In acidic aqueous medium and in methanol, the formation of a 1:1 complex between Al(III) and protocatechuic acid (PCAH) was highlighted by electronic absorption spectroscopy. The ground and low-lying excited electronic states of the possible structures of the 1:1 complex were studied using DFT approach. Molecular and electronic properties were calculated using the VSXC functional, while excited singlet states were examined using TD-DFT methodology. A very good agreement in wavelengths was found between the theoretical electronic spectrum of a chelate involving the catechol group and the 1:1 complex experimental spectrum. (c) 2006 Elsevier B.V. All rights reserved.