Novel phosphate halides BaMnIII[PO4]FCl and BaMnIII[PO4]F2: Effects of mixed halides on crystal structures and magnetic properties

The objective of this research program has been to explore the equilibrium and non-equilibrium dynamical properties of ReO/sub 4//sup -/ molecules embedded in alkali halide lattices using electromagnetic radiation. Both incoherent sources and CO/sub 2/ laser radiation have been used to explore the full dynamic range of the molecular vibrational modes. To achieve this objective stable molecular dopant - alkali halide combinations have been fabricated which have vibrational modes near the CO/sub 2/ laser frequencies. In order to uncouple the molecular modes from the lattice modes, to simplify the analysis as much as possible, low temperature spectroscopic measurements were required. In general, it was found that the molecular vibrational modes in the low temperature quiescent lattice had extremely narrow linewidths (less than 0.1 cm/sup -1/) so that most of the coincidences with the CO/sub 2/ laser lines were eliminated.

In this chapter, I discuss the application of two-dimensional infrared (2D IR) spectroscopy to understand the ultrafast dynamics of molecular vibrational polaritons. When molecular vibrational modes and photon cavity modes strongly couple to each other, they form hybridized quasiparticles, the so-called molecular vibrational polaritons. Polaritons thereby possess half-photon half-matter characters, which render them to inherit characters from both sides, e.g., lead to modified chemical reactions. It is pertinent to understand the ultrafast molecular dynamics of polaritons, in order to rationally design polariton-modified reactions. The intrinsic timescale of molecular vibrational and cavity modes makes polaritons evolve in ultrafast timescales, e.g. polaritons relax to dark modes in a few picosecond. Therefore, femtosecond vibrational spectroscopy is ideal to follow such dynamics. In this chapter, I provide an overview of femtosecond 2D IR spectroscopic studies from my group. I will first introduce the spectral interpretation. Then, I will show that the dynamics of molecular vibrational polaritons are different from the ones of their molecular counterparts, such as hot vibrational dynamics and intermolecular vibrational energy transfer. These distinct dynamics can serve as the foundation for further design of polariton-modified reactions.

Thermochromatium tepidum is a thermophilic purple sulfur photosynthetic bacterium collected from the Mammoth Hot Springs, Yellowstone National Park. A previous study showed that the light-harvesting-reaction center core complex (LH1-RC) purified from this bacterium is highly stable at room temperature (Suzuki, H., Hirano, Y., Kimura, Y., Takaichi, S., Kobayashi, M., Miki, K., and Wang, Z.-Y. (2007) Biochim. Biophys. Acta 1767, 1057-1063). In this work, we demonstrate that thermal stability of the Tch. tepidum LH1-RC is much higher than that of its mesophilic counterparts, and the enhanced thermal stability requires Ca2+ as a cofactor. Removal of the Ca2+ from Tch. tepidum LH1-RC resulted in a complex with the same degree of thermal stability as that of the LH1-RCs purified from mesophilic bacteria. The enhanced thermal stability can be restored by addition of Ca2+ to the Ca2+-depleted LH1-RC, and this process is fully reversible. Interchange of the thermal stability between the two forms is accompanied by a shift of the LH1 Qy transition between 915 nm for the native and 880 nm for the Ca2+-depleted LH1-RC. Differential scanning calorimetry measurements reveal that degradation temperature of the native LH1-RC is 15 degrees C higher and the enthalpy change is about 28% larger than the Ca2+-depleted LH1-RC. Substitution of the Ca2+ with other metal cations caused a decrease in thermal stability of an extent depending on the properties of the cations. These results indicate that Ca2+ ions play a dual role in stabilizing the structure of the pigment-membrane protein complex and in altering its spectroscopic properties, and hence provide insight into the adaptive strategy of this photosynthetic organism to survive in extreme environments using natural resources.

We present a comprehensive approach for tailoring the spectral and angular properties of infrared thermal radiation by using a polymer resonator with molecular vibrational modes, consisting of a polymer thin film on a back-reflective substrate. To precisely design the resonator, we derived the infrared dielectric function of a poly(methyl methacrylate) (PMMA) thin film from the measured reflectance spectrum by fitting it with a Gaussian-convoluted Drude-Lorentz model while accounting for the inhomogeneous broadening caused by the disordered structure of polymers. Our experimental and numerical characterization confirms that the polymer resonator exhibits spectral shaping from quasi-broadband to narrowband due to the intrinsic molecular vibrational absorption of the polymer. The frequency-isolated and strong molecular vibrational absorption of the carbonyl stretching mode at 1730 cm-1 enables the narrowband shaping of the PMMA resonator. In addition, we confirm that the angular-shaping characteristics of this polymer resonator can be tuned, from omnidirectional to strongly angular selective, by changing its polymer film thickness. Modal dispersion analysis reveals that the angle-selectivity of the polymer resonator at an angle of incidence of 80° comes from coupling between the molecular vibrational mode and leaky mode. The proposed infrared radiation management strategy based on molecular vibrational modes of polymers is cost-effective, scalable, and works well with terrestrial matter, including organic compounds and gas molecules, showing promise for applications such as optical gas sensing and radiative thermal management.

The effect of different siloxane chain-extenders on the thermal degradation and stability of segmented polyurethanes

Generation and control of entanglement and arbitrary superposition states in molecular vibrational and rotational modes by using sequential chirped pulses

Factor Group Analysis of Molecular Vibrational Modes of Graphene and Density Functional Calculations

Single crystal growth of 4-aminobenzophenone (ABP) by micro-capillary Czochralski melt technique for second harmonic generation (SHG) applications

Thermal stability and dispersion of CeO2 supported on Al2O3 is greatly improved by insertion of ZrO2 into the CeO2 lattice. It is shown that homogeneous nanosized CexZr1-xO2 solid solutions can be prepared on the Al2O3 surface by using a citrate complexation synthesis method. Investigation of effects of CexZr1-xO2 composition and loading of the Ce0.2Zr0.8O2 phase on thermal stability and nanostructure of the prepared materials revealed that strong interactions between the supported phase and Al2O3 are induced by the high-temperature treatment. High contents of ZrO2, choice of the CexZr1-xO2 precursors, and loading of the mixed oxide are critical factors leading to nanocomposite systems with high thermal and structural stability, consisting of particles of Ce0.2Zr0.8O2 as small as 9−20 nm in close contact with a θ-Al2O3 matrix even after calcination at 1373 K. The enhanced stability of the present materials was confirmed also under hydrothermal conditions.

Molecular vibrational polaritons, a hybridized quasiparticle formed by the strong coupling between molecular vibrational modes and photon cavity modes, have attracted tremendous attention in the chemical physics community due to their peculiar influence on chemical reactions. At the same time, the half-photon half-matter characteristics of polaritons make them suitable to possess properties from both sides and lead to new features that are useful for photonic and quantum technology applications. To eventually use polaritons for chemical and quantum applications, it is critical to understand their dynamics. Due to the intrinsic time scale of cavity modes and molecular vibrational modes in condensed phases, polaritons can experience dynamics on ultrafast time scales, e.g., relaxation from polaritons to dark modes. Thus, ultrafast vibrational spectroscopy becomes an ideal tool to investigate such dynamics. In this Perspective, we give an overview of recent ultrafast spectroscopic works by our group and others in the field. These recent works show that molecular vibrational polaritons can have distinct dynamics from its pure molecular counterparts, such as intermolecular vibrational energy transfer and hot vibrational dynamics. We then discuss some current challenges and future opportunities, such as the possible use of ultrafast vibrational dynamics, to understand cavity-modified reactions and routes to develop molecular vibrational polaritons as new room temperature quantum platforms.

Studies on the thermal stability and decomposition kinetics of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide via density functional theory and experimental methods

We study a hybrid system of a plasmonic cavity coupled to a pair of different molecular vibration modes with the strong optomechanical-like interactions. Here, this plasmonic cavity is considered as a quantum data bus and then assist several applications. For instance, it can first establish a bimolecular interface to ensure the reciprocal or non-reciprocal information transmission, and then engineer both molecules into the steady-state quantum entanglement of the continuous variable through the dissipative method. In contrast to the traditional optomechanical system, this hybrid system can provide the stronger optomechanical-like interactions and more convenient controls to the molecular quantum units. This investigation is believed to be able to further expand the practical application range of quantum technology.

The thermal decomposition processes for ten pyrimidine nucleoside analogs were measured with thermogravimetry and differential scanning calorimetry. The IR spectra, high-performance liquid chromatography, and liquid chromatography–mass spectrometry of pyrimidine nucleoside analogs and their residues of thermal decomposition at various temperatures were determined. The molecular bond orders of pyrimidines and pyrimidine nucleoside analogs were calculated with an ab initio method from the GAMESS program. We then discuss mechanisms of thermal decomposition in these pyrimidine nucleoside analogs. The results indicate that there are four types of mechanisms. The decomposition mechanism depends on the relative strength of the peptide bond and the amide bond within pyrimidine ring and whether or not accompanied by oxidation reaction. The substituent groups affect the thermal stability and the thermal decomposition mechanism of pyrimidine nucleoside analogs. Increasing the number of electron-donating groups on the pyrimidine ring and furan ring will enhance the peptide bond, and will elevate the temperature of thermal decomposition. There is a positive correlation between the molecular bond orders calculated by quantum chemistry and the thermal decomposition temperature of pyrimidine nucleoside analogs. The stronger the weakest bond order, the higher the decomposition temperature. The molecular bond orders thus can be used as a basis to judge molecular thermal stability for analog compounds with similar molecular structure, size, and energy.

Pharmaceutical cocrystals have attracted extensive interest to optimize the physicochemical properties of active pharmaceutical ingredients (APIs), which benefits nonsteroidal anti-inflammatory drugs (NSAIDs) by linking them with cocrystal formers (CCFs) via intermolecular interactions. The energy level matching between terahertz (THz) photons and intermolecular interactions makes THz spectroscopy sensitive to characterizing API-CCF cocrystals by spectral fingerprint. However, the limited frequency bandwidth and temperature range restrict the comprehensive understanding of spectral evolution and the molecular vibrational pattern. In this work, THz time-domain spectroscopy (THz-TDS) and synchrotron radiation-based broadband THz (SRBB-THz) are combined to extend the frequency range to 0.5-18 THz. A naproxen-proline (NAP-Pro) cocrystal is selected to conduct experiments from room temperature to 4.2 K. As the temperature decreases, the spectral evolution is characterized by peak sharpening, new peak appearance, peak shift, and peak splitting. The parameters of full width at half maximum (FWHM) and frequency shift are quantitatively fitted by a quadratic function and Bose-Einstein statistics, respectively. Quantum chemical calculations are further carried out to assign fingerprint frequencies to specific molecular vibrations, where collective vibrational modes govern low frequencies of 2-6 THz and individual modes dominate high frequencies of 6-17 THz. Based on oscillation theory, this is attributed to distinct force constants with respect to a specific vibrational mode. This study elucidates the evolutionary pattern of temperature-induced spectral features and molecular vibrational modes, which is insightful for investigating the pharmaceutical cocrystal system and systematically understanding the THz spectral characteristics.

Vibrational strong coupling and the formation of vibrational polaritons are a result of strong light-matter interaction between a cavity photon and a molecular vibrational mode. The Rabi splitting parameter, which reflects the microscopic light-matter interaction strength, reveals information about the molecular alignment and concerted vibrational motion inside the cavity. We have investigated vibrational strong coupling of 4-cyano-4'-octylbiphenyl liquid crystal molecules in isotropic and smectic A phases. We observed a ∼30% change in the Rabi splitting with the phase transition from isotropic to smectic A by controlling the temperature, together with the onset of polarization-dependent anisotropy of the Rabi splitting in the smectic A phase. Based on the estimated orientational distribution function, we show that the observed Rabi splitting difference in the isotropic and smectic A phases can only be explained by taking into account the influence of collective vibrational motion in the cavity, which affects the molecular properties under the vibrational strong coupling regime.