Molecular Design, Syntheses, and Physical Properties of Nonpolymeric Amorphous Dyes for Electron Transport

Relationships between electrical properties and molecular structures for various nonpolymeric amorphous dyes were investigated. Absorption maximum wavelengths (λobs) for amorphous films were found to be nearly equal to those for solution samples. When the parameters of the used PPP−CI MO method were modified so as to reproduce the λobs values, the calculated HOMO and LUMO energy levels corresponded with the reported ionization potential (I p) and electron affinity (E A) values. Electric carrier transport properties between dye films and metal electrodes (Au or Al) were found to be correlated with the HOMO and LUMO levels. For strong donor and acceptor dyes, impurity carrier effects were generally observed. For weak donor and acceptor dyes, carrier injection was difficult. Carrier injection phenomena without the influence of impurities were observed for moderate donor and acceptor dye films. Amorphous dyes with cyanovinyl substituents or oxadiazole rings were designed to allow reversible electron transport and were newly synthesized.