Triphenylamine-based linear conjugated polyfluorenes with various pendant groups: Synthesis, characterization, and ion responsive properties

This study describes the synthesis of three triphenylamine-based linear conjugated polyfluorenes, differing in the proton (PFH), aldehyde (PFCHO), and 4′-(4-vinylphenyl)-2,2′:6′,2″-terpyridine (PFTPY) pendant groups that attach to the para position relative to 4,4′-dibromotriphenylamine monomer, by using Suzuki coupling polymerization. The structural effect on optical properties and the effect of the terpyridine unit on sensory characteristics of fluorescent chemosensors were investigated. The molecular structures, as well as the thermal, optical, and electrochemical properties of the polymers, were characterized by using 1H NMR, elemental analysis, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analyzer, absorption, photoluminescence spectroscopies, and cyclic voltammetry. These polymers were soluble in common organic solvents and exhibited favorable thermal stability with a thermal decomposition temperature above 393.3 °C. The ionization potentials of the polyfluorene derivatives (PFH, PFCHO and PFTPY) were decreased after introducing the triphenylamine segments, as confirmed by the highest occupied molecular orbital level (5.22–5.42 eV) below vacuum relative to PF without a triphenylamine segment (5.65 eV). PFTPY with a pendant terpyridyl unit showed higher sensitivities to Fe3+ and Ni2+, as compared with other metal ions. Adding a Zn2+ ion not only caused partial fluorescence quenching but also induced a broad emission peak in the range of 525–700 nm. PFTPY revealed higher fluorescence quantum yields (ΦPL = 0.44), suggesting that it is a promising material for PLED and chemosensor candidates.