Substituent effects on the fragments, intermediates and indigo dyes have been evaluated using global and local descriptors of the chemical reactivity. In terms of the global electrophilicity, one of the fragments, indoleninone, is classified as the electrophile and the other, indoxyl, as the nucleophile. The resonance, field and polarizability contributions of the substituents play an important role in the description of the fragments' electrophilicity. The interaction of the two fragments, to form the intermediate complex, has been shown to be as a superposition of two molecular planes, one coming from the indoxyl HOMO and the other from the indoleninone LUMO, both oriented by the dipole moment. Also, it has been shown that the complex formation is guided by the most nucleophilic indoxyl compound and not by the most electrophilic indoleninone. In spite of the indigoids having symmetrical structures, the substituent effects described in terms of the resonance, field and polarizability effects have an important effect on the maximum wavelength absorption in the electronic spectra.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry