Spektralverhalten von Pyrazolin‐5‐on‐Azomethinfarbstoffen – Quantenchemische Beschreibung der Substituenteneinflüsse

Absorption Behaviour of Pyrazoline-5-one Azomethine Dyes – Quantumchemical Description of the Influence of Substituents The VIS absorption of the pyrazoline-5-one azomethine dyes 1a–h is measured in dependence of the substituents of the amino group. HMO calculations confirm that the „x- and y-bands” have a strong charge transfer character. The absorptions in the visible region correspond to a transition from the HOMO mainly localized at the amino-substituted phenyl to the complex acceptor 4-imino-pyrazoline-5-one (“x-band”) or to the pyrazoline-5-one fragment (“y-band”). The calculated transition energies correlate with the values νmax of the x-band (r = 0.993). There is also a linear correlation between the square of the LCAO-MO coefficients in position 7 and 6 of the dye and emax (r = 0.978).