1. A. I. Kiprianov, Tsvet i stroenie tsianinovykh krasitelei [Color and Structure of Cyanine Dyes], Naukova Dumka, Kiev, 1979, 666 pp. (in Russian).
2. W. S. Matthews, J. E. Bares, J. E. Bartmess, F. G. Bordwell, F. J. Cornforth, G. E. Drucker, Z. Margolin, R. J. McCallum, G. J. McCollum, N. R. Vanier, J. Am. Chem. Soc., 1975, 97, 7006.
3. R. Kuhn, H. Fischer, F. A. Neugebauer, H. Fischer, Liebigs Ann. Chem., 1962, 654, 64.
4. A. W. Johnson, R. B. LaCount, Tetrahedron, 1960, 9, 130.
5. M. J. S. Dewar, R. C. Dougherty, The PMO Theory of Organic Chemistry, Plenum Publ. Corp., New York, 1975, 576 pp.