Three-photon excitation ofp-quaterphenyl with a mode-locked femtosecond Ti:sapphire laser

We observed emission fromp-quaterphenyl (p-QT) at 360 nm when exposed to the focused light from a femtosecond (fs) Ti:sapphire laser at 850 nm. This wavelength is too long to allow two-photon excitation of p-QT. The emission intensity of p-QT was found to depend on the cube of the laser power at 850 nm, suggesting that excitation occurs due to a three-photon process. The same emission spectrum and single exponential decay times were observed for three-photon excitation at 850 nm as for two-photon excitation at 586 nm and for one-photon excitation at 283 nm. The same rotational correlation times were observed for one-, two-, and three-photon excitation, but higher time-zero anisotropies were observed for two- and three-photon excitation. The steady-state anisotropies for one-, two-, and three-photon excitation are precisely consistent with cos², cos⁴, and cos⁶ excitation photoselection, where is the angle between the electric field of the incident light and the absorption dipole. These experiments were performed with 3×10^–5 M solutions of p-QT. Use of such low concentrations was possible because p-QT displays one of the highest apparent cross sections we have observed to date for three-photon excitation. The spatial distribution of the excited fluorescence was less for three-photon excitation than for two-photon excitation of Coumarin 102 at the same 850-nm excitation wavelength. The high cross section, photostability, and clear cos⁶ photoselection of p-QT make it an ideal three-photon standard for spectroscopy and microscopy.     

A theoretical study of the structural,thermoelectric, and spin-orbit coupling influenced optoelectronic properties of CsTmCl3 halide perovskite

This first principles study explores the structural, electronic, optical, and thermoelectric properties of the CsTmCl₃ halide perovskite using density functional theory. The structural and thermoelectric properties are calculated without considering the spin-orbit coupling (SOC), while both the electronic and optical properties are calculated with and without the SOC effect. A comparison of the results obtained with and without SOC reveals that inclusion of the SOC effect reduces the band gap from 1.18 to 0.99 eV due to shifting of the Tm-d states toward the Fermi level. However, direct nature of the band gap remains the same in both the cases. The effect of SOC on the optical properties is, however, only visible in shifting of the third characteristic peak to lower energies. Strong optical absorption in the visible and ultraviolet regions shows effectiveness of CsTmCl₃ in the optical devices working in these regions. Moreover, the calculated transport properties reveal CsTmCl₃ as a useful thermoelectric material at room temperature.     

Cu(I)-anchored polyvinyl alcohol coated-magnetic nanoparticles as heterogeneous nanocatalyst in Ullmann-type C–N coupling reactions

In this paper, the preparation of a novel magnetic nanocatalyst (Fe₃O₄@PVA/CuCl) is described, which involves coating of polyvinyl alcohol (PVA) onto the surface of Fe₃O₄ nanoparticles and its subsequent coordination with CuCl catalyst. The nanocatalyst was characterized by various analytical methods, including Fourier-transform infrared, X-ray diffraction, inductively coupled plasma spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy, vibrating-sample magnetometry, and EDX elemental mapping. Moreover, the nanocatalyst was efficiently used in the N-arylation of amines via the formation of a carbon–nitrogen bond between the aryl halides and amines by Ullmann-type coupling reactions. The catalyst was sufficiently stable and can be reused for at least seven times in a model Ullmann reaction without remarkable alteration in its catalytic behavior. Heterogeneity of the catalyst was investigated by a hot filtration test.     

Fluorescence of horse liver alcohol dehydrogenase using one- and two-photon excitation

We examined the steady-state and time-resolved emission of liver alcohol dehydrogenase resulting from one-photon and two-photon excitation. Previous studies with one-photon excitation revealed that the two nonidentical tryptophan residues display different emission spectra and decay times. The use of two-photon excitation resulted in similar emission spectra, multiexponential intensity decays, time-resolved emission spectra, and anisotropy decays as was observed for one-photon excitation. These results suggest that both nonidentical tryptophan residues are excited to a similar extent for one- and two-photon excitation. However, the limiting anisotropy (r ₀) with two-photon excitation from 585 to 610 nm is below 0.1 and appears distinct from that observed previously forN-acetyl-l-tryptophanamide.Abbreviations LADH liver alcohol dehydrogenase - -NAD⁺ -nicotinamide adenine dinucleotide - OPE one-photon excitation - OPIF one-photon induced fluorescence - TPE two-photon excitation - TCSPC time-correlated single photon counting - TPIF two-photon induced fluorescence     

(±)‐3‐Oxocyclo­pentanecarboxylic acid: the smallest keto acid known to aggregate by catemeric hydrogen bonding

The title compound, C₆H₈O₃, is the smallest keto acid yet found to aggregate in the solid as acid‐to‐ketone hydrogen‐bonded catemers. Four translational chains pass through the cell in the a direction [O⋯O = 2.6915 (14) Å and O—H⋯O = 166°]. Two inter­molecular C—H⋯O close contacts exist, involving both carbonyl functions.     

Functionalization of multi‐walled carbon nanotubes by the baclofen drug to immobilize palladium nanoparticles and catalyze Sonogashira coupling reactions

The baclofen‐MWCNTs‐Pd nanocatalyst was synthesized through covalent grafting of baclofen molecules onto surface‐modified carbon nanotubes and immobilizing Pd nanoparticles by the baclofen ligands. The chemical structure of the produced nanocatalyst was studied by Raman spectroscopy, Fourier transform‐infrared spectroscopy, energy‐dispersive spectroscopy (EDS), elemental mapping and inductively coupled plasma analysis. Also, its surface morphology was determined using the scanning and transmission electron microscopy techniques. Furthermore, the obtained baclofen‐MWCNTs‐Pd nanocatalyst is demonstrated to exhibit very high activity as a heterogeneous phosphine‐free catalyst in Sonogashira cross‐coupling of aryl halides by giving good to excellent yields of different products. In addition, the nanocatalyst can be reused four times without any significant leaching or loss of activity.     

Crafting Core/Graded Shell–Shell Quantum Dots with Suppressed Re‐absorption and Tunable Stokes Shift as High Optical Gain Materials

The key to utilizing quantum dots (QDs) as lasing media is to effectively reduce non‐radiative processes, such as Auger recombination and surface trapping. A robust strategy to craft a set of CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS core/graded shell–shell QDs with suppressed re‐absorption, reduced Auger recombination rate, and tunable Stokes shift is presented. In sharp contrast to conventional CdSe/ZnS QDs, which have a large energy level mismatch between CdSe and ZnS and thus show strong re‐absorption and a constrained Stokes shift, the as‐synthesized CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS QDs exhibited the suppressed re‐absorption of CdSe core and tunable Stokes shift as a direct consequence of the delocalization of the electron wavefunction over the entire QD. Such Stokes shift‐engineered QDs with suppressed re‐absorption may represent an important class of building blocks for use in lasers, light emitting diodes, solar concentrators, and parity‐time symmetry materials and devices.