CONDUCTING POLY(3,4-ALKYLENEDIOXYTHIOPHENE) DERIVATIVES AS FAST ELECTROCHROMICS WITH HIGH-CONTRAST RATIOS

A series of alkyl-substituted and unsubstituted poly(3,4-alkylenedioxy thiophene)s were synthesized electrochemically using 3,4-alkylenedioxy thiophene derivative monomers where either the size of the alkylenedio xy ring or the nature of the pendent group was varied. The specific sy stems studied include 3,4-ethylenedioxythiophene (EDOT), 2-methyl-2,3- dihydrothieno[3,4-b][1,4]dioxine (EDOT-Me), 2-tetradecyl-2,3-dihydroth ieno[3,4-b][1,4]dioxine (EDOT-C14H29), 2-phenyl-2,3-dihydrothieno[3,4- b][1,4]dioxine (EDOT-Ph), 3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine ( ProDOT), -methyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT-Me ), 2,3,4,5-tetrahydrothieno[3,4-b][1,4]dioxocine (BuDOT), and 5,10-dih ydrobenzo[f]thieno[3,4-b][1,4]dioxocine (BuDOT-Xyl). Optoelectrochemic al experiments revealed that the nature of the substitution on the pol ymers had little effect on the extent of conjugation of the backbone a s evidenced by electronic band gaps for all polymers of approximately 1.7 eV (730 nm). These electrochromic polymers switch from a relativel y transmissive light: green in the oxidized form to an opaque dark blu e in the reduced form, with the highest electrochromic contrast ratios accessible for PBuDOT and PEDOT-C14H29. Multiple switching studies mo nitoring the electrochromic contrast showed that ca. 300 nm thick poly mer films could be fully switched between their reduced and oxidized f orms in 0.8-2.2 s with Delta%T of 44-63%. In situ conductivity studies carried out on relatively thick polymer films (2.7-9.5 mu m) deposite d between large gap (200 mu m) lateral growth electrodes demonstrated the low-potential turn-on for these materials, and maximum conductivit ies of 0.2-12.1 S/cm were attained.