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Color and Constitution of Azo Compounds
Author(s) -
Bock H.,
Rudolph G.,
Baltin E.,
Kroner J.
Publication year - 1965
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.196504571
Subject(s) - chromophore , substituent , chemistry , absorption (acoustics) , ultraviolet , photochemistry , phosphorus , computational chemistry , organic chemistry , materials science , optics , physics , optoelectronics
Attempts to explain the surprising violet color of the new azobisphosphonic acid derivatives Y 2 OPNNPOY 2 have led to the preparation and spectroscopic characterization of more than 60 azo compounds. The long‐wavelength n → π * transitions on which the color depends exhibit regularities which justify the assumption of substitutent‐specific absorption increments. The complex relation between color and constitution of azo compounds can be qualitatively explained with the aid of orbital models. Infrared and ultraviolet spectral data show that conjugation is inhibited by tetra‐coordinated phosphorus (V). the π‐system of these compounds therfore comprises only for atoms, P·N·N·P. The unexpected violet color of the phosphorus azo compounds can be ascribed to a π*/d orbital interaction. The substituent effects described have general significance, and n→π*transitions of other chromophores are similarly affected.