Novel s-tetrazine-based dyes with enhanced two-photon absorption cross-section†
This paper reports the synthesis and the linear and non-linear absorption properties of a series of new tetrazine-based D–π–A–π–D and D–π–A type dyes. In these derivatives, a central tetrazine core was connected with one or two terminal triphenylamine moiety(ies) via various π-conjugated spacers. These compounds were efficiently synthesized by Stille or Suzuki–Miyaura cross-coupling as a key step. Their photophysical properties, including one-photon absorption and two-photon absorption (2PA), were investigated with special attention to structure–property relationships. Large 2PA cross-sections (>800 GM) of these tetrazine dyes were evaluated by open aperture z-scan and non-degenerate 2PA techniques. The strong 2PA of these molecules is attributed to the extended π system and to the enhanced intramolecular charge transfer between the triphenylamine donor and the center tetrazine acceptor.