Photophysical and electrochemical properties and temperature dependent geometrical isomerism in alkyl quinacridonediimines

Abstract

Quinacridone diimines 1–10 were synthesized by the condensation of anilines with alkyl substituted quinacridones (QA). Photophysical and electrochemical properties of the compounds were investigated. Unconventional behavior of absorption spectra suggested a decrease in π^_conjugation within the QA skeleton as well as lack of extended π^_conjugation between the QA skeleton and the N-phenyl rings. A computational study of compounds 1–10, a variable temperature ¹H NMR study of compounds 2, 7 and 10 (for instance), and single crystal X-ray analysis of 2, 3, 6, 7, 8 and 10 indicated that the anomalous behavior is due to the buckled, non-planar structure of the quinacridones. Moreover the molecules existed in two interconvertible geometric isomeric forms at different temperatures. Molecular orbital calculations were performed at B3LYP/6-31+G(d), B3PW91/6-31G(d) and PBEPBE/6-31G(d) levels of theory at B3PW91/6-31G(d) optimized structures for both isomers of all compounds (1–10); the results obtained are in close agreement with the experimentally determined values.