1. J. Griffiths, Color and Constitution of Organic Molecules, Academic Press, London (1976).
2. Color Index, 3rd Edition, Vol. 4, The Society of Dyers and Colorists (1971).
3. T. Zincke and H. Binderwald, Chem. Ber. 17, 3026 (1884).
4. P. Gregory, Dyes and Pigments 7, 45 (1986).
5. P. F. Gordon and P. Gregory, Organic Chemistry in Color, pp. 104–108, Springer-Verlag, Berlin, Heidelberg, New York (1983).