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.