Optical and Chiroptical Output of Anion Recognition Event Using Clustered Sulfonamide Groups Organized on Poly(phenylacetylene) Backbone

Three-dimensionally organized sulfonamide groups have been demonstrated to show an anion signaling ability using poly(phenylacetylene) with L-aspartic acid and sulfonamide functionalities (poly-1). The polymerization of N-4-ethynylphenylsulfonyl)-L-aspartic acid diethyl ester (1) was carried out using Rh+(2,5-norbornadiene)[(eta(6)-C6H5)B-(C6H5)(3)] (Rh(nbd)BPh4) as a catalyst to afford poly-1. The biased helical conformation of poly-1 was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of the anions including perchlorate (ClO4-), nitrate (NO3-), azide (N-3(-)), and bromide (Br-) anions had fundamentally no effect on both the CD and UV profiles of poly-1. On the other hand, the addition of the anions including acetate and fluoride anions (CH3COO- and F-) into the poly-1 solution intensified the CD responses of the poly-1, showing that the anion recognition of sulfonamide groups induced distinct changes in the poly(phenylacetylene) backbone. In addition, a distinct red shift was observed for poly-1 in the presence of these two anions; i.e., the lambda(max) value for CH3COO- changed from 408 to 447 nm, and that for F- changed from 408 to 482 nm. The guest specificity observed in the solution color change of poly-1 with counteranions clearly correlated with the guest basicity.