Implementation of recycling routes for scanning probe microscopy tips.

In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route.     

Determination and characterization of a transition structure for water–formaldehyde addition

Quantum mechanical calculations of the geometric, energetic, electronic, and vibrational features of a transition structure for gas-phase water–formaldehyde addition (FW1?) are described, and a new transition-structure search algorithm is presented. Basis-set-dependent effects are assessed by comparisons of computed properties obtained from self-consistent field (SCF) molecular orbital (MO) calculations with STO-3G, 4-31G, and 6-31G^** basis sets in the absence of electron correlation. The results obtained suggest that STO-3G-level calculations may be sufficiently reliable for the prediction of the transition structure of FW1? and for the transition structures of related carbonyl addition reactions. Moreover, the calculated activation energy for formation of FW1? from water and formaldehyde (?44 kcal mol^?1) is very similar in all three basis sets. However, the energy of formaldehyde hydration predicted by STO-3G (? ?45 kcal mol^?1) is about three times larger than that predicted by the other two basis sets, with the activation energy for dihydroxymethane dehydration also being too large in STO-3G. Calculated force constants in all three basis sets are generally too large, leading to vibrational frequencies that are also too large. However, uniformly scaled force constants (in internal coordinates) give much better agreement with experimental frequencies, scaled 4-31G force constants being slightly superior to scaled STO-3G force constants.     

Ranking Oxidant Sensitiveness: A Guide for Synthetic Utility

Common oxidants used in chemical synthesis, including newly developed perruthenates, were evaluated in the context of understanding (and better appreciating) the sensitiveness and associated potential hazards of these reagents. Analysis using sealed cell differential scanning calorimetry (scDSC) facilitated Yoshida correlations, which were compared to impact sensitiveness and electrostatic discharge experiments (ESD), that enabled sensitiveness ranking. Methyltriphenylphoshonium perruthenate (MTP3, 8 ), isoamyltriphenylphosphonium perruthenate (ATP3, 7 ) and tetraphenylphosphonium perruthenate (TP3, 9 ) were found to be the most sensitive followed by 2-iodoxybenzoic acid (IBX, 2 ) and benzoyl peroxide (BPO, 10 ), whereas the most benign were observed to be Oxone ( 12 ), manganese dioxide (MnO₂, 13 ), and N-bromosuccinimide (NBS, 17 ).     

Dendrimer molecules with record large two-photon absorption cross section

We report what is to our knowledge a record high value for an intrinsic two-photon absorption (TPA) cross section, sigma(2) = 11 x 10(-47)> cm>(4)> s photon(-1) molecule(-1), measured with femtosecond pulses in a new dendrimer molecule comprising 29 repeat units of 4, 4(?)-bis(diphenylamino)stilbene chromophore. We measure the dependence of TPA on excitation wavelength in three consecutive generations of the dendrimer and show that the maximum sigma(2) value increases faster than the total number of stilbene chromophores. This result indicates that it is possible to obtain even larger sigma(2) values in higher generations of this dendrimer family.     

Elastic and inelastic electron tunneling spectroscopy of a new rectifying monolayer

Rectification of electrical current was observed in a Langmuir-Schaefer monolayer of fullerene-bis[ethylthio-tetrakis(3,4-dibutyl-2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate, Au electrodes at room temperature (there are two regimes of asymmetry, at lower bias, i.e., between 0 and +/-2 V, and at higher bias), and also between Pb and Al electrodes at 4.2 K. The latter experiment was coupled with second harmonic detection of the second derivative of the current with respect to voltage (d2I/dV2). The d2I/dV2 spectrum shows intramolecular vibrations, and also two antisymmetric broad bands, centered at +/-0.65 V, due to resonant electron tunneling between the Fermi level(s) of the electrodes and the lowest unoccupied molecular orbital of the molecule.     

Investigation of solvatochromism in the low-lying singlet states of dithienyl polyenes

To understand the low-lying singlet states of dithienyl polyenes, we investigated the solvatochromism of a series of α,ω-di(2-dithienyl 3,4-butyl) polyenes having n=1–5 double bonds. Absorption and emission spectra were collected in a series of aprotic solvents. The absorption energy dispersion effect sensitivity increased smoothly with n, reaching asymptotic behavior as n approached 5. The emission energy had less solvent sensitivity. The trends gave evidence for the existence of a ¹B^*_u absorbing state and a ¹A^*_g emitting state. We observed sensitivity of the absorbing and emitting states to solute–solvent electrostatic interactions, suggesting the dithienyl polyenes had a polar ground state conformation.