Donor-acceptor 1,2,4,5-Tetrazines Prepared by Buchwald-Hartwig Cross-Coupling Reaction and Their Photoluminescence Turn-on Property by Inverse Electron Demand Diels-Alder Reaction

A facile efficient synthetic tool, Buchwald-Hartwig cross-coupling reaction, for the functionalization of 1,2,4,5tetrazines is presented. Important factors affecting the Buchwald-Hartwig cross-coupling reaction have been optimized. Seven new donor-acceptor tetrazine molecules (TA1-TA7) were conveniently prepared in good to high yields (61%-72%). They have been subsequently engaged in inverse Electron Demand Diels-Alder (iEDDA) reaction with cyclooctyne. The photophysical and electrochemical properties of the new pyridazines have been studied. Some are fluorescent acting as turn-on probes. More importantly two pyridazines (DA3 and DA6) exhibit room temperature phosphorescence (RTP) properties.