Geometry, Electronic Structure, and Related Properties of Dye Sensitizer:3,4-bis1-(carboxymethyl)-3-indolyl-1H-pyrrole-2,5-dione

The geometry, electronic structure, polarizability and hyperpolarizability of dye sensitizer3,4-bis1-(carboxymethyl)-3-indolyl-1H-pyrrole-2,5-dione (BIMCOOH) were studied usingdensity functional theory (DFT) with hybrid functional B3LYP, and the electronic absorp-tion spectra were investigated using semi-empirical quantum chemical method ZINDO-l and time-dependent DFT (TDDFT). The results of natural bond orbital suggest that the natural charges of the dione, indole, and acetic groups are about -0.15e, -0.29e, and 0.44e,respectively. The calculated isotropic polarizability, polarizability anisotropy invariant and hyperpolarizability are 305.4, 188.3, and 1155.4 a.u., respectively. The electronic absorption spectral features in visible and near-UV region were assigned to the ∏→∏*transition due to the qualitative agreement between the experiment and the TDDFT calculations, and the transitions of the excited states 9-11 related to photoinduced intramolecular charge transfer processes. The analysis of electronic structure and UV-Vis absorption indicates that the indole groups primarily contributed sensitization of photo-to-currency conversion processes, and the interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer BIMCOOH are electron injection processes from excited states of the dyes to the semiconductor conduction band.