Alytis Gruodis

Spectroscopy of self-trapped charge-transfer excitons in polar films and crystals of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI)

The origin of exciton states in crystals built up by dipolar N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) molecules has been investigated by means of absorption and luminescence spectroscopy. The exciton spectral and dynamical properties in the solid state are compared to those of the excitation of separated DMABI molecules embedded in a rigid polymer matrix. The luminescence excitation spectra and the luminescence decay kinetics are discussed on the basis of the specific adiabatic potential-energy scheme of the self-trapped excitons.

The conformers of chloromethylmethyldifluorosilane studied by vibrational spectroscopy and ab initio methods

Chloromethylmethyldifluorosilane (CH2ClCH3SiF2) was synthesized for the first time. Raman spectra of the liquid were recorded at various temperatures between 298 and 175 K and spectra of the amorphous and crystalline solids were obtained. Infrared spectra were recorded in the vapour, amorphous and crystalline solid phases in the MIR and FIR regions. Additional MIR spectra of the compound isolated in argon and nitrogen matrices were obtained at 10 K. The spectra of chloromethylmethyldifluorosilane showed the existence of two conformers, anti and gauche, present in the vapour and in the liquid. By careful annealing the amorphous solid formed by depositing the vapour on a cold Cu finger (Raman) or on CsI or silicon windows (infrared) at 80 K, two different crystals were formed. One of these, obtained after annealing to 125 K (crystal I), contained the anti conformer; the other, achieved after annealing to ca 170 K (crystal II), contained molecules in the gauche conformation. If the liquid was cooled, crystal II was formed, suggesting this crystal to be stable, whereas crystal I appeared to be metastable. The anti and gauche conformers had approximately the same enthalpy in the liquid, giving a negligible ΔH (gauche–anti) equal to 0.2 ± 0.4 kJ mol−1, but gauche was the conformer of the stable crystal II. Intensity variations in the matrix spectra after annealing indicated that gauche was the low-enthalpy conformer in both matrices and probably also in the vapour. These experimental data make a very reliable assignment of the conformer bands possible. Ab initio calculations were performed at the HF/6–311G* level, from which optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers were obtained. The conformational energy derived was 5.9 kJ mol−1, with gauche being the low-energy conformer. Copyright

Conformational studies of aliphatic secondary ozonides (propene, 1-butene and 1-heptene) by means of FTIR spectroscopy

Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position.

Spectroscopy of excitons in the polar molecular crystal DMABI

This paper considers the origin of the excited states and spectroscopic features of polar molecular compounds of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI). Evidence of a strong exciton-phonon interaction and its effects on the exciton absorption and luminescence spectra was discovered. The spectral features were related to the crystal structure and were ascribed to self-trapped charge transfer excitons. A weak, narrow luminescence line was also observed in resonance with the lowest absorption band and was attributed to free exciton radiative recombination.

Relaxation of self‐trapped excitons in polar molecular compounds

The origin of the excited states in polar molecular compounds of N,N‐dimethylaminebenzylidene 1,3‐indandione (DMABI) has been investigated. The spectral, kinetic and polarization properties of the of self‐trapped exciton luminescence were discussed with special glance to the crystal structure of DMABI. The build up of DMABI crystal of α‐modification predetermines increased intermolecular interaction between donor and acceptor fragments of neighboring DMABI molecules. The intermolecular charge transfer transition was found to take place simultaneously with considerable intramolecular charge redistribution because of chemically bonded donor and acceptor fragments within polar DMABI molecule. A week, narrow luminescence line was observed in resonant with the lowest absorption band and was attributed to the free exciton radiative recombination. By increasing the excitation intensity the onset of non‐linear bimolecular annihilation of excitons was observed.

On the stability of the hydrogen chloride complexes with ethylene and acetylene. A high resolution gas phase and ab initio study

The temperature dependencies of the intensities of the HCl stretching bands of the hydrogen chloride complexes with acetylene and ethylene have been used to obtain estimates of the dissociation enthalpies of the two complexes. Quantum chemical calculations on the Hartree Fock and DFT/B3LYP levels of theory have been combined with experimental data to give estimates of the intensities of the HCl stretching vibration in the two complexes.

Excitation Dynamics in Solutions, Films and Crystals of Indandione-1,3 Pyridinium Betaine

Abstract The excitation decay kinetics of polar Indandione-1,3 Pyridinium Betaine (IPB) molecules in various environments: solvents, films and crystals, were studied using time-resolved luminescence and transient absorption measurements. A red-shift, depolarization and fast decay of the luminescence intensity were observed on a femtosecond time scale in dilute solutions and explained by excitation relaxation from the initially created intramolecular charge transfer state to the lower energy excited state of the indandione moiety. The first fast relaxation stage is followed by a slower one responsible for the relaxation to the ground state stage with the rate depending on the viscosity of the surrounding. By comparing the excitation properties of IPB in solution and those in the crystal form, the influence of the intermolecular interactions on the excited state dynamics is revealed. Excitation relaxation in the IPB deposited films of different thickness and in a single crystal is described as a competition between different relaxation paths of nonradiative recombination, these paths being the high lying Frenkel exciton states and the low lying intermolecular charge transfer states.

Optical properties of films built up by polar molecules

The origin of the excited states and the spectroscopic features of polar molecular films and crystals of N,N- dimethylaminobenzylidene 1,3-indandione (DMABI) was considered. The formation of charge transfer exciton states in the absorption and luminescence spectra by increase of the thicknesses of DMABI films was observed. The evidence of a strong exciton-phonon interaction and its effects on the exciton absorption and luminescence spectra was discovered. The coexistence of free and self-trapped excitons at elevated temperatures was found in DMABI films. The dynamics of both shallow short-lived and deeply trapped long-lived self-trapped exciton states in various films and crystal of DMABI was discussed.

Graphene, Fullerenes, Carbon Nanotubes: Electronic Subsystem

This chapter introduces the reader to the analysis of the structural and electronic system properties of various carbon allotropes (CNT, graphene) and several molecular derivatives. The genesis of the electronic system formation is investigated in detail. Non-regular defected nanocarbon systems are considered for possible applications in different fields, including energy storage; chemical, biochemical and electrochemical sensing; water purification; and catalysis.

Surface Nanophysics: Macro-, Meso-, Micro- and Nano-approaches

The surface factor is very important for manipulating objects at a nanoscale. Thermodynamic behaviour is observed from the classical point of view, and conditional division into macro-, meso-, micro- and nano-approaches is presented. Processes of physical and chemical adsorption on the surface are presented from the energy and structure aspects. The occurrence of electronic states of the surface is presented from the classical point of view in comparison with molecular electronic states. One of the most important non-invasive optical methods to investigate nanoparticles is the surface plasmon resonance (SPR), which is quite useful for practical detection of nanoparticles in the surrounding environment. The interaction of light with nanoparticles is discussed within the framework of a nanoscale process. Nanoshells as practical implementation of nanosurface phenomena are discussed.