In this work, the geometry, electronic properties and absorption spectra of low band gap organic dyes based on 2-styryl-5-phenylazo-pyrrole, C1, C2 and S dyes were theoretically investigated via DFT and TD-DFT in the gas phase and in solution. Theoretical calculations have been also carried out on the adsorption of these dyes on the TiO2 anatase (101) surface that show bidentate bridging is preferred adsorption mode in these dyes. Highest charge populated in the acceptor group, longest lifetime of the first excited state, highest electronic coupling constant (vertical bar V-RP vertical bar) of the S dye and the most negative shift of the conduction band of TiO2 due to the adsorption of the S dye on TiO2 (Delta E-CB) show that these parameters are favorable to increase V-oc. The calculated results of these dyes demonstrate that theoretical calculations are useful not only in the description of these properties, but also in the design of new sensitizers. (C) 2014 Elsevier B. V. All rights reserved.