The Pyrazinacenes

Abstract

Conspectus Pyrazinacenes are a class of nitrogen-containing heteroacene molecules composed of linearly fused pyrazine units, which might also include dihydropyrazine groups leading to different reduced states of the compounds. While they are structurally similar to hydrocarbon acenes (e.g., pentacene) the presence of increasing numbers of N-heteroatoms introduces several different additional features of the compounds so that they can be considered for investigations beyond those suggested for acenes (i.e., organic field-effect transistors, solar cell components). Pyrazinacenes are in several ways complementary to C–H-only acenes based on the increasing stability of reduced states of the compounds with increasing numbers of fused pyrazine rings, although an acene-like electronic structure persists in the compounds so far studied. However, the introduction of multiple N atoms leads to properties that depart from C–H-only acenes. In particular, the compounds exhibit a delocalization of NH protons in extended reduced compounds and oxidation state switchability in solution and at interfaces. The presence of NH groups also allows an easy introduction of solubilizing groups at the pyrazinacene chromophore. In this Account, we will describe the preparation of extended pyrazinacenes from dipyrazino­[2,3-b:2′,3′-e]­pyrazine (1,4,5,8,9,10-hexaazaanthracene; N6) derivatives up to 1,4,5,6,7,8,9,12,13,14,15,16,17,18-tetradecaazaheptacene (N14) and also assess structures of the relevant compounds based on X-ray crystallographic studies. Emergent properties of the molecules include highly unusual linear tautomeric processes based on a delocalization of protons (and the corresponding formation of orbitals based on multiple adjacent N lone electron pair interactions), which suggest special transport properties based on molecular protonics. Molecules such as decazapentacene (N10) exhibit multistability of oxidation state, and this is predicted to promote the redox catalytic properties of the compounds. The oxidation-state switching of on-surface processes is also described and has been investigated using scanning tunneling microscopy. The longest known pyrazinacene chromophore (N14) exhibits amphiprotism with its state of protonation being strongly coupled to its fluorescence emission properties in the near-infrared region indicating possible uses in pH-coupled bioimaging applications. The synthesis of the pyrazinacenes is flexible and allows the preparation of symmetrically or unsymmetrically substituted derivatives for the development of more complex molecules and for control of the electronic structure of the acene unit. Overall, the pyrazinacenes represent an emerging class of highly nitrogenous heteroacenes with unique properties and excellent potential for development in different applications based on their special supramolecular properties including guest binding or interactions in biological systems.

Structure and Electronics of a Series of CAAC-Stabilized Diboron-Doped Acenes from 1,4-Diboranaphthalene to 6,13-Diborapentacene

“…Doping of acenes with p-block heteroelements, mainly nitrogen and sulfur, has enabled access to significantly longer and more stable acene alternatives, ,− some of which exhibit multiple stable oxidation states. , Moreover, heteroacenes often present greater ease of functionalization, enabling fine-tuning of the material and optoelectronic properties and leading to a variety of applications, including OLED emitters, , OFET n-type semiconductors, , solar cell electron transporters, , and fluorescent biosensors. , …”

Mechanical Manipulation of Archimedean Spirals of an Achiral Pyrazinacene for Chiral Assemblies

“…The dynamic assembly process was monitored based on UV-vis absorption spectra of the monolayer films obtained at different surface pressures (Figure 4a). The UV-vis absorption spectrum of a solution (10 -6 m) of PA2 in chloroform contains well-resolved absorption bands at 391, 414, and 440 nm (Figure 4a), [18,19,32] which is highly characteristic of acene compounds. In spectra of the monolayer films, increasing surface pressure predictably leads to an increase in the absorbance intensity for the monolayer films, although the absorption peak positions are constant.…”

25 years of NICS - much more than nothing!

“…The convenience while applying (vide supra) is sure a very big advantage, especially in combination with a probe not altering the system. The other huge plus for NICS is the wide range of application in organic, [22][23][24][25][26][27][28][29][30] inorganic, [31][32][33][34][35] metal clusters, [36][37][38] carbon-materials, [39][40][41] supramolecular chemistry, [42][43][44][45] bio related chemistry, [46][47][48][49] porphyrine chemistry, [50][51][52][53] chemistry of taylor-made properties, 54 polymer chemistry 55,56 etc. and these topics can again be divided into sub topics, e.g., in organic chemistry like reaction mechanism with aromatic transition states, 8,57,58 Möbius- [59][60][61] and Craig-Möbius 62-65 aromatic systems, chelate systems 66 or to metalla aromatic systems, 65,[67][68]…”