The structure of cyanine dyes of tetrazoloisoindole row. 1. Bis-(1-Methyltetrazolo[5,1-a]isoindole-5)monomethyncyanine perchlorate

X-ray examination, ab initio quantum-chemical calculations and analysis of 13C NMR spectra for the simplest monomethyncyanine of tetrazoloisoindole row have been performed. Appropriateness of concept of consideration of such compounds as carbocationic structures has been discussed. Application of Natural Bonding Orbitals theory reveals that main contribution to the total structure of cation is provided by three resonant forms, in which positive charge is either located on one of the nitrogen atoms of tetrazole ring or delocalized within benzene ring. Contribution of carbocationic type resonant form is rather small but it is not negligible. q 2004 Elsevier B.V. All rights reserved