A convenient route to synthesize 1,2,4‐triazolo[1,5‐a]pyrimidine derivatives and their one and two‐photon absorption spectral properties

A convenient method for synthesizing α‐(1,2,4‐triazolo1,5‐a]pyrimidine‐2‐sulfonyl)methane derivatives, 3 and 4 , by the well known Knoevenagel reaction, in one step, is described. The two chromophores are stilbene‐type chromophores containing the same D‐π‐A structures and end‐capped with aromatic group as their donors. Measured with femtosecond multipass Ti:sapphire amplifier as irradiation source (pumped by the laser at 800 nm), the two chromophores show efficient two‐photon induced orange red fluorescence emission. The experimental results indicate that the numbers of branches of the two chromophores affect their one‐photon properties and two‐photon up‐conversion emission behaviors, and with the increasing numbers of branches, their wavelengths of λ^abs_max, λ^spf_max and λ^tpf_max exhibit bathochromic shifts.