AM1 and PM3 semiempirical calculations on 1-aryl-3,3-diethyltriazenes: correlation of bond orders with rotational barriers and quantum yields of photolysis

Abstract

Molecular geometries, electronic transitions, bond orders, and dipole moments are calculated for 19 l-aryl3,3-diethyltriazenes and two 3-alkyl- 1 ,5-diarylpentazadienes, using standard AM1 and PM3 semiempirical methods. Calculated UV spectra compare well with the experimental results, A strong correlation is established between the barrier to internal rotation, AG*, and the N2-N3 bond order. The photochemical decomposition of substituted triazenes and pentazadienes is of interest in view of their application as promoters in laser-induced polymer ablation. Therefore, the photolysis quantum yields at 308 nm are investigated in various solvents. The influence of substituents on the aryl moiety on the quantum yield is analyzed in terms of a correlation with the calculated N1=N2 bond order. The effects of different nitrogen-bound alkyl substituents on the photochemical decomposition behavior can be represented by a similar correlation. Differences between the photolysis behavior of triazene and pentazadiene derivatives are discussed.