Synergistic dielectric and semiconducting properties in fluorescein monopotassium salt random copolymers

Publication date: 7 April 2017
Source:Polymer, Volume 114
Author(s): Zhongqiang Zhao, Zhongbo Zhang, Sandra Pejić, Guoqiang Zhang, Yufeng Zhu, Hewen Liu, Morton Litt, Genevieve Sauve, Lei Zhu
The low dielectric constant (εr ∼ 3–4) for semiconducting polymers has been a major cause for their poor performance compared with the inorganic semiconductors, which possess high dielectric constants above 10. This study aimed to increase the electronic/atomic dielectric constant at high frequencies (i.e., εr∞) for semiconducting polymers. A new design strategy was proposed based on the electric field-induced tautomeric structures in conjugated fluorescein. To achieve this goal, fluorescein monopotassium salt-containing random copolymers were synthesized with 50 and 75 mol.% functionality. To reduce the strong electrostatic attraction between the K⁺ cation and the phenolate anion, 18-crown-6 ether was complexed with K⁺ in the fluorescein copolymers. A relatively high εr∞ of ∼5.5 and high electron mobility of 0.153 cm²/(V·s) were achieved for the 75 mol.% fluorescein K⁺/18C6 copolymer. The high electron mobility could be attributed to the relatively high static dielectric constant (εrs ∼ 9 at 1 Hz) of the sample. The fluorescein monopotassium salt copolymers behaved as n-type semiconductors with an optical band gap around 2.26 eV.

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