Tuning the color and electrochromic performance of donor-acceptor polymers through fused-ring acceptor engineering.

Abstract

Conjugated polymers are promising electrochromic materials owing to their tunable optical and redox properties. Herein, two donor-acceptor monomers, BTBTQ and BTTPP, were designed and synthesized using 3-butylthiophene as the donor and dibenzo[f,h]thieno[3,4-b]quinoxaline (BTQ) or thieno[3',4':5,6]pyrazino[2,3-f][1,10]phenanthroline (TPP) as the fused-ring acceptor. Their polymers, PBTBTQ and PBTTPP, were prepared by electrochemical polymerization. Replacing the dibenzo-fused BTQ acceptor with the dipyrido-fused TPP acceptor narrows the optical band gap, whereas the onset oxidation potential of the resulting polymer is shifted from -0.04 V (PBTBTQ) to 0.31 V (PBTTPP). Both polymers switch between a neutral and a fully oxidized state with a well-defined color change. Notably, PBTBTQ achieves an optical contrast of 73.11%, a coloration efficiency of 233.25 cm2 C-1, and coloration and bleaching times of 0.37 and 0.27 s at 1900 nm. These results demonstrate that regulating the electron-deficient character of fused-ring acceptors is an effective strategy for tuning the electrochromic performance of D-A conjugated polymers.

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