Tuning and Tracking of Coherent Shear Waves in Molecular Films.

We have determined the time-dependent displacement fields in molecular sub-micrometer thin films as response to femtosecond and picosecond laser pulse heating by time-resolved X-ray diffraction. This method allows a direct absolute determination of the molecular displacements induced by electron-phonon interactions, which are crucial for, for example, charge transport in organic electronic devices. We demonstrate that two different modes of coherent shear motion can be photoexcited in a thin film of organic molecules by careful tuning of the laser penetration depth relative to the thickness of the film. The measured response of the organic film to impulse heating is explained by a thermoelastic model and reveals the spatially resolved displacement in the film. Thereby, information about the profile of the energy deposition in the film as well as about the mechanical interaction with the substrate material is obtained.

Injectable iodine-125 labeled tissue marker for radioactive localization of non-palpable breast lesions.

We have developed a 125I-radiolabeled injectable fiducial tissue marker with the potential to replace current methods used for surgical guidance of non-palpable breast tumors. Methods in routine clinical use today such as radioactive seed localization, radio-guided occult lesion localization and wire-guided localization suffers from limitations that this injectable fiducial tissue marker offers solutions to. The developed 125I-radiolabeled injectable fiducial tissue marker is based on highly viscous sucrose acetate isobutyrate. The marker was readily inserted in NMRI mice and proved to be spatially well-defined and stable over a seven day period with excellent CT contrast (>1500 HU), enabling fluoroscopic visualization of the marker during placement. The radioactivity remains strongly associated with the marker during the implantation period, which limits exposure to healthy tissue. Biodistribution studies show that there is negligible radioactivity in all non-tumor tissues sampled, with the exception of the thyroid gland, where limited accumulation was observed (0.06% of injected dose after 7 days). Based on the excellent performance of the marker and the fact that it can be delivered through thin hypodermic needles (≥27G), the marker holds great promise for clinical application, since patient discomfort is reduced significantly compared to current methods. STATEMENT OF SIGNIFICANCE: A new type of tissue marker for local administration to non-palpable breast tumors has been developed. The surgical guidance marker is based on derivatives of the biomaterial sucrose acetate isobutyrate and unlike currently used markers it is injectable in the tissue using thin needles, reducing the discomfort to the patients significantly. The marker confers CT contrast and has radioactive properties, meaning it also could find use in brachytherapy. The design of the iodine-125 labeled fiducial tissue marker enables control of dosimetry as well as a choice of iodine isotope used. The marker is anticipated to be clinical applicable due to its contrast performance in mice and its potential for enhanced flexibility in surgical procedures, compared to current methods.

Excited state kinetics of anthracene-bridge-aniline intramolecular exciplexes.

We report on the synthesis and characterization of fluorescent halogen substituted anthracene-bridge-aniline (ABA) supermolecules that undergo structural reorganization on photoexcitation to form transient complexes. The syntheses were achieved in high yields on a large scale and the molecular structures were confirmed by single crystal X-ray diffraction. The photophysics of the ABA supermolecules were investigated using steady state and time resolved optical spectroscopy. Despite the presence of heavy atoms the series of ABA molecules have high quantum yields of fluorescence from both a locally excited anthracene state (LE) and an excited state complex (exciplex, EP) in non-polar solvents. The kinetics of the excited state processes were established in decalin from the time-resolved emission, and was shown to be strongly influenced by an electron-transfer state (ET). For quantitative studies of the excited state dynamics, the presence of this state required the development of a numerical three-excited-state kinetic model to replace the commonly used two-excited-state model. The experimental results shows that the reaction rates are strongly influenced both by substituents and solvent, illustrating the importance of including all relevant states in the kinetic modeling. Ultimately it is established that the excited state dynamics can conveniently be followed by optical methods, and the applicability of the system as a model system in time-resolved X-ray scattering experiments is discussed.

Counterions control whether self-assembly leads to formation of stable and well-defined unilamellar nanotubes or nanoribbons and nanorods.

Self-assembly of the amphiphilic π-conjugated carbenium ion ATOTA-1(+) in aqueous solution selectively leads to discrete and highly stable nanotubes or nanoribbons and nanorods, depending on the nature of the counterion (Cl(-) vs. PF6(-), respectively). The nanotubes formed by the Cl(-) salt illustrate an exceptional example of a structural well-defined (29±2 nm in outer diameter) unilamellar tubular morphology featuring π-conjugated functionality and high stability and flexibility, in aqueous solution.

Diazadioxa[8]circulenes: planar antiaromatic cyclooctatetraenes.

In this paper we describe a new class of antiaromatic planar cyclooctatetraenes: the diazadioxa[8]circulenes. The synthesis was achieved by means of a new acid-mediated oxidative dimerization of 3,6-dihydroxycarbazoles to yield the diazadioxa[8]circulenes in high yields. The synthetic protocol appears to be general, and is a one-pot transformation in which two C-C bonds and two C-O bonds are formed with the loss of two molecules of water. We also present a detailed characterization of the optical and electrochemical properties of this new class of stable planar cyclooctatetraenes. The properties of the diazadioxa[8]circulenes are compared with the properties of isoelectronic tetraoxa[8]circulenes and azatrioxa[8]circulenes. We discuss the antiaromatic nature of the planar central cyclooctatetraene moiety. The antiaromatic nature of the planar cyclooctatetraenes was studied by using computational methods (NICS calculations), and these calculations reveal that the central eight-membered ring has antiaromatic character.

Azatrioxa[8]circulenes: planar anti-aromatic cyclooctatetraenes.

We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.

A triptycene-based approach to solubilising carbon nanotubes and C60.

We describe herein the synthesis of a triptycene-based surfactant designed with the ability to solubilise single-walled carbon nanotubes (SWNTs) and C(60) in water through non-covalent interactions. Furthermore, an amphiphilic naphthalene-based surfactant with the same ability to solubilise SWNTs and C(60) has also been prepared. The compounds synthesised were designed with either two ionic or non-ionic tails to ensure a large number of supramolecular interactions with the solvent, thereby promoting strong solubilisation. The surfactants produced stable suspensions in which the SWNTs are dispersed and the surfactant/SWNT complexes formed are stable for more than one year. UV/Vis/NIR absorption spectroscopy, TEM and AFM were employed to probe the solubilisation properties of the dispersion of surfactants and SWNTs in water.

Base-assisted one-pot synthesis of N,N',N"-triaryltriazatriangulenium dyes: enhanced fluorescence efficiency by steric constraints.

In this paper we report the first synthesis of cationic N,N',N"-triaryltriazatriangulenium dyes (Ar(3)-TATA(+)). Previously, only alkyl-substituted triazatriangulenium derivatives (R(3)-TATA(+)) were known, a consequence of the low reactivity of anilines in the aromatic nucleophilic substitution reaction leading to the formation of the TATA(+) core. The synthesis of Ar(3)-TATA(+) was achieved by heating the tris(2,6-dimethoxyphenyl)methylium ion (DMP(3)C(+)) in various anilines in the presence of NaH. In the solvent-free reaction all three aryl substituents could be introduced despite the low reactivity of the anilines. The symmetric Ar(3)-TATA(+) derivatives with Ar = phenyl (2), 4-methoxyphenyl (3), and 4-bromophenyl (4) were synthesized. Single crystal structures of 2 and 4 were obtained as BF(4)(-) salts, where torsional angles larger than 80° were observed between the TATA(+) chromophore and the aryl substituents. The photophysical properties were studied in solution and in thin films. The results show that the Ar(3)-TATA(+) dyes have a surprising 3-fold increase in fluorescence quantum yields when compared to the parent alkyl-substituted R(3)-TATA(+) salts. With a high quantum yield (>50%) and emission in the red (λ(fl) = 560 nm) the Ar(3)-TATA(+) dyes represent a promising new addition to the family of superstable cationic triangulenium dyes. Additionally, the synthesized tribromo derivative 4 is shown to be a potential triagonal synthon for polymers and other macromolecules.

Microporous polycarbazole with high specific surface area for gas storage and separation.

Microporous polycarbazole via straightforward carbazole-based oxidative coupling polymerization is reported. The synthesis route exhibits cost-effective advantages, which are essential for scale-up preparation. The Brunauer-Emmett-Teller specific surface area for obtained polymer is up to 2220 m(2) g(-1). Gas (H(2) and CO(2)) adsorption isotherms show that its hydrogen storage can reach to 2.80 wt % (1.0 bar and 77 K) and the uptake capacity for carbon dioxide is up to 21.2 wt % (1.0 bar and 273 K), which show a promising potential for clean energy application and environmental field. Furthermore, the high selectivity toward CO(2) over N(2) and CH(4) makes the obtained polymer possess potential application in gas separation.

Solution-based fabrication of single-crystalline arrays of organic nanowires.

Organic single-crystalline nanowire arrays, with a length of several hundreds of micrometers and controllable width, are grown on a substrate surface by vertically pulling the substrate out of an organic solution of the molecule of interest. Optical microscopy and atomic force microscopy show that the large-scale arrays are oriented parallel to the pulling direction and are well adhered to the substrate surface. Cross-polarized microscopy, polarized UV-vis absorption, and grazing incidence X-ray diffraction confirm that the arrays have high crystal quality. On the basis of this method, the fabrication of organic devices is realized in one step. The results presented here for three different small molecules show the promising potential of this facile solution-based process for the growth of high-quality organic semiconductors, the fabrication of high-density and high-performance devices, and the fabrication of controlled assemblies of nanoscale circuits for fundamental studies and future applications.

Bis[S-6-(2,2:6',2''-terpyridin-4'-yloxy)hexyl thioacetate]manganese(II) bis(hexafluorophosphate).

The structure of a manganese(II) complex of terpyridine functionalized with acetylsulfanyl-terminated hexyloxy chains, [Mn(C(23)H(25)N(3)O(2)S)(2)](PF(6))(2), is described. This type of complex is of interest in the study of single-molecule transport properties in open-shell systems. The manganese coordination environment is distorted octahedral but, importantly, with no larger deviations from the idealized geometry than those observed for other metal-terpyridine complexes. The Mn-N bond lengths range from 2.192 (2) to 2.272 (3) A. The title compound crystallizes with the cation and anions all on general positions, with the hexafluorophosphate anions exhibiting orientational disorder. When compared with other bis-terpyridine complexes, this structure demonstrates that manganese(II) is no more prone to undergo low-symmetry distortions than systems with ligand field stabilization energy contributions.