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. © 2014 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.