Preparation pyrene bearing asymmetric block copolymer for sensing applications as a fluorescent chemosensor

Abstract

Herein, a pyrene based fluorescence chemosensor was designed with vicinal diol pendant groups for sensing application of various targeted analyte such as boric acid via aggregation induced emission. In this protocol, first hydrophilic poly(oligo (ethyleneglycol) methacrylate) (POEGMA) macro-CTA was synthesized via RAFT polymerization. Then, poly(oligo (ethyleneglycol) methacrylate)-block-poly(glycidyl methacrylate)-co-poly(4-(1-pyrenyl)-styrene) (POEGMA-b-PGMA-co-PPySt) block copolymer was prepared via chain extension of POEGMA by RAFT polymerization technique. Then, epoxy units of the PGMA segment were opened in two ways to obtain many vicinal diol groups either by reaction with Trizma base or basic aqueous medium. Resulting asymmetric hydroxyl functional block copolymer expected to exhibit chelating units towards to boric acid from the hydroxyl and/or seconder amine units. By this way, the polymer loss the hydrophilicity from this complexation with the targeted analyte which forces to make agglomeration. This agglomeration triggered the formation of excimer emission via π-π interaction of the pyrene units. This novel approach simply provides selective detection of boric acid detection in aqueous medium. Most of the agglomeration induced emission studies carried out by solvent manipulation, in our case, it was thought that the agglomeration induced by the complexation of targeted analyte. The demonstrated route has novelty on different analytes by simply changing the chelating units of asymmetric block copolymers. The critical point of the material is balancing the hydrophilic and hydrophobic ratio of the block copolymer to get the agglomeration after the complexation of the analyte. Overall, a simple sensing method was represented with this pyrene and vicinal diol bearing asymmetric block copolymer. The resulting tailored polymer molecular weights and repeating units were approximately calculated with 1H-NMR and polydispersity index (PDI) was determined from the GPC traces. From the results, repeating units of POEGMA was calculated as 40, MNMR as 12300 g/mol with 1.10 PDI; for POEGMA-b-PGMA-co-PPySt block copolymer these values were 40:16:2 (OEGMA:GMA:PySt), 15200 g/mol with 1.20 PDI. As for two potential chemosensors, tris tethered and NaOH treated block copolymers, MNMR was found as 17100 g/mol with 1.09 PDI and 15500 g/mol with 1.27 PDI respectively. According to GPC and 1H-NMR results, it was understood that the polymerization reactions proceed in a controlled manner successfully. Optical properties of the block copolymers were evaluated by UV-Vis and fluorescence spectrometer. For tris tethered POEGMA-b-PGMA-co-PPySt and POEGMA-b-PGlyMA-co-PPySt block copolymers in THF, maximum absorption and emission values were found as λabs = 347 nm, λems = 403 nm; λabs = 346 nm, λems = 407 nm under optimized conditions, respectively.