Conjugated copolymers bearing 2,7-dithienylphenanthrene-9,10-dialkoxy units: highly soluble and stable deep-blue emissive materials

Abstract

Conjugated copolymers PNP1–4 were prepared from the palladium catalyzed Suzuki–Miyaura cross-coupling reaction of 2,7-dithienylphenanthrene units – bearing various alkoxy groups – PNM1–4 and 9,9-dioctylfluorene-2,7-diboronic acid FBA. The formation of copolymers PNP1–4 was confirmed by different analytical techniques, such as, gel permeation chromatography (GPC), thermogravimetry analysis (TGA), ¹H- and ¹³C-nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), UV-vis absorption and emission spectroscopies. The target copolymers were found to have a relatively high thermal and chemical stability as well as an excellent solubility in common organic solvents. GPC traces of copolymers PNP1–4 display noticeably large weight-average (M_w) molecular weights in the range of 36.5–152.0 kDa and a polydispersity index (Đ = M_w/M_n) of 2.5–3.0. Photophysical analysis of PNP1–4 divulges their luminescence in the deep blue region, namely, in the range of 453–463 nm with an emission quantum yield up to 17%. In addition, copolymers PNP1–4 were explored as field-effect transistors revealing a hole mobility up to ∼6.4 × 10⁻⁶ cm² V⁻¹ s⁻¹.