Quantification of the push-pull character of donor-acceptor triazenes

The push-pull character of two series of donor-acceptor triazenes has been quantified by (13)C and (15)N chemical shift differences of the partial N(1)=N(2) and N(3)=C(4) double bonds in the central linking C=N-N=N-C unit and by the quotient of the occupations of both the bonding pi and antibonding orbitals pi* of these partial double bonds. Excellent correlations of the two estimates, to quantify the push-pull effect, with the bond lengths strongly recommend the occupation quotients pi*/pi, the (15)N chemical shift differences DeltadeltaN(1),N(2)], and the corresponding bond lengths as reasonable sensors for quantifying charge alternation along the C=N-N=N-C linking unit, for the donor-acceptor quality of the triazenes 1 and 2 and for the molecular hyperpolarizability beta0 of these compounds. Within this context, certain substances can be strongly recommended for NLO application.