π‐Conjugated polyfluorenes with o‐phenylenediamine unit: Synthesis, optical and electrochemical properties, charge transfer complexation, and DNA sensing

Abstract

Abstractπ‐Conjugated polyfluorenes (PPs) comprising 2,3‐diaminobenzene‐1,4‐diyl (unit A) and 9,9‐dihexylfluorene‐2,7‐diyl (polymer‐1) or 9,9‐bis(6‐N,N,N,‐trimethylammoniumhexyl)fluorene‐2,7‐diyl (unit B) (polymer‐2) units were synthesized using Suzuki‐Miyaura coupling polycondensation. To compare the chemical properties and functionality of polymer‐2, a water‐soluble PP comprising benzene‐1,4‐diyl and unit B (polymer‐3) was synthesized. Polymer‐1 exhibited solvatochromism: the photoluminescence (PL) peak of the polymer in solutions shifted to a longer wavelength with an increase in the dielectric constants of solvents. Polymer‐1 formed charge transfer (CT) complexes with organic electron acceptors. The CT complexation behavior was systematically elucidated by the PL measurements using Stern–Volmer and Benesi–Hildebrand methods. Water‐soluble polymer‐2 could be used as a sensor for the chain length of telomere DNA by monitoring the changes in its PL intensity upon the addition of the analyte. The DNA sensing performance of polymer‐2 surpassed that of polymer‐3, attributed to the presence of unit A in polymer‐2. This unit brought polymer‐2 closer to DNA through hydrogen bonding between the amino group of polymer‐2 and nucleic acids in DNA. This interaction facilitated the occurrence of CT from the polymer backbone to DNA.