Oligothiophenes and conducting metallopolymers : fundamental studies and development of functional materials

textDiimine rhenium(I) tricarbonyl complexes are known as phosphorescent emitters and electro- and photocatalysts for the reduction of CO₂ to CO. Conducting metallopolymers containing this rhenium(I) moiety should not only retain the photoluminescent and catalytic properties of the complex but also gain the conductivity, processability, and mechanical flexibility typical of [pi]-conjugated polymers. A series of tricarbonyl rhenium(I) diimine-type monomers and metallopolymers have been prepared. Appended to the ligands are thiophene and 3,4-ethylenedioxythiophene (EDOT) groups for electropolymerization of the metal complexes. UV-Vis absorption and emission spectroscopy studies of the monomers indicate that light emission originates from triplet ligand-centered (³LC) [pi] [right arrow] [pi]* and triplet metal-to-ligand charge transfer (³MLCT) excited states. Additionally, both the monomers and metallopolymers show electrocatalytic activity towards the reduction of CO₂ to CO. Furthermore, the EDOT-functionalized diimine-type ligand (EDOT₂-BPP) also serves as a good sensitizing ligand for luminescent lanthanide emission. A series of lanthanide complexes that utilize tris([beta]-diketonates) and EDOT₂-BPP ligands have been synthesized and studied using X-ray crystallography and photophysical techniques. Large quantum yields and microsecond lifetimes were found for the EuIII and SmIII complexes. Complexes of TbIII were found to have weak luminescent emission due to the less-than-optimal energy gap between the sensitizing ligands and the excited state of the TbIII ion. Oligothiophenes are models for polymeric systems because of solution processability, controlled chain length, and a well-defined structure. We have synthesized a library of alkyl and polyfluoroalkyl-substituted oligothiophenes to study how molecular structure, long-range order, spatial orientation, and varying degree of electronic coupling between molecules influences charge separation in photovoltaics. These oligoalkylthiophenes have been characterized by X-ray diffraction, photophysical methods, electrochemistry, and UV-Vis and EPR spectroscopies. Although the electronic properties of these oligoalkylthiophenes do not vary with alkyl group, aggregates of oligooctylthiophene, made through solution processing, have distinct morphologies with varying amounts of electronic disorder. The extent of electronic disorder within the aggregate is determined by comparing the suppression of the 0-0 vibronic band in the fluorescence spectra to that of the non-aggregated parent molecule. This extent of electronic disorder was correlated with the local contact potential of individual aggregates through Kelvin probe force microscopy (KPFM) measurements.Chemistr

Episodic, transient systemic acidosis delays evolution of the malignant phenotype: Possible mechanism for cancer prevention by increased physical activity

Background: The transition from premalignant to invasive tumour growth is a prolonged multistep process governed by phenotypic adaptation to changing microenvironmental selection pressures. Cancer prevention strategies are required to interrupt or delay somatic evolution of the malignant invasive phenotype. Empirical studies have consistently demonstrated that increased physical activity is highly effective in reducing the risk of breast cancer but the mechanism is unknown. Results: Here we propose the hypothesis that exercise-induced transient systemic acidosis will alter the in situ tumour microenvironment and delay tumour adaptation to regional hypoxia and acidosis in the later stages of carcinogenesis. We test this hypothesis using a hybrid cellular automaton approach. This model has been previously applied to somatic evolution on epithelial surfaces and demonstrated three phases of somatic evolution, with cancer cells escaping in turn from the constraints of limited space, nutrient supply and waste removal. In this paper we extend the model to test our hypothesis that transient systemic acidosis is sufficient to arrest, or at least delay, transition from in situ to invasive cancer. Conclusions: Model simulations demonstrate that repeated episodes of transient systemic acidosis will interrupt critical evolutionary steps in the later stages of carcinogenesis resulting in substantial delay in the evolution to the invasive phenotype. Our results suggest transient systemic acidosis may mediate the observed reduction in cancer risk associated with increased physical activity

Anion-Dependent Self-Assembly of Near-Infrared Luminescent 24- and 32-Metal Cd–Ln Complexes with Drum-like Architectures

Two series of 4d–4f clusters [Ln₈Cd₂₄L₁₂­(OAc)₄₈] and [Ln₆Cd₁₈L₉Cl₈₍₁₀₎­(OAc)₂₈₍₂₆₎] (Ln = Nd, Gd, Er, and Yb) with novel drum-like structures were prepared using a flexible Schiff base ligand. Their NIR luminescence properties were determined

Anion-Dependent Self-Assembly of Near-Infrared Luminescent 24- and 32-Metal Cd–Ln Complexes with Drum-like Architectures

Two series of 4d–4f clusters [Ln₈Cd₂₄L₁₂­(OAc)₄₈] and [Ln₆Cd₁₈L₉Cl₈₍₁₀₎­(OAc)₂₈₍₂₆₎] (Ln = Nd, Gd, Er, and Yb) with novel drum-like structures were prepared using a flexible Schiff base ligand. Their NIR luminescence properties were determined

The Effects of Aggregation on Electronic and Optical Properties of Oligothiophene Particles

Solution processing of oligothiophene molecules is shown to produce a range of particles with distinct morphologies. Once isolated on a substrate, the optical and electronic properties of individual particles were studied. From polarized scanning confocal microscopy experiments, distinct particles that are identifiable by shape were shown to have similar emission spectra except in regard to the 0–0 vibronic band intensity. This suppression of the 0–0 vibronic band correlates to the amount of energetic disorder present in a weakly coupled H-aggregate. The studied particles ranged from moderate to almost complete suppression of the 0–0 vibronic band when compared to the emission spectrum of the isolated molecule in solution. All particles were found to have a high degree of geometric order (molecular alignment) as observed from the fluorescence dichroism (FD) values of around 0.7–0.8 for all the studied morphologies. The structural and electronic properties of the particles were investigated with Kelvin probe force microscopy (KPFM) to measure the local contact potential (LCP) difference, a quantity that is closely related to the differences in intermolecular charge distribution between the oligothiophene particles. The LCP was found to vary by as much as 70 mV between different oligothiophene particles and a trend was observed that correlated the LCP changes with the amount of energetic disorder present, as signified by the suppression of the 0–0 vibronic peak in the emission spectra. Combined polarized scanning confocal microscopy studies, along with KPFM measurements, help to provide fundamental insights into the role of morphology, molecular packing, and intermolecular charge distributions in oligiothiophene particles

Resonance Raman Spectroscopy of the T₁ Triplet Excited State of Oligothiophenes

The characterization of triplet excited states is essential for research on organic photovoltaics and singlet fission. We report resonance Raman spectra of two triplet oligothiophenes with <i>n</i>-alkyl substituents, a tetramer and hexamer. The spectra of the triplets are more complex than the ground state, and we find that density functional theory calculations are a useful starting point for characterizing the bands. The spectra of triplet tetrathiophene and hexathiophene differ significantly from one another. This observation is consistent with a T₁ excitation that is delocalized over at least five rings in long oligomers. Bands in the 500–800 cm^–1 region are greatly diminished for an aggregated sample of hexathiophene, likely caused by fast electronic dephasing. These experiments highlight the potential of resonance Raman spectroscopy to unequivocally detect and characterize triplets in thiophene materials. The vibrational spectra can also serve as rigorous standards for evaluating computational methods for excited-state molecules

Synthesis, Characterization, and Photophysical Properties of a Thiophene-Functionalized Bis(Pyrazolyl) Pyridine (BPP) Tricarbonyl Rhenium(I) Complex

A bromo tricarbonyl rhenium(I) complex with a thiophene-functionalized bis(pyrazolyl) pyridine ligand (L), ReBr(L)(CO)(3) (1), has been synthesized and characterized by variable temperature and COSY 2-D H-1 NMR spectroscopy, single-crystal X-ray diffraction, and photophysical methods. Complex 1 is highly luminescent in both solution and solid-state, consistent with phosphorescence from an emissive (MLCT)-M-3 excited state with an additional contribution from a LC (3)(pi ->pi*) transition. The single-crystal X-ray diffraction structure of the title ligand is also reported.Robert A. Welch Foundation F-1631Petroleum Research Fund 47022-G3National Science Foundation CHE-0639239, CHE-0741973, CHE-0847763American Heart Association 0765078YUT-CNMUT-AustinChemistr