Lastly, regarding the influence of meso-substitution there was only a marginal difference in the absorption spectra of the AL(DIPY)3 complexes and thus different substituents do not greatly affecting the absorption profile. This is in accordance with reports of similar compounds. DFT and TD-DFT calculations were conducted for representative complexes (13a, 13d, 13h, 13i, 17) by using a hybrid B3LYP functional and a LANL2DZ basis set. The aim was to visualize the frontier molecular orbitals (FMOs) and the electron-density distribution within the complexes. Additionally, the theoretical singlet S1 ( 1 E00) and triplet T1 ( 3 E00) excited levels of the AL(DIPY)3 complexes were determined along with the singlet-triplet gap (ΔES-T). As shown in Error! Reference source not found. there is no apparent electronic distribution in the metal center and indeed it was localized within the dipyrrin moieties confirming the inter-ligand excitation profile and the charge transfer between the ligands. This result is in accordance with the literature. DFT calculations of Ga(III) and In(III) analogues attributed the electronic distribution mainly as ligand centered in the intra-ligand charge transfer. Kusaka et al. investigated the heteroleptic tris(dipyrrinato)indium(III) coordinated complexes and showed that there is no significant influence of the metal center in the FMOs; the HOMO and LUMO are localized on the dipyrrin ligands. Ultimately, the computed triplet excited energy was found between 1.60-1.75 eV following the trend: 13d < 17 < 13i < 13h < 13a, which satisfies the prerequisite for a PS to generate singlet oxygen (T1 > 0.98 eV, the lowest excited singlet state of oxygen).