Conjugated helical polymers: End-group control and coupling reactions

Abstract

Telechelic helical poly(phenyleneethynylene)s 2 and 3 bearing end iodo and ethynyl groups were synthesized by the Sonogashira–Hagihara coupling reaction of prepolymer 1 with N-α-tert-butoxycarbonyl-3,5-diiodo-4-hydroxy-d-phenylglycine hexylamide (4) and p-diethynylbenzene (5), respectively. Polymer 2 was treated by Sonogashira–Hagihara coupling reaction with 1,6-diethynylpyrene (a) and 4,4-diethynylbiphenyl (b) to obtain the corresponding polymers 2a and 2b. Polymer 2 was also subjected to the Mizoroki–Heck coupling reaction with diphenyl(p-vinylphenyl)phosphine (e) to obtain the corresponding polymer 2e, and the incorporation of the phosphine moieties was confirmed by 31P NMR spectroscopy. In a similar fashion, polymer 3 was polymerized with 1,4-dibromonaphthalene (c) and 9,10-dibromoanthracene (d), but no concrete evidence for the formation of polymers 3c and 3d was observed. Circular dichroism (CD) spectroscopic analysis revealed that all the polymers adopted folded helical conformations with predominantly one-handed screw sense in CHCl3. The polymers exhibited photoluminescence (PL) depending on the incorporated functional groups.