<p> In the past, we have demonstrated that 1,8-anthraquinone-18-crown-5 (1) and its heterocyclic derivatives act as luminescent hosts for a variety of cations of environmental and clinical concern. We report here a series of heteroatom-substituted macrocycles containing an anthraquinone moiety as a fluorescent signaling unit and a cyclic polyheteroether chain as the receptor. Sulfur, selenium, and tellurium derivatives of 1,8-anthraquinone-18-crown-5 (<b>1</b>) were synthesized by reacting sodium sulfide (Na₂S), sodium selenide (Na₂Se) and sodium telluride (Na₂Te) with 1,8-bis(2-bromoethylethyleneoxy)anthracene - 9,10-dione in a 1:1 ratio (<b>2,3,</b> and <b>6</b>). These sensors bind metal ions in a 1:1 ratio (<b>7</b> and <b>8</b>), and the optical properties of the new complexes were examined and the sulfur and selenium analogues show that selectivity for Pb(II) is markedly improved as compared to the oxygen analogue <b>1</b> which was competitive for Ca(II) ion. </p><p> Selective reduction of <b>1</b> yields secondary alcohols where either one or both of the anthraquinone carbonyl groups has been reduced (<b> 15</b> and <b>9</b>). A new mechanism for the fluorescence detection of metal cations in solution is introduced involving a unique keto-enol tautomerization. Reduction of <b>1</b> yields the doubly reduced secondary alcohol, <b> 9. 9</b> acts as a chemodosimeter for Al(III) ion producing a strong blue emission due to the formation of the anthracene fluorophore, <b>10,</b> via dehydration of the internal secondary alcohol in DMSO/aqueous solution. The enol form is not the most thermodynamically stable form under these conditions however, and slowly converts to the keto form <b>11.</b> </p><p> Currently we are focusing on cucurbituril derivatives, also described as molecular clips due to their folded geometry used as molecular recognition hosts. We first investigated the synthesis and characterization of aromatic methoxy/catechol terminated cucurbituril units that act as hosts for small solvent molecules, such as CH₂Cl₂, CH₃CN, DMF, and MeOH, through dual pi&hellip;H-C T-shaped interactions. We have calculated the single-point interaction energies of these non-covalent interactions and compared them to the dihedral angle formed from the molecular clip. We have also synthesized a molecular clip that contains terminal chelating phenanthroline ligands. This tetradentate ligand shows 2:3 metal:ligand binding with Fe(II) and 1:2 metal:ligand binding with Co(II) and Ni(II) cations.</p><p>

The integration of non-covalent interactions in materials provides a direct mechanism to customize materials properties to specific applications and create novel nanostructures. Combining self-assembly with non-covalent interactions serves as a powerful tool in the creation of complex macromolecular structures with thermodynamically reversible contacts. With a host of non-covalent interactions available (e.g. dative bonding, hydrogen bonding, electrostatic pairings, π-stacking), tailoring the size and stability of self-assembled materials can be achieved through choice of interaction. This thesis describes two distinctive areas of research employing a rational combination of self-assembly and non-covalent interactions: (1) the synthesis and self-assembly of recognition unit functionalized Polyhedral Oligomeric Silsesquioxane (POSS) units and (2) the study of redox-modulated, molecular recognition in macromolecular systems. POSS units have long been employed as covalent additives in both polymeric and ceramic-based systems. Now, they have found alternative uses as non-covalent modifiers in multiple supramolecular systems. POSS units inherently feature a variety of attributes, which make them attractive as molecular recognition elements. These three-dimensional, nanoscale "building blocks" (∼0.6 nm inner silicate core) can easily be functionalized with a variety of recognition units. Through synthetic modification we were able to create a versatile component for non-covalent self-assembly with defined spacial orientations. To that end, recognition unit functionalized POSS units have been shown to serve as potent non-covalent modifiers for applications including surface modification, nanoparticle self-assembly, thermal enhancement in polymeric systems, and potential cellular delivery systems. Modulating non-covalent interactions via the reduction or oxidation of a molecule serves as an effective means in tuning the formation of supramolecular assemblies. Initial solution-based studies of both non-specific (urea-quinone) and specific, three-point (flavin-diamidopyridine) hydrogen bonding systems have been successful in understanding the complex behaviors, which govern redox-modulated molecular recognition. This understanding led to the incorporation of electrochemically tunable "host-guest" interactions on polymers and surfaces. Several interesting behaviors ranging from reversible redox-modulated recognition to induced proton transfer processes were observed and the ongoing focus of this research seeks to combine materials applications and redox-modulated recognition to create responsive, electrochemically tunable polymers and surfaces.

This dissertation focuses on the fundamental understanding of the proton transfer process and translating the knowledge into design/development of new organic materials for efficient non-aqueous proton transport. For example, what controls the shuttling of a proton between two basic sites? a) Distance between two groups? or b) the basicity? c) What is the impact of protonation on molecular conformation when the basic sites are attached to rigid scaffolds? For this purpose, we developed several tunable proton sponges and studied proton transfer in these scaffolds theoretically as well as experimentally. Next we moved our attention to understand long-range proton conduction or proton transport. We introduced liquid crystalline (LC) proton conductor based on triphenylene molecule and established that activation energy barrier for proton transport is lower in the LC phase compared to the crystalline phase. Furthermore, we investigated the impact of several critical factors: the choice of the proton transferring groups, mobility of the charge carriers, intrinsic vs. extrinsic charge carrier concentrations and the molecular architectures on long-range proton transport. The outcome of this research will lead to a deeper understanding of non-aqueous proton transfer process and aid the design of next generation proton exchange membrane (PEM) for fuel cell.

Synthesis and magneto-structural characterization of hydrogen bonded organic nitronylnitroxide and verdazyl radicals were done. 35diMeO–4OHPhNN displayed 1D antiferromagnetic interactions attributed to the chain contacts between radical NO groups. Benzimidazole-based verdazyl radicals 2BImverd, and 5BImverd did not give diffraction quality crystals and were only characterized by EPR. The analogues 2BImisoverd and 5BImisoverd both gave x-ray diffraction quality single crystals that displayed formation of hydrogen bonded chains through the imidazole moieties. The magnetic susceptibility results indicated the presence of weak 1D AFM interactions for both radicals. The weakness of interactions was attributed to bulky isopropyl groups pushing the molecules apart and decreasing spin orbital overlap. A series of organic radical solid solutions (alloys) were made using BImNN and its fluorinated analogue F4BImNN. (F4BImNN)x(BImNN) (1−x) with x < 0.8 gave orthorhombic unit cells, while x > 0.88 gave monoclinic unit cells. (F4BImNN) (x)(BImNN)(1−x) (x = 0.1, 0.17, 0.25, 0.5, 0.75, 0.83, 0.9) displayed ferromagnetic interactions with J/k = (+)14–22 K, mainly controlled by hydrogen-bonded assembly of the radicals. Magnetic analysis over 0.4–300 K showed ordering behavior for all of these materials. The ordering temperatures of the orthorhombic samples increased linearly as (1−x) increased from 0.25 to 1.00. The variation was attributed to increased inter-chain distance as more F4BImNN was added into the orthorhombic lattice. The monoclinic samples were not part of the same trend, which was attributed to a change in the inter-chain arrangement. This was the very first study giving such complete magnetostructural detail linking ordering behavior to specific crystallographic features and intermolecular contacts. The magnetic behavior of F4BImNN was investigated at increased external pressures. The crystallographic c-axis (along which hydrogen bonds form) was compressed by 3% at 10 kbar and by 4% at 17.8 kbar. The overall lattice volume contracted by 12% from ambient pressure to 17.8 kbar. The magnetic susceptibility measured over 1.8–300 K showed an increase in ferromagnetic exchange interactions as pressure increased. The increase in exchange strength was attributed to pressure-increased overlap of spin orbitals in the hydrogen-bonded chains, which favored 1D ferromagnetic interaction. Electron paramagnetic resonance experiments on a single crystal of F4BImNN were also performed. The variation in g-value as a function of the crystal's position with respect to the applied magnetic field was investigated. The angular dependence of g was more pronounced at temperatures below 30 K. Pyrrole-based nitronylnitroxide radicals mNNPP, N–PN and 35NNPP were studied. mNNPP displayed formation of 1D chains with weak intra-chain FM interactions, N–PN gave 1D AFM interactions, and 35NNPP showed intramolecular FM and intermolecular AFM interactions.

The "push-pull" electronically substituted polymers poly(2 (5) -bromo-5 (2) -n-hexyloxy-1,4-phenylene vinylene), poly(2 (5) -chloro-5 (2) -n-hexyloxy-1,4-phenylene vinylene) and poly(2 (5) -fluoro-5 (2) -n-hexyloxy-1,4-phenylene vinylene) were synthesized by a soluble precursor method and were used to fabricate light emitting diode (LED) devices. Thermal elimination of the polyether precursors gives final conjugated polymers as flexible red films. Precursor polymers can be spin-cast from solutions onto indium/tin oxide (ITO) pretreated quartz plates, then thermally converted to the final red polymers. Light emitting diode fabrication is then completed by the thin film vapor deposition of calcium, followed by aluminum. LED devices of the "push-pull" polymers give light emission in the 620-635 nm range. Two fluorinated polymers, poly(2-fluoro-1,4-phenylene vinylene) and poly(2,5-difluoro-1,4-phenylene vinylene) were investigated for their electroluminescent (EL) properties. LED's using these materials as emissive layers show substantial EL wavelength shifts (560 nm and 600 nm, respectively) relative to emission from unsubstituted poly(1,4-phenylene vinylene) (565 nm). These differences in EL emission can be attributed to the electronic effects of fluorine substitution. Synthetic strategies were developed for copolymeric materials based on poly(1,4-phenylene vinylene). The alternating block copolymer, poly (1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene- 3,5-dimethoxy-1,4-phenylene) was synthesized by a modified Wittig polymerization utilizing trialkyl phosphonium salts. This resulted in a regiospecific trans-olefination reaction when compared to polymeric materials synthesized through the use of common triaryl-phosphonium salts. Harsh post-Wittig isomerization procedures using I$\sb2$ were bypassed as a result of the high trans-cis ratio of the final copolymer. It was fully characterized using the standard spectroscopic techniques as well as elemental analysis. Light-emitting single-layer diodes using the soluble, processible copolymer as the emitting layer gives green light with an electroluminescence maximum at 513 nm.

Seven nondisjoint dinitrenes were produced in order to determine the length of chain conjugation that would still allow effective inter-nitrene exchange communication. The dinitrenes were generated in frozen matrices of 2-methyltetrahydrofuran by photolysis of appropriate diazides by a 1000-Watt xenon arc lamp and studied by electron spin resonance (ESR) spectroscopy. Conjugation lengths varied from 17 to 29 atoms between spin sites. In each case, it was determined by variable temperature analysis that the high-spin quintet state was the ground state. Six other dinitrenes were also produced which surprisingly exhibited quintet state spectra at 77 K, despite having possible quinoid biradical resonance structures. Possible reasons for the latter observation include conformational torsion effects, combined with a preference to retain benzenoid sextet resonance structures. In addition to the molecules produced in this lab, numerous samples of mono-, di-, and tri-azidopyridines were jointly studied with Dr. Sergei Chapyshev of the Russian Institute of Chemical Physics. These systems were studied by ESR spectroscopy. The effect of the pyridine heteroatom upon the ESR spectroscopy of these systems was found to be considerable, relative to simpler aryl nitrenes. Several of the triazide of systems were deemed to be ground state septet systems.

Acylated aminopyridines provide models for specific flavoenzyme-cofactor interactions, allowing isolation and observation of the effects of hydrogen bonding on flavin NMR. To determine the relative hydrogen bond affinities of O(2) and O(4) of the flavin, a 2-aminopyridine based receptor was investigated. Additionally, this receptor allowed the effects of hydrogen bonding at O(2) and O(4) on the electron distribution in the flavin nucleus to be determined using $\sp{13}$C NMR. A new family of receptors for flavins based on 6-aryl-2,4-(acyldiamino)-s-triazines was synthesized. In these synthetic hosts, systematic variation of the spatially remote substituents on the 6-aryl ring altered the hydrogen bond donating abilities of the amide functionality and the hydrogen bond accepting properties of the triazine N(3). This variation resulted in a strong modulation of the efficiency of flavin binding, with association constants for the receptor flavin complexes ranging over an 8-fold range. In addition, the communication of electronic information over extended distances was also investigated. Polymers can provide relevant media for the modeling of biological processes, including molecular recognition. To explore this possibility, a diaminotriazine-functionalized polymer was synthesized, starting from Merrifield's peptide resin. This polymer selectively bound a flavin derivative through hydrogen bonding, efficiently extracting it from a chloroform solution, as monitored by UV-vis extraction studies. The temperature profile of this polymer-flavin binding was also investigated and compared to the analogous solution-phase triazine-flavin dyad. Hydrogen bonding and aromatic stacking are fundamental interactions in molecular recognition. These interactions are sensitive to the redox states of the components of the host-guest complex. To explore the interplay of recognition and redox processes, a system consisting of two hosts and one guest, where guest binding interactions (hydrogen bonding and aromatic stacking) were modulated via choice of redox state was examined. Proper choice of receptors then provided a device where the competition between the two hosts was controlled by the redox state of the guest. The efficient reversal of host preference in this assembly provided an electrochemically-controlled three-component, two-pole, molecular switch.

Magnetostructural investigations were carried out on pyrene-1-yl (Pyr) bearing nitronylnitroxide (NN) and iminoylnitroxide (IN) radicals. PyrNN gives two allotropes: one has spin-paired dyads with ΔE = J/k ≈ -178 K, and the other is only half spin-paired with ΔE = J/k ≈ -102 K and the other half paramagnetic. PyrIN also gives two allotropes, an anti conformation that is spin paired in the crystal lattice with ΔE = J/k = -410 K, and a syn conformation that is disordered and paramagnetic. PyrNN also was discovered to co-crystallize with C6F6 in 2:1 ratio to give chains of radical networks linked into networks exhibiting low dimensional 1-D or 2-D antiferromagnetic exchange behavior. Furthermore, PyrNN was discovered to form a 2:1:2 co-crystal with octafluoronaphthalene (OFN) and entrapped solvent dichloromethane (DCM), in which the radical is ``shepherded'' into forming chains of radical-radical contacts on the peripheries of (PyrNN-OFN-PyrNN)n pi-stacks, giving weak, low dimensional inter-radical antiferromagnetic (AFM) exchange interactions. Anthraquinone-substituted nitronylnitroxide radical (AntQNN) was synthesized and found to form two crystal polymorphs. Magnetostructural investigations carried on these indicated that both have antiferromagnetic (AFM) exchange behavior attributed to chain-type inter-radical contacts: one with J1D/k ≈ -3 K, and one with J1D/k ≈-17 K. Five different anthracene nitroxide-type biradicals were synthesized: 27AntdNN, 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Room temperature solution state, and frozen solution state electron spin resonance (ESR) studies were carried on all of these biradicals. Crystallographic packing information was successfully obtained for 27AntdIN, 26AntdNN, 26AntdIN, and 9Br27AntdNN. Magnetic susceptibility measurements were carried on 27AntdNN, 27AntdIN, 26AntdIN and 9Br27AntdNN. The NN derivatives showed both ferromagnetic (presumed intramolecular) and antiferromagnetic exchange interactions in the solid state. Four different anthraquinone nitroxide-type biradicals were synthesized: 27AntQdNN, 27AntQdIN, 26AntQdNN, 26AntdIN. ESR studies were carried on these biradicals, and showed that 27AntQdNN is not a stable organic radical. While ESR spectra confirmed that 27AntQdNN, 27AntQdIN are biradicals, ESR spectra with isolated monoradical behavior were obtained for 26AntQdNN, 26AntQdIN. Iodine substituted meta-phenylene nitroxide biradicals, IPhdNN, IPhNNIN, and IPhdIN were synthesized. Room temperature and frozen solution ESR studies showed triplet states with strong intramolecular spin interaction. Magnetic behavior and crystallography for IPhdIN (which incorporates DCM), showed halogen bonding between molecules that assists formation of chains between radical sites.