Theoretical study on the transport properties of oligothiophene–diketopyrrolopyrrole derivatives: quinoidal versus aromatic

Abstract

Density functional theory calculations were carried out to investigate the transport mechanism of three oligothiophene–diketopyrrolopyrrole (T-DPP) derivatives. The results show that quinoidal molecule 1 that has dicyanovinyl has lower the lowest unoccupied molecular orbital (LUMO) energy level and larger adiabatic electron affinity (EAa) comparing with quinoidal 2 that has monocyanovinyl as terminal groups, signifying that to increase the extent of quinoid could improve the stability of the molecules in the air. Moreover, quinoidal molecules 1 and 2 have lower LUMO energy level, larger EAa, and electron-transfer integral (Ve) comparing than aromatic molecule 3, which indicates that quinoidal T-DPP derivatives are more in favor of electron than hole transport compared with their aromatic ones. Thus, constructing quinoidal architecture was also an effective way to design n-type transport materials besides the conventional idea that introducing electron-withdrawing groups.