Synthesis,structural analysis,and self-assembly of phenylene ethynylene oligomers and their ?F, ?CF3, and ?CH3 substituted derivatives

Oligomers consisting of aromatic building blocks separated by alkynyl units were synthesized by Sonogashira cross-coupling of aryl halides with terminal acetylenes. Strong electron acceptors such as  F and  CF₃ and weak electron donors like  CH₃ were placed as substituents on one of the benzene rings. Acetyl-protected sulfhydryl groups were attached to one end of these molecules to promote their self-organization on gold surfaces. The electron-transport properties of such self-assembled monolayers (SAMs) are highly sensitive to the local order of the molecules in the solid state. Single crystals were analyzed by X-ray diffraction experiments that revealed structural details that could lead to a better understanding of the electron-transport properties. The unsymmetrical substitution of the aromatic rings by electron-active groups in the ortho-, meta-, or para positions resulted in changes of such molecular parameters as bonding and torsion angles and planarity. These parameters, in turn, can affect the angle of the molecular attachment to a gold substrate and the density of the resulting SAMs. Patterned SAMs of some of these molecules and comparison alkane thiols were obtained on gold by microcontact printing or flooding. The SAM thickness was determined by spectroscopic ellipsometry. Surface potential differences between adjacent SAMs or between SAMs and the gold substrate were measured by scanning surface potential microscopy under ambient conditions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 541–550, 2004     

Wavelength-Resolved 3-Dimensional Fluorescence Lifetime Imaging

We have developed a compact system for wide-field fluorescence imaging, resolved in three spatial dimensions, lifetime and wavelength, that is based on a gated optical intensifier and an all-solid-state diode pumped Cr:LiSAF oscillator-amplifier system. Exploiting spectral separation, the system has been applied to human teeth, obtaining good lifetime contrast between enamel, dentin and caries. Exploiting spectral separation combined with depth resolution, the study of fluorescent microspheres led to an enhancement in both lifetime contrast and lateral resolution.     

E2 polynomial strengths: A comparison with shell-model results

Polynomial-expansion E2 strengths and sum rules involving (J,T)=(0, 0)and(2, 0) states of (ds)⁶ are compared with shell-model results. The agreement is excellent. The strength distribution is describable as a narrow linear ridge in the energy space. The level-to-level fluctuations in the total strength are small, as expected from a theorem of Dyson and Mehta; fluctuations in the first and second moments are also small. The effect of collectivity and the partitioning of the sum rules into exothermic and endothermic parts are discussed.     

Spectral averaging for single-nucleon-transfer sum rules

Spectral averaging methods are used to calculate, directly in terms of the Hamiltonian matrix elements, the quantities determined by the non-energy-weighted and linear-energy-weighted sum rules for single-nucleon addition and removal. Occupancies and strength centroids, and their isospin decomposition, are given throughout the spectrum for some ds-shell cases.     

Isolation and Structure of a New Antibiotic Related to Rubiflavin A

A novel antibiotic, PD 121,222, was isolated from a complex of pluramycin-like compounds containing mostly kidamycin and neopluramycin. Spectral analyses showed that this compound is the 14,16-dihydroxy analog of rubiflavin A.