Spectroscopic and electrochemical properties of para-methoxyazobenzene derivatives

Abstract

Ultraviolet photoelectron spectroscopy, gas-phase absorption spectroscopy, polarographic half-wave reduction potentials and INDO/S-CI molecular-orbital calculations have been employed to investigate the electronic structure of some p-methoxyazobenzene derivatives. The photoelectron bands in the low-energy region of the spectrum have been assigned. The ag(n–) and the au(π1) ionizations display almost the same sensibility towards the substituent. The observed trends are qualitatively predicted by calculation. The electronic transitions are interpreted with the aid of INDO/S-CI calculations. Use is also made of the approach of Haselbach and Schmelzer approach. Reversible half-wave reduction potentials are used as a measure of the solution electron affinity of the molecule. Good linear relations are found between E1/2 and ELUMO and the Hammett σ constant. Correlations between electrochemical and spectroscopic data provide evidence that variations in the experimental transition energies along the series, with the exception of the nitro-derivatives, originate from changes in the (–J+ 2K) and ΔGsolv terms.