiol molecules on ITO substrate. Afterward, we describe from current vs. applied voltage after illumination, the enhancement of the performance of these cells. In the second, we study the effect of SAM of benzoic acids molecules on the photovoltaic behavior. A theoretical model is used for quantitative description of the open circuit voltage as a function of carrier’s generation rates at the electrodes. The results of I-V characterization under illumination show that open circuit voltage as well as short circuit current is dramatically affected by the dipolar layer. The orientation and the magnitude of dipole moment of benzoic acid molecules are the crucial factors that affect the organic photovoltaic parameters.