The Crystal Spectra of Molecular Compounds of 1,6-Diaminopyrene

Abstract

Abstract Polarized absorption spectra were observed on the single crystals of molecular compounds which involve 1,6-diaminopyrene as electron donor and p-chloranil, p-bromanil, p-iodanil, and tetracyano-p-quinodimethane as electron acceptor. It is shown that, in spite of the low ionization potential of diaminopyrene 6.56 eV, its solid molecular compounds with chloranil, bromanil, and iodanil are of non-ionic type, and their crystal spectra exhibit the general features characteristic of a typical charge-transfer molecular compound composed of neutral molecules. The diaminopyrene-TCNQ, compound was found to be of ionic type. Although the bromanil and iodanil compounds of diaminopyrene exhibit two charge-transfer bands, in the region below 10 kK and at about 20 kK respectively, the chloranil compound does not show the near-infrared charge-transfer band corresponding to the charge transfer from the highest occupied orbital of the donor to the lowest vacant orbital of the acceptor. A discussion is given for this phenomenon from the overlap between the donor and acceptor orbitals.