The structure of six recently synthesised neutral or charged 1-pyridylazulenes and 1,3-dipyridylazulene have been investigated with the PCM-PBE0/6-311++G(2d,2p) approach. Our calculations demonstrate that several conformers of similar energies might coexist in the experimental conditions. The absorption spectra of all derivatives have also been simulated with TD-DFT, and a very good agreement between the experimental and theoretical shifts is attained for both acidochromic and auxochromic phenomena. The origin of colour changes upon pH modi. cation is rationalized. (C) 2008 Elsevier B.V. All rights reserved.