Quantification of the push–pull character of the isophorone chromophore as a measure of molecular hyperpolarizability for NLO applications

The push–pull character of a series of para-phenyl substituted isophorone chromophores has been quantified by the 13C chemical shift difference of the three conjugated partial CC double bonds and the quotient of the occupations of both the bonding and anti-bonding orbitals of these CC double bonds as well. The correlations of the two push–pull quantifying parameters, and to the corresponding bond lengths, strongly recommend π CC ∗ /πCC as the general parameter to estimate charge alternation and as a very useful indication of the molecular hyperpolarizabilities for NLO application of the compounds studied.