Strikingly different electronic spectra of structurally similar perylene imide compounds

Perylene imide derivatives are well known organic pigments and have also attracted attention as photoconductors for electrophotographic photoreceptors as well as materials for optical disks. N,N′-di-bis(2-(4-phenyl)ethyl)perylene-3,4:9,10-bis(dicarboximide) (i.e. 4-phenylethyl derivative: EPH) is a commercial black pigment. However, 4-pyridylethyl derivative (EPY) is found to exhibit a vivid red as well as black color, depending on the solvent used for recrystallization. Furthermore, the color changes from black to vivid red around 100 °C. In order to study the correlation between color and constitution, structure analysis was carried out on both materials of EPY. Then, we found two kinds of molecular conformation in EPY: cis and trans forms. The red color arises from a solid with the cis form while the black one is characteristic of the trans form. The mechanism of the two different colors has then been interpreted as arising from a different fashion of molecular arrangement and its characteristic excitonic interactions. In addition, the transformation from the black phase to the red one is found to be applicable to DVD-recordable disks that operate with a laser diode of 635 nm.