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

Abstract

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)[(η6-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 (N3−), 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 λmax 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.