Effect of Nitrogen Cation as "Electron Trap" at π-Linker on Properties for p -Type Photosensitizers: DFT Study.

On the basis of thieno(3,2-)thiophene and dithieno[3,2-:2',3'-]thiophene ( and moieties) as π-linker, the , and series dyes were designed to investigate the effect of the introducing N as an "electron trap" into and on the properties of the dyes. The optimized structures, electronic and optical properties were investigated by the density functional theory (DFT) and time-dependent DFT (TD-DFT). The results show that the properties of the dyes are sensitive to the N position in π-linkers. series dyes with electron-withdrawing units located near the donor have better properties than the corresponding series with the electron-withdrawing units located near the acceptor. For and series, the N modified dye named displays the largest red shift of the UV-vis absorption, the maximum integral values of the adsorption-wavelength curves over the visible light, the highest light harvesting efficiency (LHE, 0.996), and the strongest adsorption energy (-44.33 kcal/mol). also has a large driving force of hole injection (Δ, -0.74 eV), which results in a more efficient hole injection. Bearing a lengthier π-linker than , the properties of are further improved. moiety or its increased conjugated derivatives may be a promising π-linker.