Knoevenagel condensation of 2-formyl-octamethylcalixpyrrole with selected 1,3-indanedione derivatives yields calixpyrrole anion sensors with push-pull chromophores displaying strong intramolecular charge transfer. The push-pull feature results in augmented signal output as well as in dramatic changes in anion selectivity exemplified by a 50-fold increase in acetate vs chloride selectivity compared to the parent calixpyrrole.
Nishiyabu, Ryuhei and Anzenbacher, Pavel Jr., "1,3-indane-based Chromogenic Calixpyrroles With Push-pull Chromophores: Synthesis And Anion Sensing" (2006). Chemistry Faculty Publications. 184.