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A conjugated bis-benzimidazole chromophore is predicted to show absorptions in the near-infrared (NIR) region of the electromagnetic spectrum. However, there are no reports to-date of any NIR absorbing and emitting dyes that are based on a bis-benzimidazole structural backbone. This thesis reports recent advancements in the discovery and study of this new class of dyes. Following literature procedures, the syntheses of bis(benzimidazolyl)methane compounds are successful. An unexpected product isolated during the attempted oxidation of a bis(benzimidazolyl)methane compound using p-chloranil showed intense absorption in the NIR (λmax = 712 nm, ε = 14600 L·mol-1·cm-1), solubilities in polar solvents like methanol and water, and electrochemical activities. X-ray crystallography, mass spectrometry, and NMR spectroscopy confirmed the connectivity and structure of the product to contain a combination of quinone and benzimidazole moieties, which later revealed to be the core chromophore by computational studies. This unprecedented combination of moieties gave a chromophore that is predicted to absorb in the far-red even without substitution. Attempts to synthesize boron-based bis-imidazole dyes with N-methylation shed light on the feasibility of the design of such moiety. Considering the additional functionality that could be accessed through the methylation of the labile benzimidazole nitrogen atoms, N-methylated bis(benzimidazolyl)methane precursors were successfully synthesized and fully characterized. Attempts of the boron coordination showed promising signs, as the 1H, 11B, and 19F NMR spectra showed solid evidence of the successful isolation of the boron chelate. Computational studies of methyl, phenyl, and triazole-substituted boron chelate derivatives projected absorptions in the NIR region. Intense transitions are found to be based on frontier molecular orbitals and differ significantly among the derivatives, predicting substantial tunability of this type of dyes. / Graduate / 2022-02-18

This study focused on the preparation and characterization of new indigo diimine (Nindigo) derivatives as a new atropisomeric scaffold. Trans- and cis- indigo diimines were studied and structure-property relationships were investigated regarding N-C atropisomerism using variable temperature 1H NMR studies and density functional theory calculations. Neutral trans- and protonated cis-Nindigos were prepared featuring a variety of mono ortho-substituted aryl imine groups with varying levels of steric bulk. The neutral trans-Nindigo derivatives generally have smaller N-C rotational energy barriers than their protonated cis-congeners. This finding is consistent with the latter having closer proximity of the N-aryl groups to each other, leading to steric repulsions between the two groups. The N-C rotational energy barriers are substituent dependent; the N-C rotational energy barriers of mono ortho substituted trans-Nindigos were in the range of 6.0 – 16.4 kcal/mol and can be classified as predominantly “Class 1’ atropisomers as defined by LaPlante, while the mono ortho substituted protonated cis-Nindigo analogs have N-C rotational barriers between 12.3 – 25.5 kcal/mol and are classified as “Class 1” and “Class 2” atropisomers. The introduction of additional substituents onto the other ortho position of the aryl imine subunit has significant consequences for the N-C rotational energy barriers of both the neutral trans- and protonated cis-Nindigos making them stable, or close to being, ‘Class 3’ atropisomers, having N-C rotational energy barriers between 31.5 – 276.9 kcal/mol and 29.3 – 32.6 kcal/mol respectively. Recognizing that the protonation state induced trans- to cis-isomerization process could have significant consequences regarding the potential applicability of these atropisomeric Nindigo derivatives, cis-Nindigo derivatives were synthesized that contained a tether (oxalyl or palladium (II) acetylacetonate) between the two indole type nitrogens of the Nindigo, which prevent the central -C=C- from isomerizing. The N-C rotational barriers of the tethered cis-Nindigos also displayed substituent dependent N-C rotational energy barriers. The protonation state of the N, N’-oxalyl bridged cis-Nindigos has a significant impact (higher in energy by a minimum of 5.1 kcal/mol) on the N-C rotational barriers; the neutral N, N’-oxalyl bridged cis-Nindigos have N-C rotational energy barriers ranging between 11.8 – 14.9 kcal/mol, classifying them as “Class 1” atropisomers, while their protonated congeners have N-C rotational energy barriers between 16.9 – 19.8 kcal/mol, which classifies them as “Class 1” atropisomers but are on the cusp of being “Class 2” atropisomers. The size of the tether influences the N-C rotational energy barriers of cis-Nindigos; the one-atom bridged palladium (II) acetylacetonate complexes have generally lower N-C rotational energy barriers than their protonated N, N’-oxalyl bridged cis-Nindigo congeners. The palladium acetylacetonate tethered cis-Nindigo complexes displayed substituent N-C rotational energy barrier dependence and the mono ortho substituted analogs have N-C rotational energy barriers between 12.4 – 20.2 kcal/mol and are predominantly “Class 1” atropisomers, while the bulkier analogs are “Class 2” atropisomers. The palladium (II) acetylacetonate cis-Nindigo complexes that have aryl imine groups with a 2,6-disubstitution pattern have N-C rotational energy barriers greater than 19.7 and 20.2 kcal/mol and are presumed to be stable “Class 3” atropisomers like their unbridged neutral trans- and protonated cis-Nindigo counterparts. / Graduate / 2023-09-12