Synthesis and Reactivity of Dithienopyrazines**

Abstract

Heteroacenes developed to widely used building blocks in organic semiconductors for application in organic electronics due to their tunable structures and properties concomitant with inherent stability. Here, we report efficient preparation and investigation of so far unknown heterotriacenes, basic anti-and syn-dithienopyrazine 5 and 6. The comparison of the two isomers with respect to electronic properties and follow-up reactions gives insights into structure-property and -reactivity relationships. Examples of transition metal-catalyzed CÀ C crosscoupling reactions of corresponding halogenated derivatives show the practical impact for extended π-conjugated systems applied in optoelectronic devices.

Functional Dithienopyrazines – Structure-Property Relationships

“…Thus, for both, the '-disubstituted syn and anti-derivatives, a singlet for the H-3/3' protons of the DTPyz-core appears nearly invariant and in full accordance with those of parent DT-Pyzs 1 and 2 at = 7.52-7.55 ppm. [7] The singlet for the DTPyz-protons H-2/2' of the '-disubstituted derivatives is displaced to lower field at 7.91-7.92 ppm for directly arylated DTPyzs 7-9 and 13-15 and also coincide with parent DT-Pyzs 1 and 2, whereby those of ethynylated DTPyzs 17-19 and 20-22 are more deshielded (8.10-8.13 ppm) due to the electron-withdrawing character of the adjacent triple bonds. All in all, four series of structurally different TAA and TAA-ethynyl-substituted syn-and anti-DTPys were synthesized which should allow for the elaboration of subtle structure-property relationships.…”

“…hydrochloric acid (Avantor), tetrabutylammonium fluoride (Fluorochem), tri-tert-butylphosphine, Pd2(dba)3 (Sigma Aldrich), and Pd (PPh3)2Cl2 (TCI). 2,6-Dibromodithieno[2,3-b:3',2'-e]pyrazine 4, [7] 3, 5-dibromodithieno[2,3-b:3',2'-e]pyrazine 5, [7] 2,3, 5,6-tetrabromodithieno[2,3-b:3',2'-e]pyrazine 6, [7] 2,6-dibromodithieno[2,3-b:3',2'-e]pyrazine 10, [7] 3, 5-dibromodithieno[2,3-b:3',2'-e]pyrazine 11, [7] 2,3, 5,6-tetrabromodithieno[2,3-b:3',2'-e]pyrazine 12, [7] and 4-ethynyl-N,N-bis(4-methoxyphenyl)aniline 16, [11] were prepared according to literature procedures. were suspended in a mixture of water/THF (1:1) (5 mL) and degassed with argon for 1 h. Then, the catalytic system consisting of Pd2dba3 (21 mg, 0.02 mmol, 9 mol%) and HP(t-Bu)3BF4 (13 mg, 0.05 mmol, 22 mol%) were added and the reaction mixture was heated at 60 °C for 41 h. The chilled reaction solution was extracted with water and DCM.…”

“…In general, two distinct absorption bands are visible for each derivative: the more complex one at higher energies includes the absorption of the subchromophores, i.e., the TAA-unit at 300 nm [12] and the DTPyz core at 336 nm (syn) and 339 nm (anti) with their corresponding extinction coefficiency. [7] The band at lower energy can be assigned to a -* transition from the elongated -system with charge-transfer (CT) contribution due to the donor character of the peripheric TAA and the DTPyz acceptor core. The absorption is sensitive to the extent of conjugation in the long axis of the molecule and is found intensive for the ,'-and tetra-substituted representatives, but very much suppressed with low transition probability for the ,'-disubstituted ones.…”

“…[6] In comparison to BDTs, the energetic levels of their frontier orbitals, HOMO and LUMO, were stabilized by 0.7-0.8 eV each, rendering DTPyzs to rather electron-deficient and less oxidation-sensitive systems. [7] However, so far DTPyrzs were only very scarcely implemented into organic semiconductors. Rare examples are represented by Li et al, who synthesized and characterized a '-dithienyl-substituted DTPyz and showed successful application in photoconductive devices.…”

“…[9] In this communication, we now describe further development of DTPyz-based materials by functionalization of our basic syn-and anti-DTPyz 1 and 2 with triarylamine (TAA) units on the basis of elaborated procedures for efficient Pd-catalyzed C-C cross-coupling reactions of selectively brominated derivatives, which we originally developed for the syn-derivative. [7] In total, four different series of triarylamino-functionalized DTPyz derivatives 3-22 of the donor-acceptor-donor (D-A-D)-type were synthesized. Their optical and electrochemical characterization gave valuable structureproperty relationships allowing for application of DTPyzs as model for hole-transport materials (HTM) tailored for organic electronic devices such as, e.g., perovskite solar cells.…”