Donor-acceptor type conjugated porous polymers based on triphenylamine and benzothiadiazole units as ambipolar electrochromic materials

Abstract

Two donor-acceptor (D-A) type conjugated porous polymers (CPPs) named P(TPA-TBTh) and P(TPA-F-TBTh) were prepared on the ITO glass electrodes through Stille coupling reaction under solvothermal condition using triphenylamine (TPA) as the donor and non-fluorinated or di-fluorinated 4,7-bis(thiophen-2-yl)benzo[c] [1,2,5]thiadiazole (TBTh) as the acceptor. The results show that both amorphous CPPs exhibit ambipolar properties in the electrochromic switching and they present completely different morphologies. In the p-type doping process, P(TPA-TBTh) and P(TPA-F-TBTh) fade respectively from neutral purple and neutral reddish purple to oxidized gray. After the n-type doping, P(TPA-TBTh) and P(TPA-F-TBTh) show grass green and emerald green reduced forms respectively. The introduction of fluorine atoms onto the polymer skeleton reduces the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, and makes P(TPA-F-TBTh) have a slightly lower band gap than P(TPA-TBTh). Besides, the non-fluorinated P(TPA-TBTh) and the di-fluorinated P(TPA-F-TBTh) exhibit different electrochromic kinetic properties. The two D-A type CPPs not only provide new structural designs for multicolor electrochromic materials with ambipolar properties, but also achieve the rare green reduction states, thereby deserving attention and further exploration.