A series mixed metal supramolecular complexes were synthesized and studied by electrochemistry, photophysics and photochemistry. The complexes consisted of a single RuII or OsII polyazine light absorber bound to a cis-RhIIICl2 moiety through a polyazine bridging ligand. A related class of supramolecule is known to perform photoinitiated electron collection, photocatalysis of hydrogen from water, DNA photomodification and is known to kill mammalian cells; all with visible light irradiation. The complexes studied herein, [(bpy)2Ru(bpm)RhCl2(phen)](PF6)3, [(bpy)2Ru(dpp)RhCl2(phen)](PF6)3, [(bpy)2Os(dpp)RhCl2(phen)](PF6)3, and [(tpy)OsCl(dpp)RhCl2(phen)](PF6)2 were synthesized in moderate yields (54-84%) by reaction of the appropriate monometallic visible light absorbing subunit with a slight excess of K[(phen)RhCl4]·3H2O (bpy = 2,2'-bipyridine, bpm = 2,2'-bipyrimidine, 1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine, and tpy = 2,2':6',2"-terpyridine). Voltammetric analysis of [(bpy)2Ru(bpm)RhCl2(phen)](PF6)3 revealed a reversible oxidation at 1.76 V (vs. Ag/AgCl) (RuIII/II). A reversible reduction at â 0.14 V (bpm0/-), and quasi-reversible reductions at â 0.77 V and â 0.91 V each corresponded to a one electron process, bpm0/â , RhIII/II and RhII/I. The electrochemistry of [(bpy)2Ru(dpp)RhCl2(phen)](PF6)3 showed a reversible oxidation at 1.61 V (RuIII/II), and quasi-reversible reductions at â 0.39 V, â 0.74 V and â 0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. [(bpy)2Os(dpp)RhCl2(phen)](PF6)3, and [(tpy)OsCl(dpp)RhCl2(phen)](PF6)2 each exhibited reductions similar to the dpp bridged Ru,Rh dyad, but with OsIII/II based oxidations at 1.24 V and 0.83 V, respectively. The complexes [(bpy)2Ru(bpm)RhCl2(phen)](PF6)3 and [{(bpy)2Ru(bpm)}2RhCl2](PF6)5 display Ru(dπ)â bpm(π*) CT (MLCT) transitions at 581 nm and at 594 nm, respectively. The dpp bridged Ru,Rh bimetallic and Ru,Rh,Ru trimetallic display Ru(dπ)â dpp(π*) CT transitions at 509 nm and 518 nm, respectively. Similarly, [(bpy)2Os(dpp)RhCl2(phen)](PF6)3 absorbs strongly at 520 nm versus 534 nm for [{(bpy)2Os(dpp)}2RhCl2](PF6)5, both with low energy tails at 800 nm indicative of Os centered MLCT transitions. Overlapping Os(dπ)â dpp(π*) and Os(dπ)â tpy(π*) transitions occur at 536 nm with low energy tails at 856 nm for both [(tpy)OsCl(dpp)RhCl2(phen)](PF6)2 and [{(tpy)OsCl(dpp)}2RhCl2](PF6)3. Emission from [{(bpy)2Ru(dpp)}RhCl2](PF6)5 and [(bpy)2Ru(dpp)RhCl2(phen)](PF6)3 at room temperature and 77 K was red shifted and less intense than emission from [(bpy)2Ru(dpp)Ru(bpy)2](PF6)4, consistent with quenched emission from a Ru(dπ)â dpp(π*) 3MLCT state. Transient absorption spectroscopy supported assignment of the emissive state as Ru(dπ)â dpp(π*) CT in nature. The complexes [(bpy)Ru(dpp)RhCl2(phen)](PF6)3 (τ =18 ns) and [{(bpy)2Ru(dpp)}2RhCl2](PF6)5 (τ = 16 ns) each exhibit shorter lived 3MLCT states than the Ru,Ru dyad (τ = 125 ns) in acetonitrile consistent with favorable electron transfer to Rh(III) to generate a metal to metal charge transfer (3MMCT) state. The photochemistry of [{(bpy)2Ru(dpp)}2RhCl2]Cl5, [{(tpy)OsCl(dpp)}2RhCl2]Cl3, [(bpy)2Ru(dpp)RhCl2(phen)]Cl3, and [(tpy)OsCl(dpp)RhCl2(phen)]Cl2 with DNA was investigated using gel electrophoresis and selective precipitation of a DNA/metal complex adduct. An array of high intensity LEDs was designed, constructed and validated to accommodate these high throughput photochemical experiments with DNA. Each of the metal complexes is suggested to undergo photobinding with DNA as well as to photocleave DNA. A 3MMCT state or a thermally accessible Rh centered 3LF state each are proposed as leading to photobinding, while a 3MMCT state is thought to be involved in DNA photocleavage. / Ph. D.

A series of mixed-metal bimetallic complexes [(TL)2M(dpp)RhCl2(TL)]3 (M = Ru and Os, terminal ligands (TL) = phen, Ph2phen, Me2phen and bpy, terminal ligands (TL) = phen, bpy and Me2bpy ), which couple one Ru or Os polyazine light absorber (LA) to a cis-RhIIICl2 center through a dpp bridging ligand (BL), were synthesized using a building block method. These are related to previously studied trimetallic systems [{(TL)2M(dpp)2RhCl2]5+, but the bimetallics are synthetically more complex to prepare due to the tendency of RhIII halide starting materials to react with diimine ligands to form cis-[Rh(NN)2Cl2]+ motifs. The bimetallic complexes, [(phen)2Ru(dpp)RhCl2(bpy)]3+, [(phen)2Ru(dpp)RhCl2(phen)]3+, [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+, [(Me2phen)2Ru(dpp)RhCl2(phen)]3+, [(bpy)2Ru(dpp)RhCl2(bpy)]3+, [(bpy)2Ru(dpp)RhCl2(Me2bpy)]3+ and [(bpy)2Os(dpp)RhCl2(phen)]3+, were characterized and studied by electrochemistry, electronic absorption spectroscopy, ESI-mass spectrometry, steady-state and time-resolved emission spectroscopy. Ï¿" ï¿" The electrochemical properties of bimetallic complexes with polyazine ligands exhibit a reversible one-electron metal-based oxidation, a quasi-reversible RhIII/IICl2 overlapped with a small amount of RhII/ICl and an irreversible RhII/ICl2 �reductions prior to the reversible bridging ligand dpp0/- �reduction. ï¿" ï¿" The title bimetallic complexes are efficient light absorbers due to the [(TL)2MII(dpp)] light absorber subunit. The bimetallics display ligand-based ï¿"'ï¿"* transitions in the UV region and metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum with approximately half the absorption extinction coefficient values relative to the trimetallics in the spectrum. The Os,Rh bimetallic complex, [(bpy)2Os(dpp)RhCl2(phen)]3+, displays Os(dï¿")'dpp(ï¿"*) CT transition at 521 nm and a low energy absorption band at 750 nm in the near-infrared region representing direct 1GS'3MLCT excitation due to the high degree of spin orbital coupling in Os complexes. The bimetallic complexes [(phen)2Ru(dpp)RhCl2(bpy)]3+, [(phen)2Ru(dpp)RhCl2(phen)]3+, [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+, [(Me2phen)2Ru(dpp)RhCl2(phen)]3+, [(bpy)2Ru(dpp)RhCl2(bpy)]3+ and [(bpy)2Ru(dpp)RhCl2(Me2bpy)]3+ display Ru(dï¿")'dpp(ï¿"*) MLCT transitions centered at 505, 508, 515, 516, 510 and 506 nm, respectively. The bimetallic complex [(Ph2phen)2Ru(dpp)RhCl2(phen)]3+ displays enhanced absorption. Ï¿" ï¿" The photophysical properties of Ru,Rh bimetallic complexes are close to those of trimetallic analogues. In room temperature acetonitrile, both bimetallic and trimetallic complexes display a weak and short-lived emission from the Ru(dï¿")'dpp(ï¿"*) 3MLCT excited state. For example, the bimetallic complex [(phen)2Ru(dpp)RhCl2(bpy)]3+ emits at 766 nm and the trimetallic complex [{(phen)2Ru(dpp)}2RhCl2]5+ emits at 760 nm. At 77 K in 4:1 ethanol/methanol glass, the bimetallics, as well as trimetallics, exhibit a more intense blue-shifted emission with a longer lifetime, which is from the same 3MLCT excited state. At 77 K, the low temperature emission from the same 3MLCT state of [{(phen)2Ru(dpp)}2RhCl2]5+ blue-shifts to 706 nm with the emission lifetime of 1.8 ms and the bimetallic [(phen)2Ru(dpp)RhCl2(bpy)]3+ emits at 706 nm (t = 1.8 ms). The Ru,Rh complexes 3MLCT excited states can populate Ru(dï¿")'Rh(ds*) triplet metal-to-metal charge transfer (3MMCT) excited states through intramolecular electron transfer at room temperature, which is impeded in the rigid matrice at 77 K due to the large reorganizational energy and restricted molecular motion. The emission of Os,Rh bimetallic complex [(bpy)2Os(dpp)RhCl2(phen)]3+ could not be detected by our instruments likely due to its expected red-shifted emission which lies outside our detector window. ï¿" ï¿" �The Ru,Rh bimetallics display interesting and efficient photo-reactivity with DNA activated by visible light. The DNA gel shift assay, selective precipitation, ESI-mass spectrometry and polymerase chain reaction (PCR) studies suggest that Ru,Rh bimetallic complexes photobind to DNA following visible light excitation. This reactivity is not observed for analogous Ru,Rh,Ru trimetallics due to the steric protection of the Rh site in that motif. The bimetallic [(TL)2Ru(dpp)RhCl2(TL)]3+ systems can photobind and photocleave DNA through low-lying 3MMCT excited states when excited by the low energy visible light, with or without molecular oxygen. This is unusual but desirable reactivity for photodynamic therapy (PDT) drug development. The Os,Rh bimetallic complex [(bpy)2Os(dpp)RhCl2(phen)]3+ photobinds and photocleaves DNA under red therapeutic light excitation without molecular oxygen, an unprecedented result. Polymerase chain reaction experiments were used to evaluate the impact on DNA amplification of the DNA photo-modification and photo-damage induced by [(bpy)2Os(dpp)RhCl2(phen)]3+ under red light irradiation. Either photobinding or photocleavage induced by red light excitation of [(bpy)2Os(dpp)RhCl2(phen)]3+ on DNA inhibits amplification via PCR methods, a model for in vivo replication. Moreover, significant thermal stability of DNA photo-modification over 90 "C is required for PCR. A red light-activated drug that acts in an oxygen-independent mechanism to impede DNA amplification is unique in this field and desirable for study as a new class of PDT drugs. / Ph. D.

A series of bimetallic (Ru^II, Pt<sup>II</sup) complexes were synthesized with the general formula [(tpy)RuCl(BL)PtCl₂](PF₆) (tpy = 2,2':6',2"-terpyridine and BL = bridging ligand) and their spectroscopic, electrochemical, and DNA binding properties studied. The bridging ligands used in these complexes were 2,3-bis(2'-pyridyl)pyrazine (dpp), 2,3-bis(2'-pyridyl)quinoxaline (dpq) and 2,3-bis(2'-pyridyl)benzoquinoxaline (dpb). These complexes combine light-absorbing Ru^II-polypyridyl chromophores and a cis-PtCl₂ structural motif known to bind DNA. The Ru-bound chloride may be substituted, enabling further modification of the spectroscopic properties. The synthesis of [(tpy)RuCl(BL)PtCl₂](PF₆) utilizes a building block approach that allows modifications to the series of complexes within the general synthetic scheme. This illustrates the applicability of this scheme to the development of new series of complexes. The lowest-energy absorption for the three complexes is assigned to a Ru(dπ) → BL(π*) charge transfer transition. This transition shifts to lower energy as the ligand is varied from dpp to dpq to dpb. The first and second reductions are BL^0/- and BL^-/2- based and shift to more positive potentials from dpp to dpq to dpb. The Ru^II/III redox couple remains at a nearly constant potential for the series. All three compounds show DNA binding when incubated with linearized plasmid DNA. Adduct formation was assessed by agarose gel electrophoresis as a retardation of band migration. / Master of Science

The goal of this research was to develop structurally diverse polyazine-bridged Ru(II),Pt(II) trimetallic and tetrametallic supramolecular complexes and study the impact of component variation on the redox, spectroscopic, and excited state properties that influence photoinduced charged separation and multielectron reduction.  These complexes are active photocatalysts for H2O reduction to H2.  Tetrametallic complexes with the supramolecular architecture [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ (Ru3Pt; TL = phen = 1,10-phenanthroline or Ph2phen = 4,7-diphenyl-1,10-phenanthroline; BL" = dpp = 2,3-bis(2-pyridyl)pyrazine or dpq = 2,3-bis(2-pyridyl)quinoxaline) feature a trimetallic dpp-bridged Ru(II) light absorber coupled to a cis-PtCl2 reactive metal center.  Trimetallic complexes with one less Ru-based light absorbing unit, [{(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ (Ru2Pt; BL" = dpp or dpq), represent  a new supramolecular architecture that was designed and synthesized to provide less complex systems for excited state analysis.  Both the Ru3Pt and Ru2Pt systems have a remote Ru center separated from the reactive Pt site designed to provide extended 3MLCT lifetimes relative to directly coupled [(TL)2Ru(BL)PtCl2]2+ systems. The building block synthetic method used in constructing supramolecules provides the ability to purify and analyze the properties following each synthetic step, allowing sub-unit variation and structural diversity.  Building a knowledge base about the properties of smaller, less complicated structures is critical in understanding the electrochemistry, spectroscopy, and excited state dynamics of multi-metallic, multi-ligand complexes.  Electrochemical analysis of the [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes suggests a HOMO localized on the terminal Ru centers (E1/2 (RuII/III) = 1.56-1.63 V vs. Ag/AgCl) and a LUMO localized on the remote BL" coordinated to the reactive Pt site, with the energy dictated by the BL" identity (E1/2 = "0.32 or "0.33 V for BL" = dpp or E1/2 = "0.02 or "0.05 V for BL" = dpq).  This provides spatially separated HOMOs and LUMOs which predict lowest-lying charge separated states.  The complexes are robust UV and visible light absorbers due to multiple broad, overlapping ligand centered and metal-to-ligand charge transfer (MLCT) transitions.  The lowest energy 1MLCT absorption is centered around 540-550 nm for the four tetrametallic complexes with high molar absorptivity (31,000-42,000 M"1cm"1).  BL" variation has only a small impact on the electronic absorption spectroscopy, while the TL variation greatly enhances the absorptivity between 350 nm and 500 nm from 29,000 to 42,000 M"1cm"1 for complexes with TL = phen and Ph2phen, respectively.   The tetrametallic [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes exhibit unusual excited state dynamics as well as spatially separated HOMOs and LUMOs. The lowest lying optically populated state is a terminal Ru\'¼-dpp MLCT in all the Ru3Pt and Ru2Pt systems reported herein.  The terminal Ru(dÀ) based HOMO and BL"(À*) based LUMO suggests a lower lying terminal Ru\'BL" CS state in all systems.  Because the lowest lying terminal Ru(dÀ)\'BL"(À*) 3CS (charge separated) state is optically inaccessible, indirect population occurs.  The tetrametallic [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes have similar excited state lifetimes (Ä) of 75-83 ns, and they exhibit quantum yields of emission  ("em) of 7.1 x 10"4 (when BL" = dpp) and 3.2-3.7 x 10"4 (when BL" = dpq).  The lifetimes are shortened and the emission quantum yields are quenched in comparison to the [{(TL)2Ru(dpp)}2Ru(BL")]6+ models which possess the same emissive terminal Ru\'¼-dpp 3MLCT state with Ä = 110 ns and "em = 1.0-1.1 x 10"3.   In marked contrast to the large number of Ru polyazine systems studied, both monometallic and supramolecular complexes, the lowest lying 3MLCT state of the Ru3Pt complexes is not populated with unit efficiency due to 3CS state population from the emissive terminal Ru(dÀ)\'dpp(À*) 3CT state and a higher energy 3MLCT state, likely the central Ru(dÀ)\'BL"(À*) 3CT state.  The degree of population of this state is strongly dependent on the LUMO energy or driving force for population.  Stabilization of the BL" = dpq(À*) compared to higher energy dpp(À*) provides a larger driving force for intramolecular electron transfer to populate the 3CS state, resulting in ca. 40 % and 95 % population of the emissive state when BL" = dpq and dpp, respectively.  This suggests ca. 60 % and 5 % indirect population of the non-emissive 3CS state via a higher-lying 3MLCT state and the terminal Ru\'dpp 3MLCT emissive state when BL" = dpq and dpp, respectively.  These complexes violate Kasha\'s rule, an unusual occurrence for Ru(II) polyazine complexes, as the emissive state is not populated with unit efficiency.  Instead, the degree of population of the emissive state is dependent on the excitation wavelength. The Ru3Pt complexes are active photocatalysts for H2O reduction to H2.  In the presence of light and the sacrificial electron donor, DMA (N,N-dimethylaniline), the tetrametallic complexes collect electrons on the ligand À* orbitals of the central Ru to serve as photoinitiated electron collectors.  The photocatalytic activity in H2 production is drastically impacted by BL" identity, consistent with the enhanced driving force for charge separation to move electrons toward the cis-PtCl2 moiety.  After photolysis for 10 h, 15 ± 1 ¼mol (66 ± 4 TON) and 4 ± 1 ¼mol (18 ± 1 TON) of H2 were produced using [{(phen)2Ru(dpp)}2Ru(dpq)PtCl2]6+ and [{(phen)2Ru(dpp)}2Ru(dpp)PtCl2]6+, respectively.  Varying TL to Ph2phen serves to enhance light absorptivity and subsequently increase H2 production to 21 ± 1 ¼mol (94 ± 6 TON) and 5 ± 1 ¼mol (23 ± 2 TON) using [{(Ph2phen)2Ru(dpp)}2Ru(dpq)PtCl2]6+ and [{(Ph2phen)2Ru(dpp)}2Ru(dpp)PtCl2]6+, respectively.  The identity of BL" greatly influences the ability to direct the flow of charge through the supramolecular architecture impacting photocatalysis, while the identity of TL serves to fine tune the light absorbing and excited state properties. Due to the complicated excited state properties imparted by the large number of MLCT transitions in the [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes, the analogous [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ complexes were designed and a synthetic scheme developed.  The trimetallics possess similar electronic absorption spectroscopy with fewer terminal metal-based transitions due to removal of one (TL)2RuII(dpp) sub-unit and allow for distinguishable spectroscopic shifts resulting from perturbation of specific sub-units and the related molecular orbitals.  The trimetallic complexes exhibit similar redox properties with the HOMO localized on the terminal Ru and the LUMO localized on the remote BL", providing a low lying 3CS state.  Similar degrees of emission quenching are observed with the trimetallic complexes and their [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")]4+ models as was observed in the tetrametallic complexes.  The values of Ä and "em measured for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpp)PtCl2]4+ were 90 ns and 1.1 x 10"3, respectively, and these values were 100 ns and 5.2 x 10"4 for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpq)PtCl2]4+.  Similar to the Ru3Pt systems, the lifetimes are shortened and the emission is quenched compared to the [(Ph2phen)2"Ru(dpp)Ru(bpy)(BL")]4+ models (Ä = 120 ns and "em = 1.50 x 10"3, regardless of BL" identity).  These values provide ca. 98 % and 45 % population of the emissive state in the Ru2Pt systems for BL" = dpp and dpq, respectively, suggesting ca. 2 % and 55 % population of the non-emissive 3CS state for BL" = dpp and dpq, respectively.  This supports the use of this new Ru2Pt motif as models to study the excited state dynamics.  A substantial difference was observed between the excitation and absorption spectra for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpq)PtCl2]4+, consistent with non-unity population of the emissive 3MLCT excited state. The simplified electronic absorption spectroscopy allowed the use of nanosecond transient absorption (TA) spectroscopy to analyze the excited state, and strong evidence of violation of Kasha\'s rule through partial population of the terminal Ru(À)\'BL"(À*) 3CS state (Ä = 25 ns)  in addition to the emissive terminal Ru(dÀ)\'dpp(À*) 3MLCT state (Ä = 120 ns) was observed through excitation-based emission spectroscopy and time-resolved TA spectroscopy. The synthesis, electrochemistry, electronic absorption spectroscopy, and steady-state and time-resolved emission spectroscopy for the [2Ru(BL")PtCl2]6+ and [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ complexes as well as photocatalytic H2 production with [2Ru(BL")PtCl2]6+ and transient absorption spectroscopy of [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+, are reported herein.  The work discussed within this dissertation provides in depth knowledge about the effects of component modification on the excited state dynamics and photocatalytic activity of structurally diverse Ru3Pt and Ru2Pt supramolecular complexes that is important in developing photochemical molecular devices.  Unusual excited state dynamics make it clear that much remains to be uncovered about structure-property relationship in these complex mixed-metal, mixed-ligand supramolecular motifs.  These supramolecular motifs also have applications in photodynamic therapy drug development and are currently under investigation by members of the Brewer research group. / Ph. D.

The production of hydrogen fuel via solar water splitting is an important carbon-neutral strategy for the development of renewable resources and has sparked great interest in the scientific community. Hydrogen production efficiencies for supramolecular photocatalysts of the architecture [{(TL)2Ru(BL)}2RhX2]5+ (BL=bridging ligand, TL=terminal ligand, X=halide) are among the highest reported in deoxygenated organic solvents, but do not function in air-saturated aqueous solution due to quenching of the metal-to-ligand charge transfer (MLCT) excited-state under these conditions. Herein, we report the groundbreaking use of polyelectrolytes to increase efficiency of supramolecular photocatalysts in solar hydrogen production schemes under aqueous aerobic conditions. The new photocatalytic system incorporates poly(4-styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)2Ru(dpp)}2RhCl2]5+ (bpy = 2,2'-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine). PSS has a profound impact on photocatalyst efficiency, increasing hydrogen production over three times that of deoxygenated aqueous solutions alone. Hydrogen photocatalysis proceeds even under aerobic conditions for PSS containing solutions, an exciting consequence for solar hydrogen production research. Thermodynamics of binding due to intermolecular interactions between Ru,Rh,Ru photocatalysts and polyelectrolytes was probed using isothermal titration calorimetry (ITC). ITC studies reveal the driving forces of aggregate formation, providing new insight into the intermolecular forces that lead to increased photocatalytic efficiency and stability in the presence of water soluble polymers. Synthesis and characterization of a novel supramolecular photocatalyst having hydrophilic terminal ligands are reported. Addition of sulfonated terminal ligands into a Ru,Rh,Ru photocatalyst has a significant impact on the excited-state properties of the complex. The new complex demonstrates increased solubility and hydrogen production efficiency in aqueous solutions. Hydrogen production is observed even under aerobic conditions for the new complex, a stark contrast to the hydrophobic analog in organic solvents. The synthesis, characterization, and electropolymerization of a chromophore-catalyst assembly having vinyl-substituted terminal ligands to create robust water reduction photocatalysts on wide-bandgap semiconductors is reported. The polymeric photocatalysts are expected to show increased stability over a wide pH range and increased photostability compared to chromophore-catalyst assemblies that employ carboxylic or phosphonic acid groups to adsorb the photoreactive catalyst to the metal oxide surface. / Ph. D.

The goal of this research was to develop a series of mixed-metal supramolecular complexes with specialized light absorbing units to probe perturbation of excited-state properties by ligand deuteration and long-term complex stability via racemization of initially enantiopure light absorbing subunits. Varying bidentate polypyridyl terminal ligands (TL), bridging ligands (BL), reactive metal center (RM), or number of Ru(II) light absorbers (LA) tunes the electrochemical, spectroscopic, photophysical, and photochemical properties within the supramolecular architecture. Ru(II) monometallics of the design [(bpy)2Ru(prolinate)](PF6) utilize prolinate as a chiral directing ligand to impart chirality to the Ru(II) LAs in the synthesis of more sophisticated supramolecular complexes. Ru(II) monometallics of the design [(TL)2Ru(BL)](PF6)2 (TL = bpy or d8-bpy; BL = dpp or d10-dpp; bpy = 2,2′-bipyridine; dpp = 2,3-bis(2-pyridyl)pyrazine) covalently couple two TLs and one BL to a central Ru(II) metal center forming a LA subunit. Larger bi- and trimetallic complexes are formed by coupling an additional Ru(II), Rh(III), or Pt(II) metal center to an existing Ru(II) LA through a BL. Ru(II),Ru(II), Ru(II),Rh(III), and Ru(II),Pt(II) bimetallics of the design [(TL)2Ru(BL)Ru(TL)2](PF6)4, [(TL)2Ru(BL)RhCl2(TL′)](PF6)3, and [(TL)2Ru(BL)PtCl2](PF6)2 (TL/TL′ = bpy or d8-bpy; BL = dpp or d10-dpp) couple only one Ru(II) LA to a Ru(II), Rh(III), or Pt(II) metal center through the BL. Ru(II),Rh(III),Ru(II) trimetallics of the design [{(TL)2Ru(BL)}2RhCl2](PF6)5 (TL = bpy or d8-bpy; BL = dpp or d10-dpp) covalently couple two Ru(II) LAs to a central Rh(III) RM through polyazine BLs. The complexes discussed herein are synthesized using a building block approach, permitting modification of the supramolecular architecture through multiple synthetic steps. Electrochemical analysis of the mono-, bi-, and trimetallic complexes displays several common features: a Ru-based HOMO and either a bridging ligand or Rh-based LUMO. TL and BL modification by ligand deuteration does not affect the electrochemistry of the Ru(II), Ru(II),Ru(II), Ru(II),Rh(III), or Ru(II),Rh(III),Ru(II) complexes. Likewise, utilizing a single enantiomer of the LA subunit does not modify the redox behavior of Ru(II), Ru(II),Pt(II), or Ru(II),Rh(III),Ru(II) complexes. All of the mono-, bi-, and trimetallic complexes are efficient light absorbers throughout the UV and visible with π→π* intraligand (IL) transitions in the UV and Ru(dπ)→ligand(π*) metal-to-ligand charge transfer (MLCT) transitions in the visible. Ligand deuteration does not affect the light absorbing properties of the complexes, while incorporation of chiral LA subunits imparts a preference for circularly polarized light (CPL) absorbance into supramolecular complexes. Photoexcitation of the Ru(dπ)→dpp(π*) 1MLCT results in near unity population of short-lived, weakly emissive Ru(dπ)→dpp(π*) ³MLCT excited state. In the Ru(II), Ru(II),Ru(II), and Ru(II),Pt(II) complexes, the 3MLCT excited state relaxes to the ground state by emission of a photon or vibrational relaxation processes. In the Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) complexes, the 3MLCT excited state is efficiently quenched by intramolecular electron transfer to populate a non-emissive Ru(dπ)→'Rh(dσ*) metal-to-metal charge transfer (3MMCT) excited state. Utilizing a deuterated BL, the excited-state lifetimes and quantum yield of emission (Φem) are increased for Ru(II), Ru(II),Ru(II), Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) complexes. The Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) complexes have previously been shown to be exceptional photochemical molecular devices (PMD) for photoinitiated electron collection (PEC). The ability of these complexes to undergo multiple redox cycles, efficiently absorb light, populate reactive excited states, and collect electrons at a reactive Rh metal center fulfills the requirements for H2O reduction photocatalysts. Photolysis of the Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) complexes with 470 nm light in the presence of a sacrificial electron donor and H2O substrate yields photocatalytic H2 production. Varying the BL from dpp to d10-dpp in the bimetallic architecture results in enhanced, although relatively low, catalyst efficiency producing 40 ± 10 μL H2 with dpp and 80 ± 10 μL H2 with d10-dpp in a CH3CN solvent system after 48 h photolysis. The trimetallic architecture showed no enhancement in photocatalytic efficiency and produced 210 ± 20 μL H2 with dpp and 180 ± 20 μL H2 with d10-dpp in a DMF solvent system after 20 h photolysis. The Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) complexes' behavior differs in that the excited state lifetime is the most important factor for bimetallic catalyst functioning, but intramolecular electron transfer is the most important factor for the trimetallic photocatalysts. Another important property to understand with these catalysts is their long-term stability in solution. In order for these mixed-metal complexes to be industrially useful, they must perform for long periods of time without degradation in the presence of H2O substrate and electron donors in solution. Previous examinations of Ru(II),Rh(III),Ru(II) photocatalysts have found that they can perform for ca. 50 h of photolysis, but are not as effective as the initial few hours. Special care was taken to synthesize enantiopure LA subunits and incorporate them into Ru(II),Pt(II) and Ru(II),Rh(III),Ru(II) architectures to study their photolytic stability by monitoring how long the complexes retained their chirality using electronic circular dichroism (ECD) spectroscopy. After photolyzing for longer than 200 hours with an LED light source, the quantum yield for racemization (Φrac) for the Ru(II),Pt(II) and Ru(II),Rh(III),Ru(II) architectures is 2.6 ⨉ 10⁻⁸ and 0.72 ⨉ 10⁻⁸ respectively. Also, by photolyzing in the presence of free bpy, the bi- and trimetallic complexes racemize via a non-dissociative trigonal twist mechanism. This dissertation reports the detailed analysis of the electrochemical, spectroscopic, photophysical, and photochemical properties of a series of selectively deuterated [(TL)2Ru(BL)](PF6)2, [(TL)2Ru(BL)Ru(TL)2](PF6)4, [(TL)2Ru(BL)RhCl2(TL′)](PF6)3, and [{(TL)2Ru(BL)}2RhCl2](PF6)5 (TL = bpy or d8-bpy; BL = dpp or d10-dpp; bpy = 2,2′-bipyridine; dpp = 2,3-bis(2-pyridyl)pyrazine) supramolecular complexes and a series of [(bpy)2Ru(prolinate)](PF6), [(bpy)2Ru(dpp)](PF6)2, [(bpy)2Ru(dpp)PtCl2](PF6)2, and [{(bpy)2Ru(dpp)}2RhCl2](PF6)5 supramolecular complexes with enantiopure light absorbing subunits. The design of the supramolecular architecture and intrinsic properties of each subunit contribute to the function of these systems. The careful design, synthesis and purification, thorough characterizations, and experimentation have led to deeper understanding of the molecular properties required for efficient H2O reduction. / Ph. D.