1. Allmann, R.: Structural chemistry. In: The chemistry of the hydrazo, azo and azoxy groups — Part 1, Patai, S. (ed.), pp. 44–45. London, New York, Sydney, Toronto: John Wiley and Sons 1975
2. Zollinger, H.: Azo and diazo chemistry, pp. 59 and 293. New York, London: Interscience 1961
3. Fabian, J., Hartmann, H.: Light absorption of organic colorants: Theoretical treatment and empirical rules, pp. 42–50. Berlin, Heidelberg, New York: Springer-Verlag 1980
4. Bershtein, I. Ya., Ginzburg, O. F.: Russian Chem. Rev. 41, 97 (1972)
5. Ref. A2.: pp. 322–337