Construction of a wheat-flour state diagram

We use pressure-variable differential scanning calorimetry to detect and characterize thermally induced transitions (glass, melting, gelatinization) in pre- and post-extruded wheat flour. The resulting data allow us to construct a two-dimensional state diagram which maps the physical states that pre- and post-extruded wheat flour can assume, at constant pressure, as a function of moisture content, temperature, and the specific mechanical energy, SME, generated in the extruder. We describe how this state diagram can be used to map the path of extrusion processing, to assess the impact of extrusion conditions, and, ultimately, to design formulations and processing conditions that result in desired end-product attributes. For the extrudates, we find that the extent of processing-induced fragmentation, as monitored by reductions in the extrudate glass transition temperature,T _g, increases with the SME generated in the extruder. We demonstrate that a wheat-flour state diagram, which includes the glass curve of the wheat-flour extrudates produced at various SME values, allows one to predict and control the impact of processing conditions on extrudate properties.     

Pseudopure state of a twelve-spin system

Pseudopure states of a system of twelve interacting spins are experimentally demonstrated. The system is a cluster of dipolar-coupled nuclear spins of fully labeled (13)C(6)-benzene in a liquid crystalline matrix. At present, this is the largest and the most complex composite system where individual quantum states have been addressed.     

A neutral state green polymer with a superior transmissive light blue oxidized state

This report highlights the synthesis of only the second green polymer in the literature, which possesses superior properties over the first: a highly transmissive light blue color in the oxidized state with high optical contrast and excellent switching properties.     

Rigid cage conversion of a perfluoroalkyl iodide repulsive electronic state into a “bound” electronic state

260–300 nm pulsed “photodissociation” of perfluoroalkyl iodide guests in rare gas and N₂ lattices produces an unstructured structured 850–1050 nm emission. The excitation spectrum is continuous, and the emission maximum and lifetime vary from host to host. It is proposed that this emission occurs from a vibrationally relaxed, stationary “bound” electronic state in which the perfluoroalkyl radical and the I^*(²P_{$\text{1}\text{2}$}) atom are held together by constrictive cage forces.     

Thermal properties of a molecule in a constrained state

The thermal properties of a dye molecule (guest) inside the cavity of a host amylose helix were studied by TGA, DSC, and Thermal Desorption MS. The results show that the degradation temperature of dye shifts to a higher temperature by approximately 20°C.     

Observation of a metastable 2a state in BaCl

Laser-induced fluorescence of gaseous BaCl was studied in the 0.5-2.0 μm spectral region. Transitions to a metastable ²Δ electronic state were observed which made a rotational and vibrational analysis possible of the Ω = 5/2 componet of this state.     

Is tetramethyleneethane a ground state triplet?

We have examined a number of possible ways by which tetramethyleneethane (TME) can be a ground state triplet, as claimed by experimental studies, in violation of Ovchinnikov’s theorem for alternant hydrocarbons of equal bond lengths. Model exact π calculations of the low-lying states of TME, 3,4-dimethylenefuran and 3,4-dimethylenepyrrole were carried out using a diagrammatic valence bond approach. The calculations failed to yield a triplet ground state even after (a) tuning of electron correlation, (b) breaking alternancy symmetry, and (c) allowing for geometric distortions. In contrast to earlier studies of fine structure constants in other conjugated systems, the computedD andE values of all the low-lying triplet states of TME for various geometries are at least an order of magnitude different from the experimentally reported values. Incorporation of σ-π mixing by means of UHF MNDO calculations is found to favour a singlet ground state even further. A reinterpretation of the experimental results of TME is therefore suggested to resolve the conflict.     

Multiple spin-echoes in a photo-excited triplet state

A Carr-Purcell multiple spin-echo, as modified by Meiboom and Gill, is described for the 3598 MHz zero-field transition of phosphorescent quinoline C₉ND₇ in a durene host. The results show that the dephasing of the electron spins through spectral diffusion may be largely eliminated by the multiple echo technique.     

Excited state characterization of a polymeric indigo

A comprehensive investigation of the solution photophysics of a 5,5'-methylene-bridged polymeric indigo, a statistical copolymer consisting of indigo and N-acetylindigo units, was performed in organic solvents at room temperature and further compared with indigo. A complete spectral and photophysical characterization based on photoacoustic calorimetry, steady-state and time-resolved fluorescence data was undertaken. A fluorescence quantum yield of 0.00037 and an intersystem crossing singlet-to-triplet quantum yield of 0.006 (close to the value for indigo) were obtained, leading to a value of 0.9936 for the S(1) → S(0) internal conversion (IC) quantum yield. Spectral and photophysical characteristics similar to indigo were obtained with, however, a special signature: it (mainly) decays single exponentially (in contrast with indigo, found to decay bi-exponentially), with a decay time value of 40-50 ps and an even more efficient S(1) → S(0) IC deactivation channel, related to an efficient energy migration within an energetic ladder of the polymer chromophoric segments. The photochemistry of this polymer, namely the degradation under light excitation, was also investigated and the obtained photoreaction quantum yield (?(R)) in DMF was found to be 0.003, which is lower than the previously determined value for indigo in the same solvent (?(R) = 0.0078). The overall data indicate that although the polymer and indigo have a close finger-print, the former is more stable which is suggested to be due to the additional intramolecular energy transfer process (within different chromophoric units) found with the polymer.     

Synthesis of a novel diarylphosphinic acid: a distorted ground state mimic and transition state analogue for amide hydrolysis

We describe herein the synthesis of a new unsymmetrical diarylphosphinic acid, a hapten aimed to produce catalytic antibodies for the hydrolysis of heterocyclic amides. The phosphinate functionality was selected as a mimic both of the tetrahedral intermediate and the transition state of higher energy along the reaction profile. The phenyl and 2,4,6-(trimethyl)-phenyl groups flanking the phosphinate were chosen in order to impose rotation around the P–C bond, a choice supported by ab initio calculations. This new hapten should elicit catalytic antibodies whose binding site could affect the distortion at nitrogen as well as the twist along the N–C(O) bond for heterocyclic amides. This hapten along with a series of new sterically hindered unsymmetrical phosphinic acid derivatives was prepared by a key palladium-catalysed step.     

Shedding light on a dark state: the energetically lowest quintet state of C2

In this work we present a deperturbation study of the d?(3)Π(g), v=6 state of C(2) by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system (d(3)Π(g)-a?(3)Π(u)) unveils the presence of the energetically lowest high-spin state of C(2) in the vicinity of the d?(3)Π(g), v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the 1?(5)Π(g) state at rotational quantum numbers N ≤ 11. The spectral complexity for transitions to the v = 6 level of d?(3)Π(g) state is further enhanced by an additional perturbation at N = 19 and 21 owing to the b?(3)Σ(g)(-), v=19 state. The spectroscopic characterization of both dark states is accessible by the measurement of 122 "window" levels. A global fit of the positions to a conventional Hamiltonian for a linear diatomic molecule yields accurate molecular constants for the quintet and triplet perturber states for the first time. In addition, parameters for the spin-orbit and L-uncoupling interaction between the electronic levels are determined. The detailed deperturbation study unravels major issues of the so-called high-pressure bands of C(2). The anomalous nonthermal emission initially observed by Fowler in 1910 [Mon. Not. R. Astron. Soc. 70, 484 (1910)] and later observed in numerous experimental environments are rationalized by taking into account "gateway" states, i.e., rotational levels of the d?(3)Π(g), v=6 state that exhibit significant (5)Π(g) character through which all population flows from one electronic state to the other.     

Ultrafast excited state relaxation dynamics of branched donor-pi-acceptor chromophore: evidence of a charge-delocalized state

Excited-state dynamics and complete transient absorption features of the trimer tris-4,4',4' '-(4-nitrophenyleethynyl)triphenylamine and the monomer 4-N,N-(dimethylamino)-4'-nitrotolane have been obtained from femtosecond pump-probe spectroscopy. The measurements are carried out to understand the mechanism behind enhanced two-photon absorption cross-sections of branched systems over their linear counterparts. Absorption and emission transition dipole moments of monomer and trimer in toluene have suggested that the emitting state of trimer is different from the monomer and probably is arising from the charge-delocalized C(3) symmetry state. Ultrafast transient absorption measurements on these molecules have spectroscopically validated the presence of an initial electron delocalized state with the C(3) symmetry state in the trimer molecule. The results have shown that there is a slower rate of internal conversion from the C(3) symmetry state to intramolecular charge transfer of trimer suggesting a barrier between them. Also, presence of a charge-stabilized state and involvement of a nonemissive state in the excited-state deactivation has been observed for both monomer and trimer.     

Radical cation of a trimethylenemethane with a nondegenerate ground state

Upon ionization by gamma-irradiation in frozen CFCl(3), or by X-irradiation in an Ar matrix, 2,2,3,3-tetramethylmethylenecyclopropane (MCP-Me4) readily undergoes ring opening to yield the radical cation of 1,1,2,2-tetramethyltrimethylenemethane (TMM-Me4). The hyperfine-coupling constants for TMM-Me4(.+) are (mT) -1.99 (2H), +0.53 (6H), and +0.19 (6H), and the singly occupied orbital closely resembles one of the two degenerate nonbonding pi-MOs (NBMOs) of trimethylenemethane (TMM). Due to the expected effect of the methyl substituents, this "symmetric" NBMO, psi(2+) (b(1)), is energetically favored relative to its "antisymmetric" counterpart, psi(2-) (a(2)), so that the ground state assumes a structure with (2)B(1) symmetry in the C(2v) point group. Calculations show that the ring opening in the primary radical cation MCP-Me4(.+) to yield TMM-Me4(.+) is spontaneous, whereas in the parent system (MCP(.+) --> TMM(.+) a low barrier does exist. In contrast to the previously investigated case of the radical cation of tetramethyleneethane, the "electromer" of TMM-Me4(.+), in which the unpaired electron occupies psi(2-), cannot be attained photochemically.