1. 3) K. Venkataraman : “The Chemistry of Synthetic Dyes”, II, p.705, Academic Press, New York, 1952
2. 4) a) J. Griffiths : “Colour and Constitution of Organic Molecules”, Academic Press, London, 1976 b) J. Griffiths, K. J. Pender : Dyes and Pigments, 2, 37 (1981) c) J. Fabian, H. Hartmann : “Light Absorption of Organic Colorants”, SpringerVerlag, Berlin, 1980