The structural and electronic properties of an organic dye C258 adsorbed onto the TiO2(101)surface with two adsorption modes,monodentate(Mha)and bidentate bridging(BBH),have been investigated by using the self-consistent-charge density functional tight binding method.A detailed analysis of the adsorbate contributions of the dye molecule with band states of TiO2 shows strong coupling of adsorbate orbitals with the substrate orbitals.Significant electronic transfer across the interface reveals a direct electron injection mechanism arising from the electronic excitation from anchor group of C258 to the conduction bands of TiO2.The electron density distributions of related frontier orbitals and adsorption energy of the two adsorptions systems demonstrates that BBH structure has a stronger coupling and a more stable geometry than Mha structure,which can better promote the electron injection.