Comparison of theoretical approaches for predicting the UV/Vis spectra of anthraquinones

Abstract

We have computed the absorption spectra of a large series of anthraquinone dyes using four semi-empirical and ab initio approaches. Without fitting, the ZINDO//AM1 and CIS//HF schemes provide only poor estimates of the λ_max of substituted anthraquinones, with mean absolute errors (MAE) of 80 and 180 nm, respectively, for a set of 45 dyes. These approaches are therefore unable to deliver correct estimates of the colour of anthraquinones. On the contrary, TD-DFT schemes appear to be much more robust and provide MAE under the 20 nm limit. If one uses experimental input to calibrate the theoretical values, subsequently allowing a statistical treatment, the theory–experiment discrepancies become comparable (MAE between 11 and 13 nm) for all four approaches.

Keywords:

• Theoretical approaches
• UV/Vis spectra
• Anthraquinones

Acknowledgements

EP and DJ thank the Belgian National Fund for Scientific Research for their research associate positions. JP acknowledges the FRIA (Belgian ‘Fonds pour la formation à la Recherche dans l’Industrie et dans l'Agriculture') for his PhD grant. Three of the authors (DJ, JP and EAP) are indebted to Professor J-M. André for his long-lasting continuous support. Most calculations were performed at the Interuniversity Scientific Computing Facility (ISCF) installed at the Facultés Universitaires Notre-Dame de la Paix (Namur, Belgium), for which the authors gratefully acknowledge the financial support of the FNRS-FRFC and the ‘Loterie Nationale’ (convention number 2.4578.02) and the FUNDP.