Mild synthesis and photophysical properties of symmetrically substituted diketopyrrolopyrrole derivatives

A series of symmetrically substituted diketopyrrolopyrrole derivatives were synthesized under mild conditions in good yields. All of the diketopyrrolopyrroles were characterized by 1H and 13C NMR, ultraviolet-visible and fluorescence spectroscopy, high resolution mass spectrometry and elemental analysis. The maximum absorption and emission bands showed gradual red-shift with the increase in electron donating strength of the 3,6-substituent. In addition, the optical properties of 4,4'-(2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-3,6-dioxo- 2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)dibenzoic acid and 3,6-bis(4-hydroxyphenyl)-2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethy l )pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione were investigated under alkaline conditions. The results demonstrated that 3,6-bis(4-hydroxyphenyl)-2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethy l )pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione could be employed as an acid-base indicator. These diketopyrrolopyrroles derivatives have potential application in the synthesis of novel organic optoelectronic materials and in biological systems as a consequence of the increased water solubility.