Conjugated polyelectrolytes, in which the charged groups are incorporated into the side chain end, have attracted much attention. These charges make them water-soluble and allow molecular recognition, which is together with their strong fluorescence and sensitivity to the changes in structure and charge distribution. Among various conjugated polymers, polyfluorenes show strong luminescence, and their solubility and optical properties can be controlled by introducing the ionic group at the 9-position. In this study, in order to investigate the effect of the biomolecular recognition on the adsorption capacity of polyfluorenes with phosphonium groups, trimethylphosphonium substituted polyfluorene (PTMPHF) were synthesized, and their optical properties were investigated. A precursor polymer of PTMPHF, poly(9,9-bis(6-bromohexyl)fluorene) (PBHF), was synthesized by Kumada catalyst transfer polycondensation. PBHF with the Mn values in the range of 6.3-13.0 kgmol-1 and PDI values of ~1.20 were obtained. The Mn of PBHF increased linearly against [Monomer]/[Ni(acac)2], assuming that the polymerization follows the living mechanism. PTMPHF was obtained by reacting PBHF with trimethylphosphine. The phosphonium conversion ratios of the polymers determined by 1H NMR were 100%. The obtained PTMPHFs were soluble in dimethyl sulfoxide (DMSO), methanol, and partially soluble in water. UV-vis absorption and fluorescence measurements of PTMPHF (m = 26) in Tris-HCl buffer solution containing 1 vol% DMSO at pH = 8.0 were conducted. The maximum absorption peak was observed at 413 nm, and the maximum fluorescence was observed at 429 nm upon excitation at 395 nm. The decrease in fluorescence intensity upon the addition of biomolecules was monitored, particularly by the addition of RNA and single stranded DNA (ssDNA). Moreover, there is a bathochromic wavelength shift, which suggests the formation of a complex between PTMPHF and RNA or ssDNA that has an intrinsic fluorescence. Among the ssDNA, PTMPHF showed higher sensitivity to cytosine based ssDNA.

Polyelectrolyte complexes of a cationic polyfluorene with biomolecules

254th National Meeting (2017)

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