N,N,N′,N′- Tetraphenyl-1,4-phenylenediamine−Fluorene Alternating Conjugated Polymer: Synthesis, Characterization, and Electrochromic Application

A novel N,N,N′,N′ -tetraphenyl-1,4-phenylenediamine (TPPA)-containing aromatic dibromide ( 3 ), N, N -bis(4-bromophenyl)- N′, N′ -bis(4-(2,4,4-trimethylpentan-2-yl)phenyl)-1,4-phenylenediamine, was successfully synthesized. The novel conjugated polymer ( 4 ) having number-average molecular weight of 2.05 × 10 4 was prepared via Suzuki coupling from the dibromide ( 3 ) with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester. The conjugated polymer ( 4 ) exhibited excellent solubility in common organic solvents such as N -methyl-2-pyrrolidinone (NMP), tetrahydrofuran, chloroform, and toluene at room temperature. The conjugated polymer ( 4 ) had useful levels of thermal stability associated with their relatively high glass transition temperature ( T g = 144 °C), 10% weight-loss temperatures ( T d10 ) in nitrogen ( T d10 = 445 °C), and char yields at 800 °C in nitrogen (59.0%). The hole-transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the conjugated polymer films cast onto indium−tin oxide (ITO)-coated glass substrates exhibited two reversible oxidation redox couples at E 1/2 value of 0.67 and 1.05 V vs Ag/Ag + in acetonitrile solution. The conjugated polymer film ( 4 ) revealed better stability of electrochromic characteristics and more rapid switching time than model polymers M2 which has no electron-donating bis(4-(2,4,4-trimethylpentan-2-yl) phenyl)amine group and M3 without electron-donating 2,4,4-trimethylpentan-2-yl substituent. The conjugated polymer film ( 4 ) also showed high contrast with color change from pale yellowish to green and then to blue at applied potentials ranging from 0.00 to 1.18 V.