Electropolymerization nanoarchitectonics of different bithiophene precursors for tuning optoelectronic performances of polythiophenes

Due to the characteristics of good charge mobility and easy modification, bithiophene unit has attracted more and more attentions in the field of organic electronics. Herein, in this work, 2,2 '-bidithiophene (2BTP), 2,3 ' bithiophene polymers (3BTP) and 3,3 '-bithiophene (4BTP) and their polymers was systematically investigated. All of them were electropolymerized into the corresponding electrochromic polymer films (P2BTP, P3BTP, and P4BTP). Although 4BTP can't be synthesized by electrochemical methods due to its excessive steric hindrance, the 2BTP and 3BTP could be facile polymerized smoothly. It was also found that both the P2BTP and P3BTP show remarkable electrochromic properties: high optical contrast (P2BTP: 23%, P3BTP: 26%), favorable coloration efficiency (P2BTP: 125.2 C-1 cm2, P3BTP: 145.9 C-1 cm2), obvious color contrast (P2BTP: from red to dark green, P3BTP: from yellow to dark green), and fast response time (P2BTP: 0.58 s). This study will help us to further understand the effect of different bithiophene unit on the properties of the resultant conductive polymers and provide important guidelines for the development of high-performance electrochromic materials.