Pyrazine luminogens with “free” and “locked” phenyl rings: Understanding of restriction of intramolecular rotation as a cause for aggregation-induced emission

Nitrogen-containing heterocyclic pyrazine luminogens with “free” (1) and “locked” (2) phenyl rings were readily prepared in high yields. The propeller-shaped luminogen 1 shows aggregation-induced emission feature, whereas the disk-shaped chromophore 2 shows conventional aggregation-caused quenching effect, offering a direct evidence to support our hypothesis that restriction of intramolecular rotation is the main cause for the AIE phenomenon.