Aggregation induced emission in the rotatable molecules: the essential role of molecular interaction

Aggregation-induced emission (AIE) compounds, dye2 and dye3, with a rotatable N–N single bond and aza-crown-ether, have been synthesized. The fluorescence intensities of both dyes are very weak in THF, while become extraordinarily strong in a mixture of H2O–THF (v/v 95%). They are increased by 88.9 and 70.7 times, respectively, indicating enhanced blue-green fluorescence emissions. The λem of these two compounds in different states has been well studied. Besides this, dye1 and dye2 were characterized by single crystal X-ray structural determination. The results show that molecular interactions are formed in the particles, which considerably restrict the intramolecular vibration and rotation.