Phenothiazinophanes: Synthesis, Structure, and Intramolecular Electronic Communication

Stable and Fully-Oxidized Methylene-Bridged Macrocyclic Phenothiazine Polyradical Cations

Macrocyclic arenes represent one of the most important and intensively investigated entities in supramolecular chemistry. However, research on the redox activities of macrocyclic arenes, especially their isolable and crystalline polyradical analogues, has been rarely reported. Here, we present the synthesis, redox activity, and application of methylene-bridged macrocyclic phenothiazines, where polyradical cations are successfully isolated and unambiguously characterized for the first time. This research provides an effective method for preparing polyradical macrocycles, which expands the scope of investigation into macrocyclic arenes and their potential applications.

Multicomponent synthesis of chromophores – The one-pot approach to functional π-systems

Multicomponent reactions, conducted in a domino, sequential or consecutive fashion, have not only considerably enhanced synthetic efficiency as one-pot methodology, but they have also become an enabling tool for interdisciplinary research. The highly diversity-oriented nature of the synthetic concept allows accessing huge structural and functional space. Already some decades ago this has been recognized for life sciences, in particular, lead finding and exploration in pharma and agricultural chemistry. The quest for novel functional materials has also opened the field for diversity-oriented syntheses of functional π-systems, i.e. dyes for photonic and electronic applications based on their electronic properties. This review summarizes recent developments in MCR syntheses of functional chromophores highlighting syntheses following either the framework forming scaffold approach by establishing connectivity between chromophores or the chromogenic chromophore approach by de novo formation of chromophore of interest. Both approaches warrant rapid access to molecular functional π-systems, i.e. chromophores, fluorophores, and electrophores for various applications.

Size-dependent properties and unusual reactivity of novel nonplanar heterocycloarenes

The solution-phase synthesis of (hetero)cycloarenes with a well-defined size and geometric structure remains a challenging topic in organic chemistry and materials science. Herein, two novel nonplanar N,S-heterocycloarenes (PTZ1 and PTZ2) containing two/three alternate phenothiazine-co-phenanthrene units were conveniently synthesized. The smaller size heterocycloarene PTZ1 adopts a unique butterfly-shaped geometry and shows moderate supramolecular host–guest interactions with both fullerenes C₆₀ and C₇₀; whereas the higher homologue PTZ2 has a saddle-shaped conformation and demonstrates no obvious encapsulation with C₆₀ or C₇₀. Meanwhile, benefiting from the relatively ordered molecular packing, the thin film of PTZ1 behaved as a p-type semiconductor, while the more distorted PTZ2 does not display any field-effect characteristics. Particularly, upon the oxidation of heterocycloarene PTZ1 by Oxone, an unusual bis(sulfone-co-orthoquinone) product PTZ1-Oxi with an arc-shaped geometry is obtained and identified by single-crystal X-ray analysis. Our findings markedly expand the known chemistry of (hetero)cycloarenes and open a new path for their further functionalization.

Two novel fully fused heterocycloarenes consisting of nonplanar phenothiazine building units have been designed and successfully synthesized, which show size-dependent properties and unusual reactivity.

SET and HAT/PCET acid-mediated oxidation processes in helical shaped fused bis-phenothiazines

Helical shaped fused bis-phenothiazines 1-9 have been prepared and their red-ox behaviour quantitatively studied. Helicene radical cations (Hel.+ ) can be obtained either by UV-irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant. The reaction of hydroxy substituted helicenes 5-9 with peroxyl radicals (ROO. ) occurs with a 'classical' HAT process giving HelO. radicals with kinetics depending upon the substitution pattern of the aromatic rings. In the presence of acetic acid, a fast medium-promoted proton-coupled electron transfer (PCET) process takes place with formation of HelO. radicals possibly also via a helicene radical cation intermediate. Remarkably, also helicenes 1-4, lacking phenoxyl groups, in the presence of acetic acid react with peroxyl radicals through a medium-promoted PCET mechanism with formation of the radical cations Hel.+ . Along with the synthesis, EPR studies of radicals and radical cations, BDE of Hel-OH group (BDEOH ), and kinetic constants (kinh ) of the reactions with ROO. species of helicenes 1-9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds.

Crystallisation-enhanced bulk hole mobility in phenothiazine-based organic semiconductors

A series of three novel donor-acceptor systems based on C(3)-malononitrile-substituted phenothiazines was synthesised in good overall yields and their thermal, spectroscopic, and electrochemical properties were characterised. The compounds were prepared through a sequence of Ullmann-coupling, Vilsmeier-Haack formylation and Knoevenagel-condensation, followed by Suzuki-coupling reactions for introduction of aryl substitutents at C(7) position of the phenothiazine. The introduction of a donor unit at the C(7) position exhibited a weak impact on the optical and electrochemical characteristics of the compounds and led to amorphous films with bulk hole mobilities in the typical range reported for phenothiazines, despite the higher charge delocalisation as attested by computational studies. In contrast, highly ordered films were formed when using the C(7)-unsubstituted 3-malononitrile phenothiazine, exhibiting an outstanding mobility of 1 × 10⁻³ cm² V⁻¹ s⁻¹, the highest reported for this class of compounds. Computational conformational analysis of the new phenothizanes suggested that free rotation of the substitutents at the C(7) position suppresses the ordering of the system, thereby hampering suitable packing of the new materials needed for high charge carrier mobility.

Thiophene-forming one-pot synthesis of three thienyl-bridged oligophenothiazines and their electronic properties

The pseudo five-component Sonogashira-Glaser cyclization synthesis of symmetrically 2,5-diaryl-substituted thiophenes is excellently suited to access thienyl-bridged oligophenothiazines in a one-pot fashion. Three thienyl-bridged systems were intensively studied by UV-vis and fluorescence spectroscopy as well as by cyclic voltammetry. The oxidation proceeds with lower oxidation potentials and consistently reversible oxidations can be identified. The Stokes shifts are large and substantial fluorescence quantum yields can be measured. Computational chemistry indicates lowest energy conformers with sigmoidal and helical structure, similar to oligophenothiazines. TD-DFT and even semiempirical ZINDO calculations reproduce the trends of longest wavelengths absorption bands and allow the assignment of these transitions to possess largely charge-transfer character from the adjacent phenothiazinyl moieties to the central thienyl unit.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Selected synthetic strategies to cyclophanes

In this review we cover various approaches to meta- and paracyclophanes involving popular reactions. Generally, we have included a strategy where the reaction was used for assembling the cyclophane skeleton for further functionalization. In several instances, after the cyclophane is made several popular reactions are used and these are not covered here. We included various natural products related to cyclophanes. To keep the length of the review at a manageable level the literature related to orthocyclophanes was not included.

Thia-bridged triarylamine heterohelicene radical cations as redox-driven molecular switches

Remarkably stable radical cations as redox-driven molecular switches.

Synthesis and structure of new 3,7,10-substituted-phenothiazine derivatives

The synthesis of new 3,7-dibromophenothiazine derivatives bearing bromoalkyl, mercaptoalkyl and alkylthioacetate groups on the N atom at position 10 is reported. The Suzuki coupling reaction of one of these derivatives via the bromine atoms at positions 3 and 7 with bromothiophene derivatives is also discussed.