Synthesis and Characterization of a Trisheteroleptic RuII‐Based Molecular Switch

The synthesis of a trisheteroleptic ruthenium complex [Ru(tb)(dppz)(tmbiH₂)][PF₆]₂ (tb=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine, dppz=dipyrido[3,2‐a:2′,3′‐c]phenazin, tmbiH₂=5,6,5′,6′‐tetramethyl‐2,2′‐bibenzimidazole) is described. In addition, the structural characterisation by means of 1D, 2D ¹H NMR spectroscopy, and mass spectrometry, along with determination of the solid‐state structure of the important precursor Ru(tb)(dppz)Cl₂, supports the proposed octahedral coordination geometry. The capability of tmbiH₂ to form hydrogen bonds is corroborated by the solid‐state structure. The photochemical characteristics of this complex can be described as a combination of the “light switch” effects, which are either attributed to the dppz or to the tmbiH₂ ligand. To illustrate the molecule’s double switchable features, steady‐state absorption and emission measurements were performed, which include the determination of the quantum yield and the pK_a values of the acidic protons of the tmbiH₂ ligand. Notably, the emission lifetimes are sensitive to the solvents used. This phenomenon is due to a proton‐coupled deactivation of the excited metal‐to‐ligand charge transfer (MLCT) state of the complex.     

Solution polymerization of polybenzimidazole

Polybenzimidazoles (PBI) are an important class of heterocyclic polymers that exhibit high thermal and oxidative stabilities. The two dominant polymerization methods used for the synthesis of PBI are the melt/solid polymerization route and solution polymerization using polyphosphoric acid as the solvent. Both methods have been widely used to produce high‐molecular weight PBI, but also highlight the obvious absence of a practical organic solution‐based method of polymerization. This current work explores the synthesis of high‐molecular weight meta‐PBI in N,N‐dimethyl acetamide (DMAc). Initially, model compound studies examined the reactivity of small molecules with various chemical functionalities that could be used to produce 2‐phenyl‐benzimidazole in high yield with minimal side reactions. ¹H NMR and FTIR studies indicated that benzimidazoles could be efficiently synthesized in DMAc by reaction of an o‐diamine and the bisulfite adduct of an aromatic aldehyde. Polymerizations were conducted at various polymer concentrations (2‐26 wt % polymer) using difunctional monomers to optimize reaction conditions in DMAc which resulted in the preparation of high‐molecular weight m‐PBI (inherent viscosities up to 1.3 dL g^?1). TGA and DSC confirmed that m‐PBI produced via this route has comparable properties to that of commercial m‐PBI. This method is advantageous in that it not only allows for high‐polymer concentrations of m‐PBI to be synthesized directly and efficiently, but can be applied to the synthesis of many PBI derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1795–1802     

Facile synthesis of benzobisimidazole and bibenzimidazole-based bisnitriles as potential precursors for DNA minor groove binders

The synthesis of bisnitrile derivatives of benzobisimidazole and bibenzimidazole in a good yield is described in detail for the first time. Nucleophilic substitution of 1,5-difluoro-2,4-dinitrobenzene using different amines produced the intermediate diamines that were reduced using sodium borohydride/Pd(C) to produce the tetramines. These tetramines were allowed to couple with different aldehydes to produce the final benzimidazoles. In a different investigation, these bisnitrile derivatives will be used to make benzimidazole diamidines that could be used as potential mixed sequence minor groove binders.