The UV/visible spectra of a series of diazonium. (N-2(+)) fast dyes have been evaluated by using a time-dependent density functional theory approach explicitly taking into account bulk solvation effects. Using the PBEO functional with the 6-311 G(2d,2p) atomic basis set, the agreement between theory and experiment is excellent for these cationic species. The effects on the spectra of chemical substitution are analysed. (c) 2005 Elsevier B.V. All rights reserved.