Color Generation Mechanism of Quinacridone Derivatives as Viewed from the Intermolecular Hydrogen Bond

摘要

Quinacridones are industrially important hydrogen-bonded pigments. The shade in the solid state is vivid red while pale yellow in solution, indicating the involvement of intermolecular interactions in the color generation. The electronic structure has therefore been investigated based on the crystal structure with special attention to the intermolecular N-H...O hydrogen bond using four kinds of quinacridone compounds with different H-bond forming characteristics: unsubstituted quinacridone (γ-QA), mono-N-methylquinacridone (MMQA), N,N'-dimethyl-quinacridone (DMQA) and 2,9-dimethylquinacridone (2,9-DMQA). γ-QA, 2,9-DMQA and MMQA are found to form three-dimensional ("hunter's fence"), two-dimensional (sheet-like) and one-dimensional (chain-like) hydrogen bond networks, respectively. The present H-bond aligns the transition dipole in a way "head-to-tail". The bathochromic shift upon crystallization (pale yellow to vivid red) is mostly attributed to resonance interactions between transition dipoles.