Effective Light‐Induced Fluorescent H‐Aggregation of Fluorinated Pyridyl‐Azo Dye via Photoisomerization.

Here we present the synthesis of a new fluorinated pyridyl‐azo dye and demonstrate an effective way to convert monomer fluorinated pyridyl‐azo dye to H‐aggregated form through UV‐light induced trans‐cis‐trans photoisomerization. And upto a 12 : 88 ratio between monomer : aggregation was achieved through a small pulse of UV irradiation. The H‐aggregation shows a unique high extinction co‐efficient in UV‐visible absorbance and unexpected fluorescence emission with a remarkably large Stokes shift. The solvent DMF and fluorine substituent were found to have a critical role in aggregation. 1H, 19F NMR, and 19F‐DOSY NMR experiments were used to confirm the aggregation and also confirm the absence of π‐π stacking. [ABSTRACT FROM AUTHOR]