Rational design of bio-inspired high-performance ambipolar organic semiconductor materials based on indigo and its derivatives

Indigoids have received much attention as the candidates of sustainable ambipolar organic semiconductor. However, the low charge carrier mobilities extremely limit their practical applications. Therefore, in-depth understanding of their electronic-structure properties and rational molecular modifications are urgently required. Here, we propose a promising strategy to design ambipolar organic semiconductors based on indigo fragments. Moreover, we predicted the organic crystal structures by evolutionary algorithm combined with DFT-D method. Charge transport properties have been significantly improved for the designed molecules, such as narrower energy gaps, higher electron affinity, larger transfer integrals as well as much smaller reorganization energies for hole and electron. Thusly, remarkable ambipolar charge transport behavior has been predicted, for example, the charge carrier mobilities are up to μ_h/μ_e = 7.71/5.42 cm² V^-1 s^-1 for NN-indigo-6,6′-2CN and μ_h/μ_e = 5.15/2.13 cm² V^-1 s^-1 for C₉-NN-indigo-6,6′-2CN respectively.