| In this thesis, a new series of thienyl carboxylate ligated quadruply bonded dimolybdenum and ditungsten compounds have been synthesized. The effect of systematically varying the ligands in terms of number of thienyl rings, rigidity of the thienyl backbone, nature of the carboxylate tethers, and changing the metal content in the dinuclear MM core (from MM = Mo 2 to MoW to W2) have been studied.;Charge delocalization in the ground state of these compounds have been examined by electrochemical methods. Cyclic voltammetry has revealed MM-delta based reversible oxidations and ligand-pi* based quasi-reversible reductions. Further, the electronic communication in the oxidized species has been examined by electron paramagnetic spectroscopy.;The UV-Vis absorption spectra and photoluminescence spectra of the compounds show remarkable influence of the overlap between MM-delta orbitals and thienyl based pi* orbitals. Intense and broad range metal-to-ligand charge transfer is observed, which is dependent on the nature of ligand as well as on the metal content in the MM dinuclear core. Room temperature dual emission, fluorescence and phosphorescence, is observed for the dimolybdenum compounds. Other photophysical studies, including, nanosecond and femtosecond transient absorption spectroscopy, fluorescence upconversion and emission decay measurements reveal the presence of two excited states, a short lived (tau ∼ several ps), and a longer lived (tau ∼ several ns to mus) one, for all the compounds in the series. The shorter lived excited state was found to be 1MLCT, which decays by fluorescence and in addition goes on to populate a longer lived triplet excited state, which was found to be 3MMdeltadelta* in the dimolybdenum compounds. In the thienyl carboxylated compounds, when the quadruply bonded dinuclear core has MM = MoW or W2, the triplet excited state was assigned to be a 3MLCT, which decays by non-radiative processes.;Electronic structure calculations were carried out, using density functional theory and time-dependent density functional theory, on model compounds representing the series of compounds discussed above, in order to correlate the observed oxidation and reduction potentials and UV-Vis electronic transitions with the calculated frontier orbital energies and transition energies. The assignment of the lowest energy excited states and the experimentally observed electronic transition energies were found to be in good agreement with the corresponding computed values.;In addition, another novel series of quadruply bonded "bis-bis" compounds, bearing IR active functional groups, such as, -CN or -NO2 group at the terminal position of the trans-substituted ligands, were synthesized. These compounds were also characterized by electrochemical methods, electronic absorption, steady state emission and transient absorption spectroscopy. In continuation of this work, these compounds will be used in time resolved infra-red and time resolved resonance Raman spectroscopic measurements, to ascertain the extent of delocalization and the nature of their photoexcited states. |
