Novel Conjugated s-Tetrazine Derivatives Bearing a 4 H-1,2,4-Triazole Scaffold: Synthesis and Luminescent Properties

Abstract

A series of new symmetrical s-tetrazine derivatives, coupled via a 1,4-phenylene linkage with a 4H-1,2,4-triazole ring, were obtained. The combination of these two rings in an extensively coupled system has significant potential applications, mainly in optoelectronics. The methodology used turned out to be useful regardless of the type of five-membered ring or the nature of the individual substituents. All the products were identified by spectroscopic methods, and the target compounds were tested for luminescent properties. This study showed that all the synthesized highly-conjugated triazoles exhibited luminescence; in particular, one derivative, 3,6-bis(4-(5-(4-methoxyphenyl)-4-phenyl-4H-1,2,4-triazol-3-yl)phenyl)-1,2,4,5-tetrazine (13b), showed strong fluorescence emission and ahigh quantum yield close to 1.

Keywords: 4H-1,2,4-triazole; Pinner reaction; s-tetrazine.

Scheme 1

Synthesis of imidoyl chlorides (6a–d) and 1,3,4-oxadiazoles (7a–d).

Scheme 2

Synthesis of precursors containing a 4H-1,2,4-triazole ring (9a–h).

Scheme 3

Synthesis of s-tetrazine derivatives coupled via a 1,4-phenylene linkage with a 4H-1,2,4-triazole ring (13a–h).