Structural Modification, Polymerization and Applications of Boron Difluoride Formazanates

This thesis describes the synthesis and characterization of a new family of fluorescent and redox-active BF2 complexes of formazanate [R1-N-N=C(R3)-N=N-R5]− ligands. The complexes were easily synthesized in two high-yielding steps, from inexpensive starting materials and readily purified by conventional methods. The properties of the resulting complexes can be tuned through structural variation – for example, appending electron donating or withdrawing substituents, or extending π conjugation. These methods of structural variation can bathochromically or hypsochromically shift the maximum absorption and emission wavelengths, vary the quantum yields, and allow for tuning of the reduction potentials. Using these methods, the properties of these complexes were optimized for use as fluorescence cell-imaging agents, and efficient electrochemiluminescence emitters. In order to expand the scope of this chemistry, copper-assisted azide-alkyne cycloaddition (CuAAC) chemistry was used to further modify the BF2 formazanate scaffold. Using this method, benzyl groups were appended to the BF2 complexes, which showed that the reaction proceeded cleanly, and that the resulting products had red-shifted wavelengths of maximum absorption and emission, and increased fluorescence quantum yields. Using the same strategy, a tetraethylene glycol based azide imparted water solubility, and the resulting complex was used in fluorescence cell-imaging experiments. Additionally, ferrocene moieties could be appended, which quenched the fluorescence of the resulting complex. Upon oxidation of the ferrocene groups, the fluorescence was regenerated allowing for these compounds to be used as redox sensors. Finally, CuAAC was used to synthesize copolymers of BF2 formazanate complexes and 9,9-dihexylfluorene. The resulting polymers had low band gaps (Eg = 1.67 eV) and good film-forming properties, paving the way for their use in organic photovoltaics. Finally, reaction of an o-phenol-substituted formazan with BF3•OEt2 and NEt3 resulted in a complex reaction mixture, which contained 5 BN heterocycles with unprecedented connectivity and interesting optical and electronic properties. Two of the most unique complexes were selected, and their chemical reduction products – a stable anion, radical anion and diradical dianion were studied in detail. Combined, this work has opened up an entirely new area of molecular materials with application in a variety of fields. This thesis describes the details of the work described above

Boron Difluoride Formazanate Copolymers with 9,9-Di-n-hexylfluorene Prepared by Copper-Catalyzed Alkyne-Azide Cycloaddition Chemistry

The synthesis and characterization of copolymers based on boron difluoride formazanate (BF2L) and 9,9-di-n-hexylfluorene (hex2Fl) units are described. A series of model compounds [(BF2L)-(hex2Fl), (hex2Fl)-(BF2L)-(hex2Fl), and (BF2L)-(hex2Fl)-(BF2L)] were also studied in order to fully understand the spectroscopic properties of the title copolymer [(BF2L)-(hex2Fl)]n. The model compounds and copolymers, which were synthesized by copper catalyzed alkyne-azide cycloaddition chemistry, exhibited high molar absorptivities (25,700-54,900 M-1 cm-1), large Stokes shifts (123-143 nm, 3590-3880 cm-1), and tunable electrochemical behaviour (E°red1 ca. -0.75 V and E°red2 ca. -1.86 V vs. ferrocene/ferrocenium). The low-energy wavelength of maximum absorption and emission of the model compounds red-shifted relative to the BF2L repeating unit by ca. 30 nm per triazole ring formed, to maximum values of 557 nm and 700 nm in DMF, respectively. The low-energy absorption and emission properties of the copolymer were consistent with the model compound bearing two triazole rings [(hex2Fl)-(BF2L)-(hex2Fl)] and were not dependant on copolymer molecular weight. However, the title copolymers may show promise as a light-harvesting material based on their thin-film optical band gap of 1.67 eV

Structurally Diverse Boron-Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron-nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N2O23− formazanate ligand with BF3­•OEt2 and NEt3. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV-vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography

Synthesis and Characterization of Conjugated/Cross-Conjugated Benzene-Bridged Boron Difluoride Formazanate Dimers

One of the most common strategies for the production of molecular materials with optical properties in the far-red/near-IR regions of the electromagnetic spectrum is their incorporation into dimeric architectures. In this paper, we describe the synthesis and characterization (1H, 11B, 13C and 19F NMR spectroscopy, IR and UV-Vis absorption and emission spectroscopy, mass spectrometry and X-ray crystallography) of the first examples of boron difluoride (BF2) formazanate dimers. Specifically, the properties of meta- and para-substituted benzene-bridged dimers p-10 and m-10 were compared to closely related boron difluoride triphenyl formazanate complex 11 in order to assess the effect of electronic conjugation and cross conjugation on their light absorption/emission and electrochemical properties. While the properties of cross-conjugated dimer m-10 did not differ significantly from those of monomer 11, conjugated dimer p-10 exhibited red-shifted absorption and emission maxima and was easier to reduce electrochemically to its bis radical anion and bis dianion form compared to monomer 11. Both dimers are weakly emissive in the far-red/near-IR and exhibited large Stokes shifts (\u3e 110 nm, 3318 cm−1). Unlike a closely related para-substituted benzene-bridged boron dipyrromethene (BODIPY) dimer, the emission quantum yields measured for the BF2 formazanate dimers exceeded those observed for monomeric analogues

Boron Difluoride Adducts of a Flexidentate Pyridine-Substituted Formazanate Ligand: Property Modulation via Protonation and Coordination Chemistry

The synthesis and characterization of a flexidentate pyridine-substituted formazanate ligand and its boron difluoride adducts, formed via two different coordination modes of the title ligand, are described. The first adduct adopted a structure that was typical of other boron difluoride adducts of triarylformazanate ligands and contained a free pyridine subsituent, while the second was formed via chelation of nitrogen atoms from the formazanate backbone and the pyridine substituent. Stepwise protonation of the pydridine-functionalized adduct, which is essentially non-emissive, resulted in a significant increase in the fluorescence quantum yield up to a maximum of 18%, prompting study of this adduct as a pH sensor. The coordination chemistry of each adduct was explored through reactions with nickel(II) bromide [NiBr2(CH3CN)2], triflate [Ni(OTf)2] and 1,1,1,4,4,4-hexafluoroacetylacetonate [Ni(hfac)2(H2O)2] salts. Coordination to nickel(II) ions altered the physical properties of the boron difluoride formazanate adducts, including red-shifted absorption maxima and less negative reduction potentials. Together, these studies have demonstrated that the physical and electronic properties of boron difluoride adducts of formazanate ligands can be readily modulated through protonation and coordination chemistry

Side-Chain Boron Difluoride Formazanate Polymers via Ring-Opening Metathesis Polymerization

The synthesis, characterization, and ring-opening methathesis polymerization (ROMP) of a novel norbornene-based boron difluoride (BF2) formazante monomer are described in detail. The polymerization studies confirmed ROMP to occur in the presence of BF2 formazanates, and also demonstrated the controlled nature of the polymerization. The polymers retained many of the unique characteristics of the monomers in dichloromethane, including absorption and emission at maximum wavelengths of 518 and 645 nm, large Stoke\u27s shifts (uST = 127 nm, 3,800 cm-1), and the ability to act as electron reservoirs to form borataverdazyl-based poly(radical anions) (E°red1 = -0.95 V). Furthermore, the results described in this paper demonstrate the potential of these and related polymers based on BF2 formazanates as redox-active, light-harvesting materials

Evaluation of Anisole-Substituted Boron Difluoride Formazanate Complexes for Fluorescence Cell Imaging

The evaluation of three subclasses of boron difluoride formazanate complexes bearing o-, m-, and p-anisole N-aryl substituents (Ar) as readily accessible alternatives to boron dipyrromethene (BODIPY) dyes for cell imaging applications is described. While the wavelengths of maximum absorption (lmax) and emission (lem) observed for each subclass of complexes, which differed by their carbon-bound substituents (R), were similar, the emission quantum yields for 7a-c (R = cyano) were enhanced relative to 8a-c (R = nitro) and 9a-c (R = phenyl). Complexes 7a-c and 8a-c were also significantly easier to reduce electrochemically to their radical anion and dianion forms compared to 9a-c. Within each subclass, the o-substituted derivatives were more difficult to reduce, had shorter lmax and lem, and lower emission quantum yields than the p-substituted analogs as a result of sterically-driven twisting of the N-aryl substituents and a decrease in the degree of p conjugation. The m-substituted complexes were the least difficult to reduce and possessed intermediate lmax,lem,and quantum yields. The complexes studied also exhibited large Stokes shifts (82-152 nm, 2143-5483 cm-1). Finally, the utility of complex 7c (Ar = p-anisole, R = cyano), which can be prepared for just a few dollars per gram, for fluorescence cell imaging was demonstrated. The use of 7c and 4\u27,6-diamino-2-phenylindole (DAPI) allowed for simultaneous imaging of the cytoplasm and nucleus of mouse fibroblast cells

An Azide-Functionalized Nitronyl Nitroxide Radical: Synthesis, Characterization and Staudinger-Bertozzi Ligation Reactivity

An azide-functionalized nitronyl nitroxide was successfully synthesized and its reactivity towards the Staudinger-Bertozzi ligation was explored. While a model reaction in solution showed the conversion of the nitronyl nitroxide to an imino nitroxide radical, the same reaction at the interface of gold nanoparticles allowed for successful covalent incorporation of the nitronyl nitroxide radical onto the nanoparticles

A π-conjugated inorganic polymer constructed from boron difluoride formazanates and platinum(II) diynes

The first example of a π-conjugated polymer incorporating boron difluoride (BF2) formazanates is introduced. The film-forming properties, controllable reduction chemistry, and low optical band gap (ca. 1.4 eV) of the polymer make it an excellent candidate for use as a light-harvesting n-type semiconductor in organic electronics. Comparison of the polymer to model compounds confirmed that its unique optoelectronic properties can be directly attributed to the presence of the BF2 formazanate repeat unit and that the [Pt(PBu3)2]2+ unit must also be present to achieve the narrow band gaps observed

Synthesis and Characterization of a Family of Air-Stable Ferrocene- and Ruthenocene-Containing Primary, Secondary, and Tertiary Phosphines

The synthesis and characterization of a family of air-stable primary, secondary, and tertiary phosphines containing all possible combinations of ethylferrocene and ethylruthenocene substituents are reported. Each phosphine was characterized by 1H, 13C, and 31P NMR spectroscopy, IR and UV-vis absorption spectroscopy, mass spectrometry, and elemental analysis. With the exception of primary ethylruthenocene phosphine 8a, all of the title compounds have been studied by single crystal X-ray crystallography. Ferrocene-containing phosphines showed maximum absorption at wavelengths of ca. 440 nm and qualitatively reversible oxidation waves in their cyclic voltammograms with intensities scaling to the number of ferrocene units present. The average metal-cyclopentadienyl centroid distances observed for ferrocene-containing phosphines were shorter than those of ruthenocene-containing phosphines, which also had maximum absorption wavelengths of ca. 320 nm and underwent irreversible electrochemical oxidation. Phosphines containing both ethylferrocene and ethylruthenocene substituents displayed properties consistent with the presence of both metallocene types