Isomerization-Controlled Dual-State Emission of Pyridyl Triazolopyridine Derivatives

The high-yielding two-step reaction synthesis of pyridyl triazolopyridine derivatives 1a–1e with substituents in positions C7 and C2′ is reported. All derivatives show intense blue fluorescence emission with excellent ΦF in acidic solution (up to 72%) and in their neutral solid state (up to 66%). The experimental results together with the theoretical calculations suggest that the isomerization reaction is detrimental to the emissive properties of these compounds because it favors the non-radiative de-excitation via fast molecular motion.