Post-Polymerization Functionalization Approach for Highly Water-Soluble Well-Defined Regioregular Head-to-Tail Glycopolythiophenes

Two bromide-bearing regioregular head-to-tail polythiophenes (polymers 1 and 3 ) were prepared by using Grignard metathesis method to polymerize 2,5-dibromo-3-bromohexylthiophene (2) and 2,5-dibromo-3-(11-bromo-3,6,9-trioxa-1-undecoxy)thiophene ( 7 ), respectively. Well-defined regioregular head-to-tail glycopolythiophenes were prepared through post-polymerization functionalization approach by treating the bromide-bearing polythiophenes with 1-thiolethyl-α- d -mannose tetraacetate ( 3a ) or 1-thiol-β- d -glucose tetraacetrate ( 3b ) in THF solution with a basic condition, respectively, and followed by sequential deacetylation under Zemplén conditions in methanol and methylene chloride containing sodium methoxide at room temperature. Glycopolythiophenes (polymers C and D ) with hydrophilic tetra(ethylene glycol) as tethered spacers between the polymer backbone and carbohydrate residues are highly water-soluble while glycopolythiophenes (polymers A and B ) with hydrophobic hexyl tethered spacers are completely insoluble in water. All polythiophenes display low fluorescence with fluorescent quantum yield ranging from 0.4% to 3%. However, water-soluble polymers C and D in 0.1 M phosphate buffer (pH 7.2) show a little higher fluorescent intensity than their precursor polymer 3 in chloroform solution. α-Mannose-bearing glycopolythiophene (polymer C ) exhibits specific binding to Concanavalin A through multivalent interactions with a binding constant of 2.15 × 10 5 .