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My research has demonstrated the feasibility of the experimental methodologies for proton-sensitive molecular probes of proton transport at the single-molecule level where a single molecule fluorescence spectral shift was observed in poly acrylamide gel (PAAG) matrix after the addition of HCl with a grating spectrometer. Proton-sensitive molecular probes are employed for observing variations of photophysical properties as protons from acid sources transport and react with the reporter molecules such as Coumarin 6 where it has two different protonated states and then shows distinguished emission spectrum. As well, in order to understand the fluorescence properties of neutral and protonated Coumarin 6 in each emission spectrum region, dual-channel detection experiment was built where those fluorescence emission spectrum are allowed to be separated into each optical detection channel. The two-color detection will provide us with the understanding of the heterogeneities indicative of the interaction of pH-responsive probe with its environment. Based on those methodologies and results, this research will lead to investigate how proton transfer kinetics and dynamics are influenced by the geometric arrangements such as inter-functional group spacing, alignment, and flexibility in single macromolecular scaffolds which will suggest the development for future fuel cell and better understanding of biological process.

Single-molecule magnets (SMMs) have been lauded for their application in next generation devices for their enhanced information storage capabilities, increased processing speeds, and increased storage densities compared to bulk magnets. However, the success of SMMs in such applications and their technological readiness is hindered by their operation temperatures and memory lifetimes. SMMs are molecular species that possess a bistable ground state and magnetic anisotropy, which together result in an energy barrier to the reorientation of the magnetic moment. The magnetic memory response relies on its ability to retain magnetization in the absence of an external field. To this end, lanthanide ions with their large inherent magnetic anisotropy combined with well-defined crystal field microstates are attractive candidates for eliciting higher operation temperatures and lifetimes. This dissertation focuses on the use of lanthanide ions in the development of high barrier SMMs with a close emphasis on the magnetic anisotropy and crystal field manipulation through geometry, design, and modification. In the pursuit of lanthanide (Ln)-based SMMs, two cyclooctatetraenyl (COT2-) complexes of the non-Kramers ion, TmIII, [TmIII(η8-COT)I(THF)2] and [K(18-C-6)(THF)2][TmIII(η8-COT)2], were isolated. As an ion that possess an integer angular momentum projection (J = 6), it was vital that a highly symmetric local environment was utilized to observe field-induced slow magnetic relaxation. The static and dynamic properties of TmIII(η8-COT)I(THF)2] and [K(18-C-6)(THF)2][TmIII(η8-COT)2] were characterized revealing Ueff of 7.93 K and 53.3 K, respectively. More importantly, the effect of increased symmetry was observed on the rate of quantum tunneling of the magnetization (QTM), where the rate was two orders of magnitude faster in the heteroleptic complex. This emphasized the importance of local symmetry for non-Kramers ions and contributed to the rare class of TmIII SMMs. Due to the prevalent role of QTM in Ln-based SMMs, a common strategy is to induce magnetic communication between Ln ions to overcome its detrimental effects. To this end, bridging units should be sufficiently small enough to bring the Ln ions close in proximity, yet the surrounding environment of the metal center should still promote uniaxial magnetic anisotropy. We compared the effect of ancillary ligands on the magnetic properties of two dinuclear DyIII compounds with the same {μ-Cl}2 core bridge. The complexes [DyIII{N(SiMe3)2}2(μ-Cl)(THF)]2 and [DyIII(η8-COT)(μ-Cl)(THF)]2 were characterized with static and dynamic magnetic measurements. The well-matched ligand field of the silyl amide ligands with the DyIII ion, precluded the observation of zero field tunneling. While both complexes are characterized by antiferromagnetic coupling, it is evident that peripheral ligands also play a vital role in determining the performance of multinuclear SMMs. Magnetic coupling between 4f centers is classically weak; however, the use of ligands with diffuse electron clouds may penetrate the shielded 4f orbitals to effectively promote communication. One such ligand that had not previously been investigated for its ability to couple the magnetic moment of Ln ions was the trianionic cycloheptatrienyl. Utilizing Ln silyl amides, in situ deprotonation afforded the dinuclear complexes [KLnIII2(η7-C7H7){N(SiMe3)2}4] (Ln = GdIII, DyIII, ErIII). The static and dynamic magnetic characterization revealed rare and highly sought-after ferromagnetic coupling in a Ln-based system. The ancillary silyl amide ligands were a necessity for the isolation of these dinuclear species yet did not provide a synergistic ligand field for the Ln ions when combined with the cycloheptatrienyl bridge, ultimately preventing the observation of slow relaxation in some of the variants studied. Pseudo-linear complexes, those molecules with strong axial donors have shown immense promise in the design of highly efficient SMMs. Our work has shown that amides are effective in directing the anisotropy of the Ln ions, thus the removal of the central organometallic bridge from the previous compounds would effectively create a highly anisotropic complex. This was achieved in our study of a formally five-coordinate complex of a ferrocene diamide ligated DyIII ion, [(NNTBS)DyIIII(THF)2]. The static and dynamic magnetic properties were characterized, yielding Ueff = 771 K with open magnetization hysteresis loops at zero-field, due in part to the axial disposition of the nitrogen atoms of the diamide ligand. Computational analysis of the parent compound and its fragments was completed. Our results indicated that the presence of equatorially coordinated solvent molecules such as THF, influence the axiality in the crystal field microstates more significantly than the coordinated halide. The removal of coordinated solvent such as THF, is imperative to improve the performance of DyIII SMMs. By way of a bulky bisanilide ligand that precludes the approach of solvent to the metal center, combined with a large bite angle, [K(DME)n][LArDyIII(X)2], a formally four coordinate complex, was investigated. In contrast to the complex of the ferrocene diamide ligand, retention of the magnetic moment was not observed at zero-field, despite the fact that the slow relaxation dynamics occurred over a greater temperature range for which Ueff = 1278-1334 K. In addition, variants of the bound halide (X = Cl, I) were examined for their effect on the static and dynamic magnetic properties, revealing zero field relaxation times that were on average 5.6x longer for the heavier congener. The collective results of the findings presented herein are being utilized to synthesize new low-coordinate Ln-based SMMs. Combining divalent and redox chemistries with bulky amido ligands will ideally elicit even larger energy barriers to spin reversal and higher blocking temperatures, supporting the push towards Ln-based SMMs with increased technological readiness.

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Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking suppression in single CdSe-OPV is linked to the degree of OPV coverage (inferred from AFM height scans) on the quantum dot surface. The effect of the complex electronic environment presented by photoexcited OPV ligands on the excited state property of CdSe-OPV is measured with single photon counting and photon-pair correlation spectroscopy techniques. Time-tagged-time-resolved (TTTR) single photon counting measurements from individual CdSe-OPV nanostructures, show excited state lifetimes an order of magnitude shorter relative to conventional ZnS/CdSe quantum dots. Second-order intensity correlation measurements g(2)(τ) from individual CdSe-OPV nanostructures point to a weak multi-excitonic character with a strong wavelength dependent modulation depth. By tuning in and out of the absorption of the OPV ligands we observe changes in modulation depth from g(2)(0) ≈ 0.2 to 0.05 under 405 and 514 nm excitation respectively. Defocused images and polarization anisotropy measurements also reveal a well-defined linear dipole emission pattern in single CdSe-OPV nanostructures. These results provide new insights into to the mechanism behind the electronic interactions in composite quantum dot/conjugated organic composite systems at the single molecule level. The observed intensity flickering, blinking suppression and associated lifetime/count rate and antibunching behaviour is well explained by a Stark interaction model. Charge transfer from photo-excitation of the OPV ligands to the surface of the CdSe quantum dot core, mixes electron/holes states and lifts the degeneracy in the band edge bright exciton state, which induces a well define linear dipole behaviour in single CdSe-OPV nanostructures. The shift in the electron energies also affects Auger assisted hole trapping rates, suppress access to dark states and reduce the excited state lifetime.

In this thesis, I describe the first exploratory experimental efforts probing light-matter interactions of chiral systems at the single molecule level. The dissymmetric single molecule chiroptical response in both excitation and emission polarization has been studied for different diastereomeric forms of bridged triarylamine helicenes. Fluorescence excitation circular dichroism (FECD), measuring the dissymmetric absorption with respect to excitation polarization, reports on the response to excitation polarization. The magnitude and distribution of chiroptical single molecule responses suggest both surface and orientation effects play a significant role. Computational modeling done to calculate the dissymmetry for specific orientations supports orientational dependence. Using a defocused imaging technique, which can be used to obtain orientation information for linear dipoles, emission patterns were obtained that lacked bilateral symmetry. These emission patterns were simulated using a semi-classical model that closely approximated the lack of bilateral symmetry. Refinement of the model and additional experiments using oriented molecules will allow for direct correlation of orientation and dissymmetry which is important for understanding the heterogeneities in the single molecule responses. In addition, dissymmetry in emission polarization has been studied using a novel imaging technique resolving polarization components on a frame-by-frame basis. The research into the intersection of single molecule spectroscopy and chiroptics has given new insight into the role of solvation and local environment in chiroptical interactions and may be useful for understand chiral-based photonics and advancing new technologies.

<p> The relative acidities of some aryl germanes have been measured in liquid ammonia.</p> <p> The NMR spectra of phenyl silane and phenyl germane have been completely analysed and the chemical shifts shown to arise from the presence of an electric dipole in the molecule. The NMR spectrum of phenyl germyl anion was unambiguously assigned and partially analysed. The results are consistent with little delocalization of the negative charge from the Ge onto the ring.</p> <p> The vibrational spectra of the germyl anion have been observed and the geometry of the molecule estimated from a normal coordinate analysis of the data.</p> <p> The Raman spectrum of liquid ammonia-D3 has been measured and two bands in the Raman spectrum of liquid ammonia have been reassigned.</p> / Thesis / Doctor of Philosophy (PhD)

<p> The infrared and Raman spectra of cyanoacetylene and deuterocyanoacetylene have been measured and ground state vibrational energy levels have been obtained from the analysis of these spectra.</p> <p> Two band systems have been identified in the absorption spectrum of cyanoacetylene in the region 2700 - 2000 Å. Vibrational and rotational analyses have shown that the lower energy transition involves a non-linear planar upper state having A" symmetry. Approximate geometry of the molecule in the A" state has been determined.</p> <p> In the second electronic transition the upper state has been found to be linear. A vibrational analysis has been obtained on the basis of an electronically forbidden 1Δ<--- 1 Σ+ or 1 Σ- <--- 1 Σ+ transition, which is made allowed by vibronic interactions.</p> / Thesis / Doctor of Philosophy (PhD)

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