Rational design, synthesis, and characterization of functional chelating cages and linear polymers

The research in this thesis was focused on designing purely organic, as well as transition metal-complex based materials at the molecular level, with controlled topology (hemicages and rigid rods) and specific photophysical, photochemical and/or electrochemical characteristics. The immediate objective was to obtain a systematic understanding and rational design of these materials. The long term goal was to apply these materials to various functional devices (light emitting, electrochromic, photovoltaic devices, sensors, electrocatalysts, etc.) The first half of the thesis describes the syntheses and characterization of a new hemicage 8-hydroxyquinoline ligand and its Al3+, Ga 3+, and In3+ complexes. This ligand's tripodyl structure enabled the synthesis and characterization of purely facial isomers of these complexes. These isomers exhibited enhanced electrochemical stability and a 26-79% increase in the photoluminescence quantum efficiency. Consequently, the caged metal complexes, especially with Al3+, can potentially replace Alq3 in OLEDs, due to decreased thermal hydrolysis and electrochemical degradation when compared to the uncaged Alq3. In order to better understand the structure property relationships of these 8-hydroxyquinoline-based complexes and to further conduct judicious ligand engineering for device performance optimization, a series of ligand modifications were conducted. The modifications included: (1) attaching side chains to the quinoline ring to adjust the solubility and even to tune the emission color (2) changing the connecting cap from benzene to a single carbon atom to form more rigid structures and (3) fusing pinene moieties to the quinoline to produce chiral cages.The second half of the thesis addresses a combined experimental-computational study of polynuclear [Run(TPPZ)n +1]2n + complexes with n = 1, 2, 3 and n > 5, which are of interest to the field of photoactive polymers. In the UV-Vis spectrum, a red-shift of the visible band maximum from 2.59 to 2.03 eV was observed, going from the monomer to the longer oligomeric species ( n > 5). To characterize the geometries, electronic structure, and excited states of these complexes, density functional theory (DFT) and time-dependent DFT calculations were performed. The main band in the visible region is assigned as a metal-to-metal plus ligand charge transfer (MMLCT) transition. The resulting excited states are delocalized throughout the entire complex, as they originate from a superposition of pi*(TPPZ)-t2g(Ru) states. The [Osn(TPPZ) n+1]2n + complexes showed a similar spectroscopical behavior to their Ru counterparts, with differences at longer wavelength due to their relaxed singlet-triplet transitions.In order to enhance the intermetallic interaction throughout the polymer, three new TPPZ derivatives with expanded pi-conjugation were also synthesized. This was followed by the formation of their Ru(II) and Os(II) complexes, including monomers, dimers, trimers, and polymers. Their electronic absorption properties were measured by UV-vis and compared with corresponding TPPZ complexes. One remarkable finding is that, for [Osn(4,5-BenzoTPPZ) n+1]2n + complexes, certain formally forbidden transitions (assigned as 3MMLCT) are extensively red-shifted and progressively intensified with the increase in the number of n. These transitions eventually become the predominant absorption band in the visible/near-infrared region of the spectrum. This observation makes the Os-4,5-BenzoTPPZ polymer a good candidate for application as molecular wires.