High performance ambipolar semiconductor of pyridine-capped diketopyrrolopyrrole-porphyrin oligomers: Roles of thiophen substitution and oligomer length

Abstract

Series of seven donor-acceptor pyridine-capped diketopyrrolopyrrole − 5,15-diacetylenyl-10,20-diaryl-porphyrinato zinc oligomers nPyDPP-PAr [n = 1–3, Ar = methyl-benzothiophene (BT) or methyl thiophene (T) or methylbenzene (B)] were designed. Density functional theory calculations were performed to theoretically study the molecular geometry, electronic structure, and charge transport properties of the seven donor-acceptor compounds. The effects of oligomer length and different Ar groups on the crystal packing mode and charge transport properties were systematically studied. Thiophen substitution reduces the electron injection barrier, diminishes the reorganization energy, enlarges the charge transfer integral, and therefore shows three-to-one role for ambipolar semiconductor with large charge transfer mobility. Extending the π-conjugated backbone not only improves the semiconductor performance, but also makes the ambipolar performance more balanced. 3PyDPP-PT and 3PyDPP-PBT show high hole/electron transfer mobility as high as 8.28/7.90 cm2 V−1 s−1 and 9.00/9.79 cm2 V−1 s−1, respectively.