Solvatochromic dyes that exhibit a negative or a positive behaviour may be distinguished and their solvatochromism predicted with the aid of DFT-based indices, such as their electrophilicity omega, hardness eta and by the Fukui electrophilic functions f(G)(+) of the donor and acceptor moieties of the molecule, calculated in the gas-phase and in solvents treated as polarised continua. The protocol was successfully applied to 10 examples of phenolate betaines from the literature, five of them exhibiting a negative and five a positive solvatochromism. (C) 2011 Elsevier B.V. All rights reserved.