The geometrical structures, electronic structures, spectroscopic properties of four red-emitting [PtR] [R=syn-dibenzoporphyrins (DBPs,1), 5,15-Diaryl-syn-dibenzoporphyrins (PDBPs,2), syn-dinaphthoporphyrins (DNPs,3), 5,15-Diaryl-syn-dinaphthoporphyrins(PDNPs,4) complexes were investigated by DFT and TDDFT methods. We first optimized geometrical structures in ground state(S₀) of four complexes, using three functionals (B3LYP, M062X, and B3PW91), and the excited state(T₁) structures was optimized by selected UB3LYP functionals. The calculation results were compared with relevant experimental data to assess the performance of the functionals. The calculated bond lengths of Ir-N and absorptions in the ground state agree well with the corresponding experimental results. At the TD-DFT and PCM levels, 1-4 give rise to lowest energy absorptions at 498, 507, 537, 545 nm and phosphorescent emissions at 684, 683, 761, 823 nm, respectively. The HOMOs of 1-4 are mainly localized on the porphyrins ligands, while the LUMOs are the π*(R) type orbital. Therefore, the transitions of 1-4 are all attributed to [π(R)→π*(R)] charge transfer. It is shown that the emitting color are significantly dominated by the porphyrins ligand itself , but are minor impact by the 5,15-substituent group.