Cyclopenta[ c ]thiophene- and Diketopyrrolopyrrole-Based Red-Green-Blue Electrochromic Polymers

Cyclopenta[c]thiophene (CPT)-based polymers are potential candidates in organic electronics. Here, we report the first solution-processable red homopolymer (P1) of a thiophene-capped derivative of CPT (DHTCPT), and a blue homopolymer (P2) of N-substituted thienodiketopyrrolopyrrole (DEHTDPP). Additionally, by alternatingly copolymerizing the DHTCPT and DEHTDPP units, we achieved the green copolymer P3, thus completing the red-green-blue color wheels. We have shown experimentally and computationally (time-dependent density functional theory and natural bond orbital calculations) that P1 and P2 have very different optoelectronic features. However, in a donor–acceptor (D–A) copolymer P3, the optoelectronic properties have been tuned significantly to keep it in an intermediate range of P1 and P2. P2 and P3 absorb throughout the whole UV-vis range of the solar spectrum. Furthermore, all polymers showed electrochromism to switch colors between neutral and polaronic states in solution. For P1, the maximum optical contrast (%ΔT) was observed for the SOMO→LUMO transition, whereas P3 displayed the maximum %ΔT at the HOMO→LUMO transition.