From P-type to N-type: Peripheral fluorination of axially substituted silicon phthalocyanines enables fine tuning of charge transport

Silicon phthalocyanines (R-2-SiPcs) are a family of promising tunable materials for organic electronic applications. We report the chemistry of the synthesis of axially substituted fluorinated SiPcs (tb-Ph)(2)-FxSiPc (where X = 0, 4, 8, or 16) and explore how the degree of fluorination effects optical and electronic properties. A new treatment with boron trichloride was included to obtain Cl-2-F(X)SiPcs from F-2-F(X)SiPcs, activating the axial position for further functionalization. We observed that as the degree of fluorination increased, so did the electron affinity of the compounds, leading to a drop in frontier orbital levels, as measured by electrochemistry and ultraviolet photoelectron spectroscopy (UPS). The deeper energy levels enabled successful (tb-Ph)(2)-F4SiPc and poly [[6,7-difluoro[(2-hexyldecyl)oxy]-[5,8-quinoxalinediyl]-2,5-thiophenediyl]] (PTQ10) blends for organic photovoltaics and photodetectors. All four compounds were incorporated in organic thin-film transistors (OTFTs), where the degree of fluorination influenced device operation, changing it from p-type conduction for (tb-Ph)(2)-F0SiPc, to ambipolar for (tb-Ph)(2)-F4SiPc, and n-type for (tb-Ph)(2)-F8SiPc and (tb-Ph)(2)-F16SiPc. The OTFT devices made with (tb-Ph)(2)-F16SiPc achieved a low average threshold voltage of 7.0 V in N-2 and retained its n-type mobility when exposed to air.

Automated summary

Silicon phthalocyanines (R-2-SiPcs) are tunable materials for organic electronic applications with promising properties. In this study, we synthesized fluorinated SiPcs and investigated the effect of fluorination on optical and electronic properties. The degree of fluorination impacted the electron affinity and frontier orbital levels of the compounds. The fluorinated SiPcs were successfully used in organic photovoltaics, photodetectors, and organic thin-film transistors (OTFTs) with different conduction behaviors.