Understanding the evolution of the Raman spectra of molecularly p-doped poly(3-hexylthiophene-2,5-diyl): signatures of polarons and bipolarons

Molecular doping is a key process to increase the density of charge carriers in organic semiconductors. Doping-induced charges in polymer semiconductors result in the formation of polarons and/or bipolarons due to the strong electron-vibron coupling in conjugated organic materials. Identifying the nature of charge carriers in doped polymers is essential to optimize the doping process for applications. In this work, we use Raman spectroscopy to investigate the formation of charge carriers in molecularly doped poly(3-hexylthiophene-2,5-diyl) (P3HT) for increasing dopant concentration, with the organic salt dimesityl borinium tetrakis(penta-fluorophenyl)borate (Mes₂B⁺ [B(C₆F₅)₄]^-) and the Lewis acid tris(pentafluorophenyl)borane [B(C₆F₅)₃]. While the Raman signatures of neutral P3HT and singly charged P3HT segments (polarons) are known, the Raman spectra of doubly charged P3HT segments (bipolarons) are not yet sufficiently understood. Combining Raman spectroscopy measurements on doped P3HT thin films with first-principles calculations on oligomer models, we explain the evolution of the Raman spectra from neutral P3HT to increasingly doped P3HT featuring polarons and eventually bipolarons at high doping levels. We identify and explain the origin of the spectral features related to bipolarons by tracing the Raman signature of the symmetric collective vibrations along the polymer backbone, which - compared to neutral P3HT - redshifts for polarons and blueshifts for bipolarons. This is explained by a planarization of the singly charged P3HT segments with polarons and rather high order in thin films, while the doubly charged segments with bipolarons are located in comparably disordered regions of the P3HT film due to the high dopant concentration. Furthermore, we identify additional Raman peaks associated with vibrations in the quinoid doubly charged segments of the polymer. Our results offer the opportunity for readily identifying the nature of charge carriers in molecularly doped P3HT while taking advantage of the simplicity, versatility, and non-destructive nature of Raman spectroscopy.

Band gap engineering in blended organic semiconductor films based on dielectric interactions

Blending organic molecules to tune their energy levels is currently being investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy and electron affinity can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here we show that the energy gap of organic semiconductors can also be tuned by blending. We use oligothiophenes with different numbers of thiophene rings as an example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller, effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this energy-level engineering strategy for optoelectronic devices.

Lameness in fattening pigs - Mycoplasma hyosynoviae, osteochondropathy and reduced dietary phosphorus level as three influencing factors: a case report

BACKGROUND

Multiple diagnostic procedures, their results and interpretation in a case with severe lameness in fattening pigs are described. It is shown that selected diagnostic steps lead to identification of various risk factors for disease development in the affected herd. One focus of this case report is the prioritization of diagnostic steps to verify the impact of the different conditions, which finally led to the clinical disorder. Assessing a sufficient dietary phosphorus (P) supply and its impact on disease development proved most difficult. The diagnostic approach based on estimated calculation of phosphorus intake is presented in detail.

CASE PRESENTATION

On a farrow-to-finishing farm, lameness occurred in pigs with 30-70 kg body weight. Necropsy of three diseased pigs revealed claw lesions and alterations at the knee and elbow joints. Histologic findings were characteristic of osteochondrosis. All pigs were positively tested for Mycoplasma hyosynoviae in affected joints. P values in blood did not indicate a P deficiency, while bone ashing in one of three animals resulted in a level indicating an insufficient mineral supply. Analysis of diet composition revealed a low phosphorus content in two diets, which might have led to a marginal P supply in individuals with high average daily gains with respect to development of bone mass and connective tissue prior to presentation of affected animals. Finally, the impact of dietary factors for disease development could not be evidenced in all submitted animals in this case.

CONCLUSIONS

Mycoplasma (M.) hyosynoviae was identified to be an important etiologic factor for disease. Other, non-infectious factors, such as osteochondrosis and claw lesions might have favored development of lameness. In addition, a relevant marginal P supply for pigs was found in a limited time period in a phase of intense growing, but the potential interaction with infection by M. hyosynoviae is unknown. The presented case of severe lameness in fattening pigs revealed that three different influences presumably act in pathogenesis. Focusing only on one factor and ignoring others might be misleading regarding subsequent decision-making for prevention and therapy. Finally, clinical symptoms disappeared after some changes in diet composition and anti-inflammatory treatment of individual animals.

An Organic Borate Salt with Superior p-Doping Capability for Organic Semiconductors

Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto-) electronics. Beyond single-component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes2B+; Mes: mesitylene) and the tetrakis(penta-fluorophenyl)borate anion [B(C6F5)4]- is demonstrated as p-type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes2B+, and the positive charge on the polymer is stabilized by [B(C6F5)4]-. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C6F5)4]- even enables the stabilization of polarons and bipolarons in poly(3-hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes2B+[B(C6F5)4]- is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.

Corrigendum: Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors

This corrects the article DOI: 10.1038/nmat5027.

Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors

Chemical doping of organic semiconductors using molecular dopants plays a key role in the fabrication of efficient organic electronic devices. Although a variety of stable molecular p-dopants have been developed and successfully deployed in devices in the past decade, air-stable molecular n-dopants suitable for materials with low electron affinity are still elusive. Here we demonstrate that photo-activation of a cleavable air-stable dimeric dopant can result in kinetically stable and efficient n-doping of host semiconductors, whose reduction potentials are beyond the thermodynamic reach of the dimer's effective reducing strength. Electron-transport layers doped in this manner are used to fabricate high-efficiency organic light-emitting diodes. Our strategy thus enables a new paradigm for using air-stable molecular dopants to improve conductivity in, and provide ohmic contacts to, organic semiconductors with very low electron affinity.

Charge-transfer crystallites as molecular electrical dopants

Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi–Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites—rather than individual acceptor molecules—should be regarded as the dopants in such systems.

The fundamental mechanisms of doping organic semiconductors are poorly understood compared with their inorganic counterparts. Here, the authors demonstrate that small conjugated molecules and conjugated polymers exhibit fundamentally different phenomena upon doping despite similar compositions.

Energy-Level Engineering at ZnO/Oligophenylene Interfaces with Phosphonate-Based Self-Assembled Monolayers

We used aromatic phosphonates with substituted phenyl rings with different molecular dipole moments to form self-assembled monolayers (SAMs) on the Zn-terminated ZnO(0001) surface in order to engineer the energy-level alignment at hybrid inorganic/organic semiconductor interfaces, with an oligophenylene as organic component. The work function of ZnO was tuned over a wide range of more than 1.7 eV by different SAMs. The difference in the morphology and polarity of the SAM-modified ZnO surfaces led to different oligophenylene orientation, which resulted in an orientation-dependent ionization energy that varied by 0.7 eV. The interplay of SAM-induced work function modification and oligophenylene orientation changes allowed tuning of the offsets between the molecular frontier energy levels and the semiconductor band edges over a wide range. Our results demonstrate the versatile use of appropriate SAMs to tune the energy levels of ZnO-based hybrid semiconductor heterojunctions, which is important to optimize its function, e.g., targeting either interfacial energy- or charge-transfer.

Final results of phase II trial of doxorubicin HCl liposome injection followed by bexarotene in advanced cutaneous T-cell lymphoma

BACKGROUND

High response rates for doxorubicin HCl liposome injection (DLI) in cutaneous T-cell lymphoma (CTCL) have been reported with vague criteria until recently. Approximately 50% of CTCL patients respond to bexarotene (Bex).

PATIENTS AND METHODS

A phase II trial was carried out to clarify the true overall response rate (ORR) for DLI and to assess the role of sequential Bex. Patients were treated with DLI 20 mg/m(2) i.v. every 2 weeks for 16 weeks (8 doses) followed by 16 weeks with Bex 300 mg/m(2) orally. Response assessments were carried out after 16 (DLI) and 32 weeks (Bex). Skin responses were measured by the modified Severity-Weighted Assessment Tool (mSWAT) and the Composite Assessment of Index Lesion Severity (CA).

RESULTS

Thirty-seven patients were treated: stage IV (22, 8 with Sézary syndrome), IIB (10), earlier stage refractory to skin-directed therapies or radiation therapy (5). For 34 assessable patients: ORR 14/34 [41%: partial response (PR) 12, clinical complete response (CCR) 2]. Maximum responses were all seen after 16 weeks DLI. Median progression-free survival (PFS) was 5 months. There were 22 deaths: 21 of disease and 1 of heart failure. Twenty-seven grade 3 and 5 grade 4 toxic events were observed.

CONCLUSION(S)

With strict criteria, DLI ORR is among the highest reported for single agents in CTCL. Sequential Bex did not increase the response rate or duration.

C-reactive protein induced activation of MAP-K and RANTES in human renal distal tubular epithelial cells in vitro

AIMS

C-reactive protein (CRP) is a component of the acute-phase reaction to inflammation, severe tissue injury, and infection. Investigations have shown that CRP concentration is highly increased in the urine during acute renal graft dysfunction and, therefore, may affect tubular cell metabolism. Nevertheless, no data about the effects of CRP on human renal tubular epithelial cells are available.

METHODS

Human renal distal tubular cells (DTC) were isolated immunomagnetically and cultured. Cells were stimulated with affinity chromatography pure native CRP from human ascites (10 - 0.001 microg/ml). Phosphorylation of MAP-K was assessed by Westernblot analysis. Release of RANTES and interleukin-6 was evaluated with an enzyme immunoassay. Cytotoxic effects of CRP were determined by a commercially available Live/Dead assay and MTT assay. Effects on cell proliferation were analyzed by a fluorimetric assay.

RESULTS

Westernblot analysis clearly showed that CRP activates the MAP-K pathway of DTC. CRP upregulated RANTES expression of DTC in a significant and dose-dependent manner. CRP (10 microg/ml) induced a 12.3-fold upregulation, CRP 1 or 0.1 microg/ml induced a 6.3-/2.8-fold RANTES upregulation, respectively. Interleukin-6 synthesis was not influenced. Cytotoxic, proliferative or apoptotic effects were not observed at the concentrations used.

CONCLUSIONS

We demonstrated an activating effect of CRP on DTC in vitro. In vivo, this effect of CRP might be part of the immune activation cascade during episodes of renal graft rejection or bacterial infections.

Biosynthesis of cladospirone bisepoxide, a member of the spirobisnaphthalene family

The biosynthesis of cladospirone bisepoxide (1) was investigated by feeding 13C-labeled acetate to growing cultures of the fungus Sphaeropsidales sp. (strain F-24'707). 13C NMR spectral analysis demonstrated the polyketide origin of both naphthalene units. The origin of two epoxide oxygens was confirmed as from air by cultivation of the strain in an 18O2-enriched atmosphere. The [18O]incorporation pattern into palmarumycin C12 (11), the putative precursor of 1 led to the hypothesis that the carbonyl oxygen of 1 is derived from water by exchange of an oxygen atom. Inhibition of the biosynthesis of 1 with tricyclazole, an inhibitor of the 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis, confirmed the connection of both biosynthetic pathways.

Healthcare reform: it's working in Oregon

Oregon is beginning to operate a highly controversial program with explicit definitions of coverage. Oregon's Director of the Health Plan, Jean Thorne, has focused on the national and state political attention that Oregon is receiving and knows that "...there are many people who are waiting for us to fail." Thorne has requested that we keep our focus on making major changes to improve the chance that more people in poverty will receive coverage. We continue to believe that the Oregon Health Plan will improve overall healthcare in our state and serve as a blueprint for others to study and improve.