The effect of a mild base on curcumin in methanol and ethanol

Steady-state and time-resolved emission techniques were employed to study the effect of acetate, a mild base, on the luminescence of curcumin in methanol and ethanol. We found that the steady-state emission intensity as well as the average fluorescence decay time are reduced by a factor of 5 when the acetate concentration is raised to about 1.8 M. We attribute this large effect to an excited-state proton transfer (ESPT) from the acidic groups of curcumin to the acetate anion. We analyze the experimental data in terms of an ESPT reaction occurring between a photoacid and a base.     

Pair-density-wave correlations in the Kondo-Heisenberg model

We show, using density-matrix renormalization-group calculations complemented by field-theoretic arguments, that the spin-gapped phase of the one dimensional Kondo-Heisenberg model exhibits quasi-long-range superconducting correlations only at a nonzero momentum. The local correlations in this phase resemble those of the pair-density-wave state which was recently proposed to describe the phenomenology of the striped ordered high-temperature superconductor La(2-x)Ba(x)CuO?, in which the spin, charge, and superconducting orders are strongly intertwined.     

Control of temperature and entropy by frequent quantum measurements

We study deviations from thermal equilibrium between two-level systems (TLS) and a bath by frequent and brief quantum measurements of the TLS energy-states. The resulting entropy and temperature of both the system and the bath are found to be completely determined by the measurement rate, and unrelated to what is expected by standard thermodynamical rules that hold for Markovian baths. These anomalies allow for very fast control heating, cooling and state-purification (entropy reduction) of quantum systems much sooner than their thermal equilibration time.     

On Homogeneous Standard Integral Table Algebras of Degree 4

In this paper we classify, up to exact isomorphism, the algebras in the title which contain a faithful element and in which every non-trivial table subset has dimension at least five.     

Temperature dependence of the fluorescence properties of thioflavin-T in propanol, a glass-forming liquid

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of Thioflavin-T (ThT) in 1-propanol as a function of temperature. We found that the nonradiative rate, k(nr), decreased by about 3 orders of magnitude when the temperature was lowered to 88 K. We found remarkably good correspondence between the temperature dependence of k(nr) of ThT and the dielectric relaxation times of the 1-propanol solvent.     

Polychromatic vectorial vortex formed by geometric phase elements

We propose the use of a geometric phase, obtained by spatial polarization state manipulations, for the formation of polychromatic vectorial vortices. Experimental demonstration is obtained by using Pancharatnam-Berry phase optical elements formed by a space-variant subwavelength grating etched on a GaAs wafer. We further demonstrate formation of scalar and unpolarized polychromatic vortices.     

A Bessel identity for the theta correspondence

We establish a spectral identity between global Bessel distributions with respect to generic cuspidal representations of an odd orthogonal group and the metaplectic cover of a symplectic group which are related by the theta correspondence. We also provide analogous local identities for square-integrable representations.     

Kinetic investigation of the upper laser levels of the copper vapor laser

A modernized hook apparatus was used to study the population history of the ²P_{$\text{1}\text{2}$} and ²P_{$\text{3}\text{2}$} upper laser levels of the copper vapor laser. It was found that the effective lifetime of these levels is a sensitive function of the laser input current. The population of these levels saturates for a peak current of 200 A, which corresponds to a voltage slightly above the breakdown voltage of the tube.     

Collinear nondegenerate four-wave mixing by a three-level system

Four-wave mixing in the vicinity of a sodium doublet is reported. The three-level system allows collinear phase-matching. The FWM is resonantly enhanced by a high gain on the blue side of the D₁ transition.Present address: LROL, Physics Department, Laval University, Quebec, Canada, G1K 7P4To whom correspondence should be addressed     

The impact of solvent polarity on intramolecular proton and electron transfer in 2-alkylamino-4-nitro-5-methyl pyridine N-oxides

The crystal structure of 2-butylamino-4-nitro-5-methyl pyridine N-oxide (2B5M) and solution studies of both 2B5M and 2-methylamino-4-nitro-5-methyl pyridine (2M5M) N-oxide are presented. Steady-state absorption and emission measurements were employed for both molecules while a picosecond fluorescence up-conversion technique was used to follow the dynamic behavior of the 2M5M system. The experimental methods were complemented by DFT and TD DFT B3LYP/6-31G(d,p) calculations involving ground and excited-state optimization which in the case of the smaller 2M5M molecule were extended to the CAM-B3LYP/6-31G(d,p) method. The solvent effect is incorporated by applying the polarizable continuum (PCM) model. The data reveal that the 2B5M molecule crystallizes in the monoclinic space group P2(1)/c and its crystal lattice is composed of monomers with intramolecular N-H···O [2.572(3) ?] hydrogen bonds, connected into a polymer network by weak intermolecular C-H…O [3.2-3.4 ?]-type interactions. Quantum-chemical calculations show that the aminoalkyl substitutent in aminoalkyl-pyridine N-oxides is a specific determinant of the CT nature of the lowest-lying excited electronic ππ* state, distinguishing them from other nitroaromatic compounds. The results of both picosecond fluorescence up-conversion experiments in different solvents and quantum-chemical calculations suggest that in nonpolar media the ESIPT process in 2M5M is favored, while in polar acetonitrile, the N* → PT* transition demands barrier-crossing and thus unfavorable thermodynamic conditions do not allow the ESIPT to occur. The signals of picosecond fluorescence up-conversion of 2M5M are solvent- and emission-wavelength dependent. The three time components found in a weakly polar isooctane-dioxane mixture have been attributed to solvation dynamics (～500 fs), and to relaxation of N* and PT* forms while in acetonitrile, a very rapid fluorescence decay with a time constant (2.3-4.0 ps) indicative of the presence of the normal (N*) form was observed. Much shorter fluorescence lifetimes in alcohols (a few picoseconds) and in D(2)O (less than 200 fs) than in aprotic solvents suggest that in protic media, the solvent molecules participate in the ESIPT, bridging between the methylamine group and the N-oxide group of 2M5M.