New Ambipolar Organic Semiconductors. 1. Synthesis, Single-Crystal Structures, Redox Properties, and Photophysics of Phenoxazine-Based Donor−Acceptor Molecules

We report the synthesis and structural, photophysical, and electrochemical properties of a series of eight new phenoxazine-based donor−acceptor molecules utilizing phenoxazine as a common donor and quinoline, quinoxaline, benzoylquinoxaline, and benzoquinoxaline as various electron acceptor moieties. The phenoxazine−phenylquinoline molecules crystallized in the monoclinic system with the space groups C 2/ c and P 2 1 / c, respectively, revealing a 169° dihedral angle in the phenoxazine unit. The new materials had high glass transition temperatures (128−193 °C) and ambipolar redox properties with reversible electrochemical oxidation and reduction. Their HOMO levels were at 5.1−5.2 eV, whereas their LUMO levels (2.3−3.0 eV) increased with the electron acceptor strength. The materials showed intramolecular charge transfer fluorescence in dilute solutions with emission colors varying from blue to red and a quantum yield ranging from 86% in the phenoxazine−biphenyl molecule to as low as 16% in the benzoquinoxaline-containing molecule. Density functional theory calculations provided insight into the molecular geometry and electronic structures of the donor−acceptor molecules and were in good agreement with the experimental results. These results demonstrate that the new phenoxazine-based donor−acceptor molecules represent a new class of promising ambipolar semiconductors for organic electronics.