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)[(η 6 -C 6 H 5 )B − (C 6 H 5 ) 3 ] (Rh(nbd)BPh 4 ) 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 (ClO 4 − ), nitrate (NO 3 − ), 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 (CH 3 COO − 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 λ max value for CH 3 COO − 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.