Syntheses, quantum chemical modeling, and spectroscopic properties of wirelike, luminescent mono- and bi-metallic rhenium(I) carbyne complexes

A series of conjugated luminescent polyalkynyl organometallic complexes with mono- and bi-rhenium(I) centers that contain fac-tricarbonyl ligands and 4,4'-t-butyl-2,2'-bipyridine metal chelating units have been synthesized using the Eglington coupling reaction. These molecules contain varying numbers of -(acetylene)_n- groups (n = 1-3 for mono-metallic compounds, and n = 4-6 for the bimetallic compounds) directly attached to the metal centers. The scientific motivation for this dissertation arises from a concerted and systematic effort to create photoactive molecular wires that can serve as model systems for the understanding of electron and charge transfer through pseudo-one-dimension sp carbon chains. Therefore, the energy conduction and charge transfer properties were studied as a function of repeat acetylene units.;The photophysical and spectroscopic properties of these novel molecular wires have been fully examined. Steady-state emission and luminescence lifetime measurements have revealed that all mono- and bi-Re(I) center metallic compounds display single exponential behavior except two notable cases, compounds Re(CC)₃SiMe₃ and Re(CC) ₄Re.;In the mono-metallic compounds, the absorption spectra indicated that the S₀ → T₁, charge transfer transition is the lowest energy absorption, and there are strong spin allowed ligand (carbon-carbon triple bond) ππ* transitions for these monometallic compounds, which exhibit a red-shift as the acetylene length gets longer. Steady-state emission spectra and luminescent lifetime measurements obtained at 77 K as well as the quantum chemical modeling studies revealed that an admixture of 3LLCT (π_C≡C → π*_bpy) & 3MLCT (d_Re → π*_bpy) constitutes the lowest emitting triplet manifold for all monometallic compounds after the laser excitation. Both the conjugation effect (in terms of number of acetylene units) and the σ-donating property of the terminal group play important roles in determining the lowest-emitting manifolds.;The spectroscopic properties of bi-metallic compounds are more complicated. The observations from the excitation wavelength dependence of the steady-state emission measurements at both 77 K and 298 K, but relatively invariant of the excitation wavelength in solution strongly suggested that there exist cis- and trans-conformational isomers in these molecules. Based on DFT calculations, these conformers are highly mixed. They are trapped in the solid matrices, but are averaged out in fluid solutions. The TRIR data and computation results have revealed that lowest emitting excited state for these three bi-metallic compounds is an admixture of a dominant amount of 3LLCT (π_C≡C → π*_bpy) and a tiny amount of 3MLCT (dπ_Re → π* _bpy) transitions. The quantum chemical modeling also yields the information of the symmetry properties in the excited state of these bimetallic compounds. However, this issue cannot be fully addressed directly from the spectroscopic data.