A new turn on fluorescent probe for ferric ion based on poly(m-phenyleneethynylene salicylaldimine) (PPE-IM) has been developed. The preparation of PPE-IM involves post-polymerization functionalization of the corresponding polymeric amine, PPE-AM, via the condensation with salicylaldehyde. The degree of polymerization of both PPE-IM and PPE-IM is 17 with polydispersity index of 1.5. In aqueous solution, the polymeric PPE-IM is highly stable unlike its small molecule analog which is gradually hydrolyzed. The weak fluorescence of initial PPE-IM (lambda(em) = 470) is greatly enhanced by 300 folds upon the addition of Fe3+. The H-1 NMR reveals that the fluorescence enhancement is caused by Fe3+-induced hydrolysis of the imine group. The sensing system shows a detection limit of 0.14 mu M of Fe3+. (C) 2018 Wiley Periodicals, Inc.