DEVELOPMENT OF POLY(ARYLENEETHYNYLENE)S SYNTHESIS AND APPLICATION AS FLUORESCENT SENSOR

Abstract

In this research, we focus on preparation and sensor application of poly(aryleneethynylene)s. Our work is divided into two parts. The first study relates to the utilization of salicylaldimine-functionalized poly(m-phenyleneethynylene) as a turn-on chemosensor for ferric ion (Fe3+). The second part is the preparation of highly pure poly(aryleneethtnylene)s using Pd/CaCO3 as a heterogeneous catalyst. In the first part, a new turn-on fluorescent probe for ferric ion based on poly(m-phenyleneethynylene salicylaldimine) (PPE-IM) is developed. The preparation of PPE-IM involves post-polymerization functionalization of corresponding polymeric amine, PPE-AM, via condensation with salicylaldehyde. Degree of polymerization of both PPE-AM and PPE-IM are 17 with polydispersity index of 1.5. In aqueous solution, polymeric PPE-IM is hydrolytically stable unlike its small molecule analogue which is gradually hydrolyzed. The weak fluorescence of initial PPE-IM at wavelength 470 nm is greatly enhanced by 300 folds upon the addition of Fe3+. 1H-NMR analysis 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 micromolar of Fe3+. In the second part, a commercially available heterogeneous palladium catalyst supported on calcium carbonate (Pd/CaCO3) is studied for preparation of poly(aryleneethynylene)s (PAE)s via Sonogashira coupling polymerization for the first time. The study shows that the use of 10 mol% of Pd/CaCO3 together with commercially available and inexpensive reagents can catalyze C-C coupling polymerization between aryldiethyne and a variety of aryl diiodides/dibromides at 80 oC to provide corresponding PAEs in excellent yields (79-100%) and high degree of polymerization (DP) ranging from 15 to 143 along with polydispersity index (PDI) range of 1.5 to 3.8. The catalytic activity of this Pd/CaCO3 is comparable to the classical heterogeneous, Pd/C catalyst and homogeneous Pd(PPh3)4 catalyst. While Pd/CaCO3 catalysed reaction gives much lower Pd and Cu contaminations in the resulting polymers. In summary, a highly sensitive and selective fluorescence turn-on sensor for Fe3+ is developed from poly(aryleneethnylene)s via post polymerization functionalization (part A). The heterogeneous polymerization using Pd/CaCO3 catalyst is developed for preparation of highly pure poly(aryleneethnylene)s (part B).