Design and synthesis of novel V-shaped AIEE active quinoxalines for acidochromic applications

A series of novel V-shaped quinoxaline derivatives (QDs) was designed, synthesized and characterized and their photophysical and thermal properties were investigated. Single crystal X-ray diffraction studies of QD1, QD(3) and QD6 indicated twisted structure and all were found to be AIEE active except one. All QDs, except two, showed visual color change from colorless to yellow-green upon treatment with TFA accompanied by turn-on ratiometric response while pyridopyrazine derivative PP1 showed turn-on response in DCM solution. These changes were reversible upon treatment with TEA. Treatment of QD1 and PP1 with TFA as well as with other acids like HCl and HNO3 also caused similar color changes whereas H2SO4 caused visual color change from colorless to red. Further, Job's plot confirmed the 1:2 and 1:3 binding stoichiometry of QD1 and PP1 with TFA, respectively. NMR studies also confirmed the binding interactions between QDs and TFA and reversibility upon treatment with TEA. Acid sensing behavior and reversibility of QD1 and PP1 was also investigated in solid state. Additionally, good to excellent thermal stability was indicated by thermogravimetric analysis with the thermal decomposition temperatures (T-d) in the range of 225-425 degrees C.