Synthesis, characterization, photo physical properties of two isomeric forms of an azo dye supported by DFT calculations and their interaction with DNA

Abstract

A new azo compound 2‐(2‐hydroxyphenylazo)‐indole‐3/‐acetic acid was synthesized. It is a yellow solid when freshly prepared but upon exposure to light turns red gradually. The change in color may be controlled by lowering the temperature or by keeping the compound in the dark. IR and mass spectroscopy of the two forms are similar while UV‐vis, NMR and HPLC are different suggesting isomerization. Fluorescence emission of the yellow compound at 370 nm following excitation at 280 nm is different from the red showing emission at 460 nm upon excitation at 350 nm. Spectroscopy and fluorescence lifetime data suggest change from the yellow form to red is reversible. DFT calculations show the yellow and red forms to be the torsional rotamer and the trans isomer respectively.The cis isomer was determined theoreticallybut could not be isolated.The trans is stable than the cis by 18.825 kcal mol−1.Interaction of the isomers with DNA was studied with the help of UV‐vis and fluorescence spectroscopy. Binding parameters suggest change in spatial orientation makes the trans compound a slightly better binder of DNA than the torsional rotamer.