The Radical Anion and Dianion of Benzo[3,4]cyclobuta[1,2-b]phenazine.

We present the reduction of two azaacenes (a benzo-[3,4]cyclobuta[1,2-b]phenazine and a benzo[3,4]cyclobuta[1,2-b]naphtho[2,3-i]phenazine derivative), featuring a single cyclobutadiene unit, to their radical anions and dianions. The reduced species were produced using potassium naphthalenide in the presence of 18-crown-6 in THF. Crystal structures of the reduced representatives were obtained and their optoelectronic properties evaluated. Charging these 4n Hückel systems gives dianionic 4n + 2 π-electron systems with increased antiaromaticity, according to NICS(1.7)zz calculations, featuring unusually red-shifted absorption spectra.

Cyclopentannulated Dihydrotetraazapentacenes.

The transition-metal-catalyzed cyclization of bissilylethynylated N,N'-dihydrotetraazapentacene (TIPS-TAP-H2 ) into bissilylated cyclopenta[fg,qr]pentacenes is reported. Depending on the catalyst either none, one or two silyl groups migrate and change their positions in the formed five-membered rings. The optoelectronic properties are quite similar, whereas the packing motifs differ dramatically. Control experiments and quantum chemical calculations were performed to investigate the mechanism of the reaction and the selectivity of the silyl shift.

Multifunctional Magnetic Resonance Imaging Probes.

Magnetic resonance imaging is characterized by high spatial resolution and unsurpassed soft tissue discrimination. Development and characterization of both intrinsic and extrinsic magnetic resonance (MR) imaging probes in the last decade has further strengthened the pivotal role MR imaging holds in the assessment of cancer in preclinical and translational settings. Sophisticated chemical modifications of a variety of nanoparticulate probes hold the potential to deliver valuable multifunctional tools applicable in diagnostics and/or treatment in human oncology. MR imaging suffers from a lack of sensitivity achievable by, e.g., nuclear medicine imaging methods. Advantages of including additional functionality/functionalities in a probe suitable for MR imaging are thus numerous, comprising the addition of fundamentally different imaging information (diagnostics), drug delivery (therapy), or the combination of both (theranostics). In recent years, we have witnessed a plethora of preclinical multimodal or multifunctional imaging probes being published mainly as proof-of-principle studies, yet only a handful are readily applicable in clinical settings. This chapter summarizes recent innovations in the development of multifunctional MR imaging probes and discusses the suitability of these probes for clinical transfer.

Synthesis of Triptycene-Substituted Azapentacene and Azahexacene Derivatives.

We describe the synthesis and characterization of novel iptycene-substituted azaacenes by using either a classic condensation route (diamine plus ortho-quinone) and/or a Pd-catalyzed coupling of an aromatic diamine with an aromatic dihalide. The attachment of an iptycene unit leads to a significant blueshift (15 nm) in the UV/Vis spectra of these azaacenes. The iptycene unit stabilizes a hexaazahexacene with a λmax abs of 833 nm. By employing 5,6-diamino(benzothiadiazole) as a synthon for tetraaminobenzene, we could prepare the symmetrical bis-triptycene-substituted tetraazapentacene in high yields.

Synthesis of Alkynylated Benzo[a]naphtho[2,3-i]phenazine Derivatives.

Thermal condensation of 2,3-diamino-1,4-(bistriisopropylsilylethynyl)benzene, -naphthalene,-anthracene, and -benzothiadiazole substrates with 1,2-naphthalenedione forms bent benzophenazine-type heteroarenes in a one-step reaction in good to excellent yields. The targets are investigated by UV/Vis spectroscopy, cyclic voltammetry, and single-crystal X-ray crystallography. The packing of the targets in the solid state follows either a herringbone or a brick wall motif. In the case of 8,13-bis(triisopropylsilylethynyl)dibenzo[a,i]phenazine, polymorphs with either packing result.

A Stable Bis(benzocyclobutadiene)-Annelated Tetraazapentacene Derivative.

Biphenylene-2,3-dione is a powerful reagent to build up cyclobutadiene-containing azapolyheterocycles. The target structures are formed in high yields through classical condensation of suitable aromatic diamines with the biphenylenedione. To achieve the title compound, the biphenylenedione is coupled with a diaminobenzothiadiazole derivative. Reductive cleavage of the thiadiazole ring and subsequent condensation with the biphenylenedione gives the title compound in which a central tetraazapentacene is flanked by two benzocyclobutadiene units. This compound is stable despite its extended π-system and its optical features are blueshifted in comparison to those of the symmetrical tetraazapentacene.

The Radical Anion and Dianion of Tetraazapentacene.

The mono- and bis-reduction of 6,13-bis((triisopropylsilyl)ethynyl)quinoxalino[2,3-b]phenazine (1) with potassium anthracenide in THF is reported. Both the radical anion 1(.-) and the dianion 1(2-) were isolated and characterized by optical and structural (single-crystal X-ray diffraction) methods. Solutions of the radical anion 1(.-) were stable in air for several hours and characterized by EPR spectroscopy. Dianion 1(2-) is highly fluorescent and photostable.

Synthesis and characterization of biphenylene-containing diazaacenes.

We describe the efficient synthesis of substituted benzo[3,4]cyclobuta[1,2-b]phenazine, benzo[3,4]cyclobuta[1,2]benzo[1,2-i]phenazine, and benzo[3,4]cyclobuta[1,2-b]naphtho[2,3-i]phenazine by a condensation reaction of aromatic diamines with the stable biphenylene-2,3-dione.

Soluble diazaiptycenes: materials for solution-processed organic electronics.

The synthesis and characterization of soluble azaiptycenes is reported. Optical and physical properties were studied and compared with those of the structurally consanguine azaacenes. Electrochemical experiments and quantum-chemical calculations revealed the electronic structure of the iptycene derivatives. Their crystallization behavior was examined. A highly fluorescent amorphous diazatetracene derivative was integrated into a simple organic light-emitting diode, showing enhanced performance compared with that of previously reported, structurally similar tetracenes.

Microporous Triptycene-Based Affinity Materials on Quartz Crystal Microbalances for Tracing of Illicit Compounds.

Triptycene-based organic molecules of intrinsic microporosity (OMIMs) with extended functionalized π-surfaces are excellent materials for gas sorption and separation. In this study, the affinities of triptycene-based OMIM affinity materials on 195 MHz high-fundamental-frequency quartz crystal microbalances (HFF-QCMs) for hazardous and illicit compounds such as piperonal and (-)-norephedrine were determined. Both new and existing porous triptycene-based affinity materials were investigated, resulting in very high sensitivities and selectivities that could be applied for sensing purposes. Remarkable results were found for safrole - a starting material for illicit compounds such as ecstasy. A systematic approach highlights the effects of different size of π-surfaces of these affinity materials, allowing a classification of the properties that might be optimal for the design of future OMIM-based affinity materials.

Bisalkynylated 3,6-diiminocyclohexa-1,4-diene-1,4-diamine.

Reduction of bis(benzothiadiazol) by LiAlH4/CuI gives diethynylated diaminobenzoquinoneimine. This building block accesses novel targets in a one-step condensation reaction with different ortho-quinones, resulting in unexpected rearrangement products. The compounds are characterized by their photophysical and electrochemical data as well as quantum chemical calculations.