Computational and experimental studies of the electronic excitation spectra of EDTA and DTPA substituted tetraphenylporphyrins and their Lu complexes.

Ethylendiaminetetraacetic acid (EDTA) substituted and diethylenetriaminopentaacetic acid (DTPA) substituted aminated free-base tetraphenylporphyrins (H2ATPP) and the corresponding lutetium(III) complexes have been studied computationally at the density functional theory (DFT) and second-order algebraic diagrammatic construction (ADC(2)) levels using triple-ξ basis sets augmented with polarization functions. The molecular structures were optimized using Becke's three-parameter hybrid functional (B3LYP). The electronic excitation spectra in the range of 400-700 nm were calculated using the ADC(2) and the linear-response time-dependent DFT methods. The calculated spectra are compared to those measured in ethanol solution. The calculated excitation energies agree well with those deduced from the experimental spectra. The excitation energies for the Qx band calculated at the B3LYP and ADC(2) level are 0.20-0.25 eV larger than the experimental values. The excitation energies for the Qy band calculated at the B3LYP level are 0.10-0.20 eV smaller than the ADC(2) ones and are thus in good agreement with experiment. The calculated excitation energies corresponding to the Bx and By bands are 0.10-0.30 eV larger than the experimental values. The excitation energies of the Bx and By bands calculated at the B3LYP level are in somewhat better agreement with experiment than the ADC(2) ones. The calculated and measured band strengths largely agree.