Peralkynylated Tetraazaacene Derivatives

Abstract

The synthesis of ad ecaethynylated tetraazapentacene is described. It was obtained by ac ombination of condensation reactions giving the two pyraziner ings and subsequentc onsecutive Stille-type couplings. This is the first example of any higher (hetero)acene that is peralkynylated. The presence of the four nitrogen atomsr emoves the peri interaction of the substituted alkyne groups, giving this rock-stable and highly twisted heteroacene.Herein, we disclose the synthesis of an octaalkynylated tetraazatetracene and ad ecaalkynylated tetraazapentacene. Peralkynylated representatives are known of some aromatic systems;t he first ever described was Vollhardt's hexaethynylbenzene, prepared from hexabromobenzene and TMS acetylene in as ixfold Sonogashira reaction. [1] Later,t etraethynylethylenes were prepared by Hopf and co-workers [2] and by Diederich and co-workers, [3] followed by tetraalkynylated cyclobutadiene complexes achieved by Bunz and co-workers [4] as wella sp eralkynylated cyclopentadienyl species either as radical (Rubin) [5] or stabilized as cymantrene or ferrocene. [6] However,f or larger aromatic systems, such as naphthalene or anthracene, peralkynylated species are unknown-attempts of alkynylation lead to annulation reactions due to severe peri interactions of the alkynes-yet ap eralkenylated naphthalene has been prepared by de Meijere and co-workers. [7] To solve this issue, the offending peri interactions will have to be removedb ys ubstitution of aC -CC-R-group throughanitrogen. As ac onsequence, peralkynylated phenazine and quinoxaline are known. [8] However,none of the larger peralkynylated N-heteroacenes have ever been prepared. Herein, we disclose the synthesis of the higher homologues, ap eralkynylated tetraazatetracene and tetraazapentacene derivative.Startingf rom diamine 1, [9] reaction with tetrabromoorthoquinone under acidic conditions furnished the thiadiazole 2, which, uponS tille reaction with the stannylated acetylenes followed by MnO 2 oxidation of the intermediate N,N'-dihydrocompound, gave the hexaethynylated phenazinthiadiazoles 3a and b (Scheme 1). Attempts to open the thiadiazole ring with LiAlH 4 resultedinl ow yields, with zinc in acetic acid lead to de-Scheme1.Synthesis of the peralkynylated tetraazaacenes 6 and 8 (top) and structure of TIPSTAP [10] for comparison (bottom).

Exploring the potential of tetraazaacene derivatives as photovoltaic materials with enhanced photovoltaic parameters

“…Our reference molecule has computed HOMO and LUMO values −5.67 and −3.57 eV, respectively, while the experimental HOMO and LUMO values for the reference molecule are −5.57 and −3.72 eV, respectively [23]. M1–M4 have HOMO energy levels −6.05, −6.40, −6.12, and −5.99 eV, respectively.…”

“…The absorption value of R in the UV/visible spectrum with functionals MPW1PW91, CAM B3LYP, B3LYP, and WB97XD are 756, 615, 793, and 607 nm respectively as shown in Figure 2. After careful analysis, CAM‐B3LYP is selected for simulation of the UV/visible spectra of our representative compound R because the reported experimental value of reference R (651 nm) [23] is in close agreement with the calculated value along with CAM‐B3LYP/6‐31G++(d,p). Hence, for calculations of our designed molecules, CAM‐B3LYP/6‐31G++(d,p) has been chosen.…”

“…The designed molecules showed excellent photovoltaic properties. M1–M4 are matched with a renowned representative compound R [23].…”

Pyrazinacene conjugated polymers: a breakthrough in synthesis and unraveling the conjugation continuum

“…With this in mind, 11 was subjected to various Sonogashira cross-coupling reaction conditions with trimethylsilylacetylene, which were unsuccessful (Table S1 †). The Bunz 48,49 group have previously used Stille cross-coupling reactions to derivatize azaacenes. Taking cues from their work, 11 was subjected to Stille cross-coupling reaction with two alkynyl stannyl derivatives (R: t-Bu; Ph) in the presence of bis(benzonitrile)palladium(II) dichloride and P(t-Bu) 3 (Scheme 1).…”