Control of Molecular Orientation in Organic Semiconductor Films using Weak Hydrogen Bonds

Use of the intrinsic optoelectronic functions of organic semiconductor films has not yet reached its full potential, mainly because of the primitive methodology used to control the molecular aggregation state in amorphous films during vapor deposition. Here, a universal molecular engineering methodology is presented to control molecular orientation; this methodology strategically uses noncovalent, intermolecular weak hydrogen bonds in a series of oligopyridine derivatives. A key is to use two bipyridin-3-ylphenyl moieties, which form self-complementary intermolecular weak hydrogen bonds, and which do not induce unfavorable crystallization. Another key is to incorporate a planar anisotropic molecular shape by reducing the steric hindrance of the core structure for inducing π-π interactions. These synergetic effects enhance horizontal orientation in amorphous organic semiconductor films and significantly increasing electron mobility. Through this evaluation process, an oligopyridine derivative is selected as an electron-transporter, and successfully develops highly efficient and stable deep-red organic light-emitting devices as a proof-of-concept.