Synthesis and Two-photon Absorption Properties of Multi-branched Pyrazine Derivatives

A series of multi-branched pyrazine derivatives with two, three and four branches have been synthesized. The linear absorption (peak position: 290 similar to 390 nm) and emission spectra (peak position: 400 similar to 510 nm) along with the two-photon excited fluorescence (TPEF) spectra (excited at 720 nm) showed regular red-shifts as the branch number increased, and the fluorescence quantum yields of the pyrazine derivatives increased (from 0.13 to 0.25). In addition, the two-photon absorption (TPA) cross section sigma non-linearly increased with a ratio of 1 : 2.8 : 3.7, which is near to the ratio of the square of branching number n(2) (1 : 2.25 : 4), indicating a remarkable cooperative enhancement of sigma in the multi-branched pyrazine derivatives. The sigma value of the four-branched compound is 1007 GM. It was also found that the ortho-/para-branching pattern took great advantage over the meta-branching pattern in the linear fluorescence and TPEF.