Intramolecular Vibrations Research Articles

PH-Responsive Nanovesicles with Enhanced Emission Co-Assembled by Ag(I) Nanoclusters and Polyethyleneimine as a Superior Sensor for Al3.

Metal nanoclusters (NCs) have been engineered as a new kind of luminescent material, whereas the application of metal NCs in aqueous solution was subjected to great limitations owing to their poor solubility, stability, and strong luminescence quenching in a single-molecule state. Herein, facile supramolecular self-assembly strategy was carried out to enhance the luminescence of Ag(I) NCs (Ag6-NCs) through multiple electrostatic interactions with polyethyleneimine (PEI). Functional colloid aggregates of Ag6-NCs such as nanospheres and nanovesicles were formed along with the enhanced emission because of the formation of compact-ordered self-assemblies, which effectively restricted intramolecular vibration of the capping ligands on Ag6-NCs to diminish the nonradiative decay. All those could block energy loss and facilitated the radiative relaxation of excited states which ultimately induced an aggregation-induced emission (AIE) phenomenon. Furthermore, the luminescent Ag6-NCs/PEI nanovesicles are pH-responsive and show a superior fluorescent sensing behavior for the detection of Al3+ with a limit of detection low to 3 μM. This is the first report about AIE of silver NCs with polymers in aqueous solution. This work sheds light on the controlled NCs-based supramolecular self-assembly and the NCs-based functional materials, which will be well-established candidates in controllable drug delivery, biomarkers, and sensors in aqueous solution.

Manifestation of cluster excitations in dielectric properties of water vapor and liquid water as well as their heat capacity

The main attention in this work is focused on the physical nature of the effective polarizability of water molecules in water vapor and liquid water. We will show that the main contribution to the effective polarizability of water vapor is formed by thermal vibration excitations of water dimers. At approaching the critical point this contribution becomes considerably greater than that caused by deformations of electron shells. In parallel with this we also show that the specific increase of the heat capacity of water vapor is mainly caused by the intramolecular vibrations and vibration excitations of water dimers. We propose a new method for the determination of dimer concentration in water vapor. This approach is generalized for the description of effective polarizability for liquid water. It is assumed that water can be considered as an ensemble of tetramers and dimers in wide temperature interval of liquid states. We analyze peculiarities of their thermal excitations in dense surroundings and their contributions to the effective polarizability of molecules. There is concentration of dimers, arising because of disintegration of tetramers, calculated.

Theoretical insight into the carrier mobility anisotropy of organic-inorganic perovskite CH3NH3PbI3

High mobility, which is highly relevant to crystal structures, is one of the predominant superiorities of organic–inorganic halide perovskites. However, the anisotropy of carrier mobility for this photoelectric material on different crystal planes is still unclear. Based on Marcus theory and Density Functional Theory, we investigated the anisotropy of carrier mobility by calculating the intramolecular vibration (namely, internal recombination energy λ) and intermolecular electronic coupling integral V along a representative crystal plane. Results show that the electrons and holes exhibit consistency in the transport orientations that are parallel to the (010), (101), and (110) crystal planes. However, inconsistency was observed in those parallel to the (111) and (001) crystal planes (with an angle of approximately 60°) between the electron and hole transport directions This condition is unfavorable to the balancing of the transport and collection of photoinduced carriers. Our work reveals the theoretical significance of control-oriented growth of perovskites.

The influence of interactions between isotopoloques on coherent, ultrafast vibrational dynamics of liquid C2Cl4.

The dynamics of intramolecular and intermolecular vibrations in liquid tetrachloroethylene are studied for the first time by use of femtosecond time-resolved techniques, such as transient transmission spectroscopy and optical Kerr effect spectroscopy. Fourier transforms of time signals are compared with spontaneous Raman spectra for both isotropic and anisotropic components. The isotopic effect resulting from natural abundance of chlorine isotopes manifests itself as splitting of the isotropic spectra of intramolecular symmetric vibrations. Application of windowed Fourier transform enables us to study the dynamics of both spectral responses in real time and to analyze the role of intermolecular interactions on the coherence in the system. In order to describe the dynamics of molecules in a liquid and to explain the experimental results, we use a simple theoretical model taking into account intermolecular interactions, which allowed us to find vibrational and rotational life times.

Колебательные и тепловые свойства оксианионных кристаллов

AbstractThe vibrational and thermal properties of dolomite and alkali chlorates and perchlorates were studied in the gradient approximation of density functional theory using the method of a linear combination of atomic orbitals (LCAO). Long-wave vibration frequencies, IR and Raman spectra, and mode Gruneisen parameters were calculated. Equation-of-state parameters, thermodynamic potentials, entropy, heat capacity, and thermal expansion coefficient were also determined. The thermal expansion coefficient of dolomite was established to be much lower than for chlorates and perchlorates. The temperature dependence of the heat capacity at T > 200 K was shown to be generally governed by intramolecular vibrations.

Exploration of biocompatible AIEgens from natural resources.

Luminogens with aggregation-induced emission (AIEgens) characteristics have been well developed and applied in various areas such as bio-imaging, theranostics, organic photoelectronics and chemo/bio sensors. However, most of the reported AIEgens suffer from the disadvantages of complex organic synthesis and high cost, as well as being environmentally unfriendly and hard to degrade, which have largely limited their real applications. In this work, we discovered berberine chloride, a natural isoquinoline alkaloid isolated from Chinese herbal plants, as an unconventional rotor-free AIEgen with bright solid-state emission and water-soluble characteristics. Single crystal structure analysis and optical property, viscosity, and host-guest interaction studies suggested that intramolecular vibration and twisted intramolecular charge transfer were responsible for the AIE phenomenon of berberine chloride. Moreover, berberine chloride was biocompatible and could specifically target lipid droplets in a fluorescence turn-on and wash-free manner, demonstrating the great potential of natural products as promising AIE probes.

Q-model of electrode reactions: altering force constants of intramolecular vibrations

A theory of redox reactions involving electron transfer between a metal electrode and a molecule in solution is formulated in terms of two types of nuclear coordinates of the thermal bath: electrostatic polarization of the medium and local low-frequency vibrations. The polarization fluctuations follow Gaussian statistics. In contrast, the vibrational coordinate is allowed to change its force constant between two oxidation states of the reactant, which is projected onto non-Gaussian fluctuations of the reactant's electronic states. A closed-form analytical theory for the electrode redox reactions is formulated in terms of three reorganization energies: the reorganization energy for the electrostatic polarization of the medium and two internal (vibrational) reorganization energies for the reduced and oxidized states of the reactant. The theory predicts asymmetry between the cathodic and anodic branches of the electrode current driven by the corresponding difference in the vibrational force constants.

Структура и колебательные свойства гидратов оксианионных кристаллов из первых принципов

AbstractStructural parameters and IR spectra of hydrates of lithium and sodium perchlorates, calcium sulfate hydrate (gypsum), and lithium nitrate hydrate are calculated ab initio using the density functional theory. The bond lengths in the water molecules are established as functions of length and energy of hydrogen bonds. The relationship between lengths of intra-anionic and hydrogen bonds is considered. The splitting of intramolecular vibrations of water is highlighted. The stretching vibration frequency of water is determined as a function of length and energy of hydrogen bonds. The combined (mixed) vibrations of anions and molecules of water with frequencies below 1400 cm^–1 are feasible as well.

Realizing enhanced luminescence of silver nanocluster-peptide soft hydrogels by PEI reinforcement.

Metal nanoclusters (NCs) are a new type of fluorescent nanomaterial composed of several to several tens of metal ions or atoms with a wide range of applications in the fields of catalysis, optics, and biomedicine. However, fluorescence quenching when existing as individuals in aqueous solutions greatly limits their applications. In this study, six-core Ag(i) NCs (Ag6-NCs) were interacted with peptides (DD-5) in water to form soft hydrogels with the aggregation-induced emission (AIE) of Ag6-NCs. The introduction of polyethyleneimine (PEI) into the Ag6-NCs/DD-5 hydrogel succeeded in further enhancing the fluorescence intensity. This dual-AIE behavior of the Ag6-NCs/DD-5/PEI hydrogels is mainly ascribed to the strong hydrogen bonding among the carboxyl groups of Ag6, those of DD-5 and the amino groups of PEI, which effectively restricted intramolecular vibration of the capping ligands on the Ag6-NCs. Moreover, the addition of PEI can effectively promote the gelation speed of Ag6-NCs/DD-5 and act as a physical cross-linker, leading to an increase of the mechanical strength of the hydrogel. This work opens a new pathway for the fabrication of smart composite materials with multiple functions, which show a variety of applications such as chemical/biosensing and bioimaging.

Ultralong-lived room temperature triplet excitons: molecular persistent room temperature phosphorescence and nonlinear optical characteristics with continuous irradiation

Heavy atom-free molecular materials with ultralong-lived room-temperature triplet excitons display nonlinear absorption using ordinary light and persistent room-temperature emission characteristics.

Structural Effects on the Spin Dynamics of Potential Molecular Qubits.

Control of spin-lattice magnetic relaxation is crucial to observe long quantum coherence in spin systems at reasonable temperatures. Such a control is most often extremely difficult to achieve, because of the coexistence of several relaxation mechanisms, that is direct, Raman, and Orbach. These are not always easy to relate to the energy states of the investigated system, because of the contribution to the relaxation of additional spin-phonon coupling phenomena mediated by intramolecular vibrations. In this work, we have investigated the effect of slight changes on the molecular structure of four vanadium(IV)-based potential spin qubits on their spin dynamics, studied by alternate current (AC) susceptometry. The analysis of the magnetic field dependence of the relaxation time correlates well with the low-energy vibrational modes experimentally detected by time-domain THz spectroscopy. This confirms and extends our preliminary observations on the role played by spin-vibration coupling in determining the fine structure of the spin-lattice relaxation time as a function of the magnetic field, for S = 1/2 potential spin qubits. This study represents a step forward in the use of low-energy vibrational spectroscopy as a prediction tool for the design of molecular spin qubits with long-lived quantum coherence. Indeed, quantum coherence times of ca. 4.0-6.0 μs in the 4-100 K range are observed for the best performing vanadyl derivatives identified through this multitechnique approach.

Voltage Losses in Organic Solar Cells: Understanding the Contributions of Intramolecular Vibrations to Nonradiative Recombinations

AbstractThe large voltage losses usually encountered in organic solar cells significantly limit the power conversion efficiencies (PCEs) of these devices, with the result that the current highest PCE values in single‐junction organic photovoltaic remain smaller than for other solar cell technologies, such as crystalline silicon or perovskite solar cells. In particular, the nonradiative recombinations to the electronic ground state from the lowest‐energy charge‐transfer (CT) states at the donor–acceptor interfaces in the active layer of organic devices, are responsible for a significant part of the voltage losses. Here, to better comprehend the nonradiative voltage loss mechanisms, a fully quantum‐mechanical rate formula is employed within the framework of time‐dependent perturbation theory, combined with density functional theory. The objective is to uncover the specific contributions of intramolecular vibrations to the CT‐state nonradiative recombinations in several model systems, which include small‐molecule and polymer donors as well as fullerene and nonfullerene acceptors.

Raman Spectroscopic Studies on Microscopic Mechanism of CP - CH4 Mixture Hydrate

The formation of methane hydrates which occur in extreme thermodynamic conditions can be considerably reduced by addition of cyclopentane (CP). To elucidate the structure, composition, cage occupancy and analyze the crystal filling process of the hydrate, Raman spectroscopy of intramolecular vibration mode for each guest species in CP- CH4 mixed-gas hydrates have been measured. The Raman spectra reveal that CP molecules occupy the large cavities (51264) and CH4 molecules only occupy the small cavities (512) sII hydrates. The hydrogen-bonded water molecules arrange around CP molecules in the same way as in clathrate hydrate, which enhances the intrinsic enclathrate rate. The cavity occupancy and hydration number are calculated based on Raman bands area ratio. The cage occupancies of CP and CH4 reach 0.9976 and 0.2044 at 3.5 MPa, respectively. At 12 MPa, they are 0.9958 and 0.4098, respectively.

Theory of Nanoscale Organic Cavities: The Essential Role of Vibration-Photon Dressed States

The interaction of organic molecules and molecular aggregates with electromagnetic fields that are strongly confined inside optical cavities within nanoscale volumes, has allowed the observation of exotic quantum regimes of light-matter interaction at room temperature, for a wide variety of cavity materials and geometries. Understanding the universal features of such organic cavities represents a significant challenge for theoretical modelling, as experiments show that these systems are characterized by an intricate competition between coherent and dissipative processes involving entangled nuclear, electronic and photonic degrees of freedom. In this review, we discuss a new theoretical framework that can successfully describe organic cavities under strong light-matter coupling. The theory combines standard concepts in chemical physics and quantum optics to provide a microscopic description of vibronic organic polaritons that is fully consistent with available experiments, and yet is profoundly different from the common view of organic polaritons. We show that by introducing a new class of vibronic polariton wave functions with a photonic component that is dressed by intramolecular vibrations, the new theory can offer a consistent solution to some of the long-standing puzzles in the interpretation of organic cavity photoluminescence. Throughout this review, we confront the predictions of the model with spectroscopic observations, and describe the conditions under which the theory reduces to previous approaches. We finally discuss possible extensions of the theory to account for realistic complexities of organic cavities such spatial inhomogeneities and the multi-mode nature of confined electromagnetic fields.

A DFT study of a set of natural dyes for organic electronics.

We systematically investigate, at density functional theory level, the electronic properties of a set of ten carotenoid molecules with different conjugation length. Ground state geometries were fully optimized using both B3LYP and its long-range corrected version, i.e., the CAM-B3LYP functional. The time-dependent DFT approach (TD-DFT) was also performed for the calculation of the excited states of the optimized geometries and the results were compared to the experimental ones, when available. Our findings indicate a dependence of the transition vertical energies, oscillator strengths, and transition dipole moments on the extension of conjugation, as expected. We also investigate the impact of the intra-molecular vibrations on the absorption spectrum by means of the Franck-Condon (FC) and nuclear ensemble (NE) approach to spectra simulation. Our simulations suggest that the Franck-Condon approximation may not be suitable to appropriately characterize the vibronic progression of these molecules, whereas the NE approach provides a contribution that vary from negligible to meaningful depending on which molecule and energy region is under analysis.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer.

Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

Chromophore-Dependent Intramolecular Exciton-Vibrational Coupling in the FMO Complex: Quantification and Importance for Exciton Dynamics.

In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.

Simulated Raman spectra of four tetraphenylbutadiene polymorphs

AbstractWe report a combined experimental and theoretical investigation on the Raman spectra of the polymorphs α, β, γ, and δ of 1,1,4,4‐tetraphenyl‐1,3‐butadiene (TPB), in the region of the intramolecular modes. The interpretation of the polarized spectra is supported by ab‐initio calculations for the isolated molecules and by lattice dynamics calculations for the crystals. The calculations reproduce the peculiar, and surprisingly large, differences among the spectra of the various polymorphs. The phenyl groups of 1,1,4,4‐tetraphenyl‐1,3‐butadiene may arrange themselves around the butadiene skeleton in 2 stable conformers, which have either inversion (Ci) or 2‐fold (C2) symmetry and therefore exhibit intramolecular vibrations with quite different Raman selection rules and spectra. The compound forms 4 crystalline polymorphs (α, β, γ, and δ) with different combinations of Ci and C2 conformers, and correspondingly different intramolecular spectra. The theoretical calculations provide a quantitative analysis of the various spectra.

Discerning Inter- and Intramolecular Vibrations of Sulfur Polyaromatic Compounds.

Thiophenes are an important class of molecules in fields as diverse as petrochemistry, molecular electronics, and optoelectronics. Thiophenic submolecular motifs are thought to play a role in molecular association and nanoaggregation phenomena in both pure materials and natural and synthetic mixtures. Vibrational (infrared and Raman) spectroscopy provides the means to characterize these species. In this work far-infrared photoacoustic and low-frequency Raman spectra of a series of polycyclic aromatic hydrocarbons containing sulfur have been measured and interpreted using DFT calculations based on a perturbational-variational method coupled with potential truncation. The approach and outcomes illustrate how inter- and intramolecular vibrations for thiophenic systems in single and multicomponent mixtures can be discriminated. This work offers the perspective to search the inter- and intramolecular signatures of the main submolecular motifs and heteroelements postulated as being present in the asphaltenes.

Pressure-Induced Emission Enhancement of Carbazole: The Restriction of Intramolecular Vibration.

Pressure-induced emission enhancement (PIEE), a novel phenomenon in the enhancement of the solid-state emission efficiency of fluorophores, has been arousing wide attention in recent years. However, research on PIEE is still in the early stage. To further pursue more enhanced efficiency, discovering and designing more PIEE systems would be urgently desirable and of great importance. In this Letter, we found that carbazole presented a conspicuous emission enhancement under high pressure up to 1.0 GPa. In situ high-pressure infrared spectroscopy and angle-dispersive X-ray diffraction analysis combined with Hirshfeld surface theory calculation indicated that the PIEE of carbazole was attributed to the decrease of the nonradiation vibration process. This phenomenon mainly resulted from restriction of the N-H stretching vibration by increased N-H···π interactions under high pressure. Our study puts forward a mechanism of PIEE related to the restriction of intramolecular vibration, which provided deep insight into the essential role of intermolecular interaction in fluorescence emission properties.