The Effects of Methoxylated Isoindigo on the Optical and Charge Transport Properties of the Corresponding Polymers

Although the effects of electron-deficient group substitution on isoindigo on the corresponding conjugated polymers are extensively studied, the modification of isoindigo core with electron-rich groups has not been investigated. It is envisioned that the introduction of the methoxy group on isoindigo will not only tune the highest occupied molecular orbital (HOMO) energy level of the corresponding polymers but also introduce O center dot center dot center dot S "conformation lock" to increase the coplanarity of the polymers, which should facilitate hole transport. Herein, the syntheses of two methoxylated isoindigos and the investigations on the charge transport behaviors of their copolymers with bisthiophene (2T) and bisthiazole (2Tz) are reported. It is found that the substitution positions have a drastic influence on the UV-vis absorption and electrochemical properties for both monomers and polymers. Theoretical calculations and single crystal structure analysis confirm the existence of O center dot center dot center dot S "conformation lock", however, both methoxy substitutions also change the aggregation behaviors of the corresponding polymers to a mixed face-on/edge-on orientation which has an adverse effect for charge transport. Among the four polymers, the polymer of 5,5'-methoxylated isoindigo and 2T exhibit the best hole mobility of 1.9 x 10(-1) cm(2) V-1 s(-1).