HOMO and LUMO energy levels of N,N′-dinitrophenyl-substituted polar diketopyrrolopyrroles (DPPs)
作者:Martin Vala、Jozef Krajčovič、Stanislav Luňák、Imad Ouzzane、Jean-Philippe Bouillon、Martin Weiter
DOI:10.1016/j.dyepig.2014.03.005
日期:2014.7
A series of four [3,4-c]pyrrole-1,4-diones (diketopyrrolopyrroles, DPPs) with (substituted) phenyl rings in 3,6-positions was prepared by direct N,N'-arylation of corresponding diketopyrrolopyrrole pigments with 1-fluoro-2,4-dinitro-benzene. While the energies of the HOMO levels depend strongly on the nature of the p-substituehts on the 3,5-phenyl rings, the LUMO levels obtained by cyclic and rotating disc voltammetry were found to be almost independent of the substituent. The absorption spectra show either a hypsochromic or bathochromic shift with respect to parent pigments, depending on the electron-donating and -accepting character of the p-substituents. This behaviour was rationalized by density functional theory calculations, showing that highest occupied molecular orbital is delocalized over the whole 3,6-diphenyl-diketopyrrolopyrrole conjugated system as in the parent pigments, while low-lying LUMO is completely different from the precursors, as it is localized exclusively on the 2,4-dinitrophenyl substituents, i.e. its shape and energy are not affected by a substitution on the 3,6-phenyl rings. (C) 2014 Elsevier Ltd. All rights reserved.