An effective and efficient way was developed to convert monomer fluorinated pyridyl-azo dye to H-aggregated through UV-light induced trans-cis-trans photoisomerization.

Abstract

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.