Abstract
A safe and efficient synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine from the commercial diaminomaleonitrile is reported. Conditions for selective aromatic nucleophilic substitution of one or two bromine atoms by oxygen and nitrogen nucleophiles are found, whereas thiols formed the bis-derivatives only. Buchwald-Hartwig or Ullmann techniques are successful for incorporation of a weak nitrogen base, such as carbazole, into the [1,2,5]thiadiazolo[3,4-d]pyridazine core. The formation of rather stable S…η2-(N=N) bound chains in 4,7-bis(alkylthio)-[1,2,5]thiadiazolo[3,4-d]pyridines makes these compounds promising for the design of liquid crystals.
Highlights
Electron-deficient π-conjugated building blocks have been widely applied for the preparation of functional organic dyes and electronic materials [1,2,3]
The convenient and safe synthesis of dimethyl 1,2,5-thiadiazole-3,4-dicarboxylate from commercially available 2,3-diaminomaleodinitrile was proposed; this clears the way for large-scale preparation of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine
Buchwald-Hartwig or Ullmann reactions were successfully employed for the incorporation of a weak nitrogen substituent, e.g., carbazole, to the [1,2,5]thiadiazolo[3,4-d]pyridazine system
Summary
Electron-deficient π-conjugated building blocks have been widely applied for the preparation of functional organic dyes and electronic materials [1,2,3]. The choice of the acceptor is important for high performance of the materials. Electron-acceptor building blocks (A) should be linked with an at least one electronodonor (D) either directly or through a π-conjugated bridge (π) in small molecules or polymers. Many applications of these materials can be mentioned: dye-sensitized solar cells (DSSCs) [2,5,6], bulk heterojunction solar cells (BHJ) [7,8], n-type organic field-effect transistors [9,10], near infrared absorption and emissions materials [11,12], electrochromic materials [13,14], and many others
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