Synthesis of a tetrazine–quaterthiophene copolymer and its optical, structural and photovoltaic properties

Abstract

Herein, we report the synthesis of a novel, tetrazine-based conjugated polymer. Tetrazines have the benefit of being strong electron acceptors, while little steric hindrance is imposed on the flanking thiophene rings. Conversion of a suitably substituted nitrile precursor led to 3,6-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-1,2,4,5-tetrazine (2OD-TTz). Palladium-catalyzed copolymerization of 2OD-TTz with a bithiophene monomer yielded an alternating tetrazine–quaterthiophene copolymer (PTz4T-2OD). The polymer PTz4T-2OD showed an optical band gap of 1.8 eV, a deep HOMO energy level of − 5.58 eV and good solubility. In combination with the non-fullerene acceptor ITIC-F, solar cells with power conversion efficiencies of up to 2.6% were obtained. Electronic supplementary material The online version of this article (10.1007/s10853-019-03551-3) contains supplementary material, which is available to authorized users.

A pyrrolopyridazinedione-based copolymer for fullerene-free organic solar cells

“…The corresponding mass loss of 3% can be assigned to the loss of one equivalent of nitrogen per repeating unit. 24 Li et al reported a 90% yield for this reaction which was in line with our observation. 12 Compared to tetrazines, pyrrolopyridazine (PPD) monomers have an increased electron-deficient character and are furthermore more thermally stable than the respective tetrazines.…”

“…This allows for tuning the polymer properties, but at the cost of more synthetic effort for obtaining the required nitriles. Recently, we followed the approach of incorporating large branched alkyl side chains into the tetrazine based monomer and attempted to combine the necessity of the large alkyl chains with the benefit of an improved phase separation and domain purity in the absorber layer as exemplified by Liu et al 23,24 Combination of this tetrazinequaterthiophene copolymer with the NFA ITIC-F (3,9-…”

“…to an efficiency of 2.6%. 24 A similar polymer with a fluorine-substituted quaterthiophene sequence gave 5.1% efficiency which could be further improved to 7.9% by replacing the quaterthiophene sequence with a suitably substituted sexithiophene. 25 Nevertheless, tetrazine-containing polymers suffer from limited thermal stability, as demonstrated by us and others.…”

The inverse-electron demand Diels–Alder reaction of tetrazines with cyclic enol ethers

“…[23]. R f (CH 2 Cl 2 / MeOH 20/1) = 0.21; 1 H NMR (300 MHz, CDCl 3 , 25 °C): δ = 8.77-8.69 (m, 2H, py 3,6 ), 8.67 (d, 1H, 3 J HH = 5.0 Hz, py 6 ), 8.60 (s, 1H, pz 5 ), 8.30 (d, 1H, 3 J HH = 8.0 Hz, py 3 ), 7.97…”

“…Since the first report of the synthesis of pyridazines from tetrazines and alkenes, allenes, or alkynes by Carboni and Lindsey in 1959 [1], this reaction received ever increasing attention first because of its synthetic potential in heterocyclic chemistry [2] and later in chemical biology applications because particular tetrazine/olefin combinations provide exceptionally fast and selective ligation reactions at very low concentrations [3]. Additionally, applications in material chemistry evolved [4][5][6]. The mechanistic understanding of the inverse-electron demand Diels-Alder cycloaddition (iEDDA) reactions, the broader term for the reaction of a tetrazine with an olefin giving a pyridazine derivative, is well developed and nicely summarized in a recent review article [7].…”