Photophysical and Protonation Time Resolved Studies of Donor-Acceptor Branched Systems With Pyridine Acceptors.

A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues, by means of ambient and low temperature steady state spectroscopy and femtosecond to nanosecond time-resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors, and acetylene π-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed intramolecular charge transfer state on the picosecond time scale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Förster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral toward the protonated species on the 1 ps time scale is revealed.

Formation of a highly-ordered rigid multichromophoric 3D supramolecular network by combining ionic and coordination-driven self-assembly.

We present here the self-assembly of a green-emitting metallosupramolecular rhomboid into a rigid, highly-ordered 3D multichromophoric network through the mediation of a tetra-anionic violet-blue molecular emitter. Control was obtained on the spatial topology, the electronic energy landscape and the fluorescence polarization of the interacting dipoles.

Energy transfer within self-assembled cyclic multichromophoric arrays based on orthogonally arranged donor-acceptor building blocks.

We herein present the coordination-driven supramolecular synthesis and photophysics of a [4+4] and a [2+2] assembly, built up by alternately collocated donor-acceptor chromophoric building blocks based, respectively, on the boron dipyrromethane (Bodipy) and perylene bisimide dye (PBI). In these multichromophoric scaffolds, the intensely absorbing/emitting dipoles of the Bodipy subunit are, by construction, cyclically arranged at the corners and aligned perpendicular to the plane formed by the closed polygonal chain comprising the PBI units. Steady-state and fs time-resolved spectroscopy reveal the presence of efficient energy transfer from the vertices (Bodipys) to the edges (PBIs) of the polygons. Fast excitation energy hopping - leading to a rapid excited state equilibrium among the low energy perylene-bisimide chromophores - is revealed by fluorescence anisotropy decays. The dynamics of electronic excitation energy hopping between the PBI subunits was approximated on the basis of a theoretical model within the framework of Förster energy transfer theory. All energy-transfer processes are quantitatively describable with Förster theory. The influence of structural deformations and orientational fluctuations of the dipoles in certain kinetic schemes is discussed.

Significance of serum and bile tumor markers in the diagnostic approach of patients with malignant pancreatobiliary disease.

PURPOSE: Serum and bile tumor markers are under intense scrutiny for the diagnosis of malignant disease. The purpose of our study was to report the usefulness of serum and bile tumor markers for the discrimination between benign and malignant pancreatobiliary diseases. METHODS: Between March 2010 and May 2013, 95 patients with obstructive jaundice or history of biliary obstruction, were included in the study. During ERCP, bile samples were obtained for measurement of tumor markers CEA, CA19- 9, CA125, CA72-4 and CA242. Serum samples were taken before ERCP for the same measurements. The patients were divided into two groups: patients with malignant disease and patients with benign disease. RESULTS: Serum tumor marker levels were significantly higher in patients with malignant disease. Serum CA242 and CA19-9 exhibited the highest diagnostic accuracy (76.8% and 73.7%, respectively). CA125 and CA72-4 levels in bile samples were significantly higher in patients with malignant disease. Bile CA125, CEA and CA72-4 achieved the best diagnostic accuracy (69, 65 and 65), respectively). The combined detection of CA19-9, CA242 in serum and CA125, CA72-4 in bile along with total bilirubin levels, showed the best diagnostic accuracy (81%). CONCLUSIONS: Serum and bile tumor markers, when studied alone, lack the diagnostic yield to discriminate benign from malignant pancreatobiliary diseases. In cases of diagnostic dilemmas the combination of serum and bile markers might be helpful.

Highly efficient and unidirectional energy transfer within a tightly self-assembled host-guest multichromophoric array.

The coordination-driven synthesis of a rhomboid cavitand composed of two different Bodipys and its inclusion complex with 1,3,6,8-tetrasulfopyrene via ionic self-assembly was established by X-ray crystallography. Highly efficient and unidirectional intra-host and guest-to-host energy transfer was demonstrated by femtosecond fluorescence spectroscopy.

Synthesis, electrochemical and photophysical properties of covalently linked porphyrin-polyoxometalates.

Two covalently linked porphyrin-polyoxometalate hybrids have been prepared: an Anderson-type hexamolybdate [N(C(4)H(9))(4)](3)[MnMo(6)O(18){(OCH(2))(3)CNHCO(ZnTPP)}(2)] with two pendant zinc(II)-tetraphenylporphyrins, and a Dawson-type vanadotungstate [N(C(4)H(9))(4)](5)H[P(2)V(3)W(15)O(59){(OCH(2))(3)CNHCO(ZnTPP)}] with one porphyrin. Electrochemical studies show independent redox processes for the organic and inorganic parts at usual potentials. Photophysical studies reveal an electron transfer from the excited porphyrin to the Dawson polyoxometalate, but not to the Anderson polyoxometalate. Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants.

Efficient supramolecular synthesis of a robust circular light-harvesting Bodipy-dye based array.

We herein present the supramolecular construction of a completely fluorescent unquenched multichromophoric wheel consisting of boron dipyrromethene dyes arranged perpendicularly to the circular plane.

Controlling the stereospecificity of a volume-conserving adiabatic photoisomerization within a nanotubular self-assembled cage: a reversible light-heat torque converter.

We present herein a host-guest supramolecular system by which we were able to obtain precise control of the stereospecificity of a new and unusual adiabatic photoisomerization reaction capable of restoring reversibly the original configuration. The host-guest system is composed of (a) a naphthalene ring linked centrosymmetrically-via sp(2) hybridized oxygen atoms-with methoxytriethyleneglycol chains (1) and (b) a nanotubular cage formed by four self-assembled face-to-face ß-cyclodextrins threaded onto the long "axle" of 1. The compound 1 can exist in distinct cis,cis, cis,trans, and trans,trans conformations that are spectrally distinguishable (see Scheme 1 ). Spectroscopic and kinetic manifestations of the torsional isomerization of 1 in the lowest excited singlet state both in solution and within the tubular cage were investigated. The results provide clear evidence that the compact cavity completely blocks the photoisomerization pathway manifested in common solution (cis,cis* → cis,trans*), allowing observation of stereospecific, volume-conserving turning of the naphthalene ring about the two "quasidouble" bonds C(Naph)-O by φ ≈ 180° (cis,cis* → trans,trans*). The photoisomerization is purely adiabatic, and the encaged molecule restores its original configuration by generating torque thermally, when relaxing to the ground state.

Coordination-driven self assembly of a brilliantly fluorescent rhomboid cavitand composed of bodipy-dye subunits.

The two sp(3) hybridized fluorine atoms of a Bodipy dye have been synthetically replaced with the linear donor ligand 4-ethynylpyridine (-C≡C-Py) to form a rigid and highly symmetrical 109.5° building block in which the fluorophore subunit is vertically aligned to the plane formed by the -C≡C-Py donors. Upon reaction of the above tecton with a 90° organoplatinum acceptor unit, an intensely fluorescent rhomboid cavitand was manifested in solution. In contrast to the vast majority of coordination-driven self-assembled chromophoric systems, the present one fully conserves the excellent photophysical properties of the parent Bodipy dye. These unique features of the present metallosupramolecular entity constitute a fascinating metal-to-ligand self-assembled prototype for building compact and intensely luminescent materials with host-guest capabilities.

Free electron transfer with bifunctional donors: p-aminotritylsilanes.

This work provides an in-depth look at the bimolecular free-electron transfer (FET) from bisubstituted (amine and -CR(2)SiMe(3) groups) aromatic molecules to the solvent radical cations of n-BuCl. Because of the low rotational barriers, the substrates obtain all possible arrangements in solution. The electron jump is an unhindered process that does not require a defined encounter complex. The resulting radical cations show great conformer diversity because they directly inherit the geometry of their mobile precursors. One part of the radical cations is unstable and dissociates instantly, but the other one is metastable (microsecond lifetime). The two substituents reduce the barrier of internal rotation, resulting in stabilization of the otherwise good leaving group -SiMe(3). The amine group governs the reactivity of the system because it receives most of the electron density of the fluctuating highest MOs: primary and secondary amine groups lead to both instant and delayed formation of aminyl radicals; tertiary amines cause the rapid loss of an alpha-H(+) to yield alpha-aminoalkyl radicals.

Endoloop application as an alternative method for gastrotomy closure in experimental transgastric surgery.

BACKGROUND: Experimental studies investigating transgastric endoscopic surgery report closure of the gastric wall incision with clips. The author of this report describes endoloop placement as an alternative, equally efficient, faster method for gastrotomy closure. METHODS: Eight female pigs with a mean weight of 30 kg were used. Abdominal endoscopic exploration and transgastric operations including hepatic biopsies, bilateral tubal ligation, cholecystectomy, and closure of the gastrotomy were performed. The experiment was divided into two parts. The first part included five animals, which were killed immediately after the procedure. The second part included five animals, which were kept alive and killed 15 to 20 days later. RESULTS: The first part of the experiment, performed for technical skills acquisition, involved transgastric abdominal exploration, liver biopsies, and bilateral tubal ligation, which were successful for all five animals. The gastric wall incision was closed by applying clips in four animals and endoloops in one animal. During the autopsy at the end of the experiment, the sites of intervention were examined macroscopically. In the second part of the experiment, gastrotomy closure with endoloop application was performed in two animals and with clip application in one animal. All three animals survived, gained weight, and demonstrated no signs of infection. They were killed 15 to 20 days after the procedure, and no signs of intraabdominal infection were found. Cultures from the peritoneal cavity were negative. At necropsy, macroscopic and microscopic examination confirmed complete healing of the gastrotomy. CONCLUSIONS: Transgastric endoscopic surgery is technically feasible and effective. The application of endoloops for closure of the gastric opening is a fast, easy, and equally safe alternative to clip placement.

Ionization of aromatic sulfides in nonpolar media: free vs reaction-controlled electron transfer.

The primary products of the bimolecular free electron transfer (FET) from aromatic sulfides (PhSCH2Ph, PhSCHPh2, PhSCPh3) to n-butyl chloride radical cations are two radical cation conformers: a dissociative and a metastable one. In analogy with formerly studied donor systems, this result seems to reflect femtosecond oscillations in the ground state of the sulfides such as torsion motions around the Ar-S bond. This motion is accompanied by a marked electron fluctuation within the HOMO (or the n) orbitals. The FET products observed in the nanosecond time scale such as the metastable sulfide radical cations (Ar-S-CR3*+), the dissociation products R3C+; and R3C*, and their (experimentally) nondetectable counterparts Ar-S* as well as Ar-S+ can be understood with the simplified assumption of two extreme conformations, namely a planar and a twisted donor molecule. Using mediator radical cations (benzene, butylbenzene, biphenyl), the stepwise reduction of the free energy of the electron transfer from -DeltaH = 2.5 to

Free electron transfer from xanthenyl- and fluorenylsilanes (Me3 or Ph3) to parent solvent radical cations: effects of molecule dynamics.

Parent radical cations of nonpolar solvents (alkanes and alkyl chlorides) ionize 9-(trimethylsilyl)xanthenes and 9-(trimethylsilyl)fluorenes in a diffusion-controlled electron transfer. The actual electron jump as the deciding part of the process does not require a defined encounter complex, and therefore the reactants are not subjected to any geometry optimization. Considering the molecule dynamics of the donors, bending motions of the silyl group are concerted with fluctuations of the highest occupied molecular orbital electrons. Ionizing such a standing conformer mixture creates metastable (microsecond) as well as dissociative donor radical cations. A mobility restriction of the benzylic silane group in positions vertical to the phenyl plane stabilizes the radical cations and accounts for a declining amount of dissociative radical cations, which undergo C-Si bond fragmentation in the order benzylsilane > xanthenylsilane > fluorenylsilane.