2-Methoxynaphthylnaphthoquinone and its solvate: Synthesis and structure-properties relationship

Abstract

Because of their unique visual optic and electronic properties, substituted quinones are commonly used as dyes and pigments; nevertheless, a theoretic background of relationship between the structures and optical properties of such compounds seems to be still undeveloped. Two crystalline forms of 2-methoxynaphth-1-yl-naphthoquinone (MNQ) have been synthesized and characterized by means X-ray, NMR, UV-VIS, as well as, MS spectroscopy. The interpretation of intriguing optical properties of two crystalline forms of MNQ, based on detailed spectral and structural characterization, as well as, DFT and MP2 computations clearly connects the conformation of the molecules with their optical and electronic properties. Thus, flatter conformation, stabilized by crystal net force, favours the intense electron density transition from auxochrome to chromophore moiety (which corresponds excitation from HOMO to LUMO), as well as, favours the π-stacking interaction, that eventually results in colour enhancement. At the same time, small molecules of solvents included into the crystal net allow molecules of arylnaphthoquinones to adopt less rigid conformation what has a dramatic optical outcome. Copyright © 2013 John Wiley & Sons, Ltd.