Non-Covalent Interaction: Revealed by Rotational Spectroscopy

The pulsed jet Fourier transform microwave spectroscopy have been applied to several molecular complexes involving H2O, freons, methane, carboxylic acids, and rare gas. The obtained results showcase the suitability of this technique for studying the intermolecular interactions. The rotational spectra of three water adducts of halogenated organic molecules, i.e. chlorotrifluoroethylene, isoflurane and alfa,alfa,alfa,-trifluoroanisole, have been investigated. It has been found that, the halogenation of the partner molecules definitely changes the way in which water will link to the partner molecule. Quadrupole hyperfine structures and/or the tunneling splittings have been observed in the rotational spectra of difluoromethane-dichloromethane, chlorotrifluorometane-fluoromethane, difluoromethane-formaldehyde and trifluoromethane-benzene. These features have been useful to describe their intermolecular interactions (weak hydrogen bonds or halogen bonds), and to size the potential energy surfaces of their internal motions. The rotational spectrum of pyridine-methane pointed out that methane prefers to locate above the ring and link to pyridine through a C-H•••π weak hydrogen bond, rather than the C-H•••n interaction. This behavior, typical of complexes of pyridine with rare gases, suggests classifying CH4, in relation to its ability to form molecular complexes with aromatic molecules, as a pseudo rare gas. The conformational equilibria of three bi-molecules of carboxylic acids, acrylic acid-trifluoroacetic acid, difluoroacetic acid-formic acid and acrylic acid-fluoroacetic acid have been studied. The increase of the hydrogen bond length upon H→D isotopic substitution (Ubbelohde effect) has been deduced from the elongation of the carboxylic carbons C•••C distance. The van der Waals complex tetrahydrofuran-krypton shows that the systematic doubling of the rotational lines has been attributed to the residual pseudo-rotation of tetrahydrofuran in the complex, based on the values of the Coriolis coupling constants, and on the type (mu_b) of the interstate transitions.

Advanced Luminescent Materials for Technological Applications

This thesis focusses on the study of several luminescent materials and investigates some related technological applications. It is made of six chapters. Chapter 1 introduces a brief history, basic principles and applications of photoluminescence. Chapter 2 presents the photophysical properties of five benzoheterodiazole dyes. These molecules were incorporated in PMMA- and PDMS-based LSC-PV devices to determine the emission quantum yields, transmission, re-absorption and IPCE properties. DFT calculations were performed to investigate the structures and energy levels of these dyes. Chapter 3 concerns the preparation of a luminescent film to calibrate an ESA satellite that will monitor the fluorescence of terrestrial vegetation. ZnPc was selected as suitable dye to make the film. Ferrocene was selected as quencher to control the emission intensity. An industrial printing technology was used to produce large-area calibration sheets coated with green pigment that simulates the NIR reflectance of green plants in which the ZnPc is embedded. Photophysical properties of a series of alkynyl gold NHC complexes containing naphthalimide chromophore were studied in Chapter 4. All the compounds were studied in solution and solid state. Further investigations were carried out by incorporating these compounds in PMMA matrix to make films. XRD and DFT calculations were made to determine the structures and energy levels of the complexes. In chapter 5 we studied the photophysical properties of star-shaped molecular systems which can operate as molecular motors when attached onto surface, along with those of their related ligands/moieties in tetrahydrofuran solution. The photophysical properties of these molecular systems can show if they are suitable to operate as light-triggered molecular machines. Finally, chapter 6 concerns the photoluminescence behavior of three NHC half-sandwich Ir/Rh metal complexes. The photophysical properties of these compounds were examined in CH2Cl2 solutions and PMMA films. These complexes may prove potential candidates for organic phosphorescent materials.